Monday, December 31, 2007


The following observations taken here at the house - north end of Country Club about a half mile south of the Rillito Wash - document what was an unusual early December rainy period that was followed by a very cold last half of December. Note that the part of Tucson we live in is considerably lower in elevation than the official NWS observation site at the airport on the far south side of the city. On clear and calm nights low temperatures here at the house are routinely at least 8 to 10 degrees F colder than the "official" readings at the airport. I do not record maximum temperatures here at the house because I have never been able to screen my max/min thermometer adequately to avoid contamination by daytime solar heating.

December 2007 Precipitation (I read my gauge at about 7 am each morning so that some rainfall may have actually occurred after midnight and technically be for the next day):

Dec. 1 - 1.84" No thunderstorms observed at house
Dec. 2 - 0.05"
Dec 7 & 8 - 0.62" We were out of town from Friday afternoon until Sat. evening.
Dec. 9 - 0.04"
Dec. 10 - 0.23" Strong thunderstorms occurred late afternoon on Monday and pea size hail fell here at the house at dusk.
Dec. 11 - 0.40"
Dec. 12 - very dense fog until about 11 am in the morning.
Dec. 21 - 0.05" In addition to the light rain there was a brief burst of snow pellets here at the house about 9:30 am. Weather broadcasts erroneously referred to the occurrence of sleet around town.

Total December precipitation: 3.23 inches

Minimum temperatures:

24 days had lows of 39F or colder
16 days had lows of 29F or colder
3 days had lows of 19F or colder

An extended period of very cold morning lows (at least for here in Tucson) began the morning of the 15th - as per:

15th - 24F The first hard freeze with very heavy frost here at house.
16th - 24F
17th - 29F
18th - 29F
19th - 29F
20th - 27F
21st - 36F
22nd - 21F
23rd - 19F
24th - 24F
25th - 26F
26th - 18F
27th - 23F
28th - 19F
29th - 22F
30th - 24F
31st - 24F

The extended period of cold temperatures caused fairly heavy plant damage here at house, and I hauled out about 100 lbs of broken and fallen cacti arms this morning.

My summary of the entire year, highlighting significant weather events, will follow by the end of the week.

Happy New Years to all!

Friday, September 07, 2007

Henriette and Today's Weather

Rain from Henriette

Here at the house we received only 0.03" of rain on the afternoon of the 5th (Wednesday) but very heavy storms occurred in the vicinity (see Photo). We experienced considerable lightning and thunder and gusty outflow winds but little rain. Then, during the early morning hours of Thursday from about 5 am to 9 am there were several moderate showers with no lightning or thunder here. These produced an additional 0.41" of rainfall. Henriette has left behind a very wet low-level atmosphere and the forecast for today is of interest.

Today's weather

There is a large pool of very moist air lingering over much of Arizona this morning, along with considerable low and middle level cloudiness.

Winds in the lower half of the troposphere remain L/V while upper-level winds and shear are quite strong (this due to strong height gradients between the anticyclone to the southeast and a trough off the Pacific coast). The upper-levels appear to be divergent over southeastern Arizona.

The morning TWC sounding indicates substantial CAPE is present below 350 mb. The questions for the day are: how believable is the TWC sounding, and how will drying during the day affect the CAPE? In the morning soundings in the layer between 400 and 300 mb there is a pronounced inversion between the moist lower atmosphere and the dry upper-levels. At TWC the inversion is about 7C warmer than at any other upper-air site in the Southwest. To me, the TWC sounding appears suspect between 520 to 280 mb. My guess is that the elevated inversion is not as strong as indicated here, and that it will not strengthen due to the dry flow aloft, so that there is at least moderate CAPE present.

I expect that strong storms are likely this afternoon over the southeastern third of Arizona, especially where the clouds break and there is decent solar heating. The storms should have the potential to produce strong, moist downbursts and some hail, especially at higher elevations.

All this assumes that I have been able to properly unravel the uncertainties in the upper-air data.

Wednesday, September 05, 2007

Forecast Remains Difficult

See yesterday's message about tough forecasts!

Today we have moisture and hopefully CAPE will remain through the day -we are getting some mid-level warming now. Upper-level winds are difluent between the hurricane and the system to NW. Winds are very light in lowest half of troposphere - again. Low-level winds become southwesterly during the day and there is more IPW to the west. So, there should be storms around this afternoon with the potential for heavy rains.

Tomorrow is much tougher and it's possible that it will be an all or nothing situation here in the Tucson area. Who remembers Nora?

NAM forecasts a decent rainfall event, but keeps the really heavy rain with the core of what was Henriette. It is of note that there were soundings this morning at La Paz and Guaymas for the first time in ages, so the model actually had some observations in its initialization.

Negatives tomorrow are that NAM forecasts winds to become strong downslope below 500 mb into the local area. This is coupled with what appears to be fairly strong confluence aloft. The GFS members forecastsignificant rain event also but, of course, local terrain really isn't in that model.

If the remains of Henriette move northward to the west of the NHC and NAM tracks, get out the sandbags!

So, I conclude that, with so many uncertainties in the next 24 hours, the only thing to do is to watch the observations closely and see what actually transpires during the afternoon and night.

Tuesday, September 04, 2007

Henriette Leads to Rapidly Changing Conditions over Southern Arizona

A Very Difficult Forecast Situation

The last two days have been extremely suppressed and very dry in southern Arizona, with dewpoints yesterday falling into the upper 30s. This was the third dry-down of the summer that came in on easterly to southeasterly winds.

This morning a number of things have changed. There has been a northward surge of low-level moisture into southwest and south-central Arizona during the late night and early morning hours. This was likely triggered by strong winds to the northeast of Hurricane Henriette. At 7 am the moisture had increased dramatically at Yuma, Sells, and Sasabe. The VAD Doppler radar data at Yuma indicate that this surge is about 3,000 ft deep. It may provide enough destabilization for at least mountain storms over the southern third of the state this afternoon.

The track of Henriette will then be the key determining factor for the weather over southeastern Arizona. The models now are in fair agreement that Henriette should move into the southern GoC. Tomorrow there will be a strong isallobaric wind blowing down the GoC and that may slosh today's low-level moisture back toward the south. Then, the main issue becomes how far north the deep moisture and precipitation fields associated with the weakening storm will come.

It appears that the current trough in the northwest will move rapidly over the top of the middle-level anticyclone leaving some remnants of Henriette blocked and decaying over northern Sonora and the GoC. This would allow the moisture associated with the storm to move directly into at least southeastern Arizona and give the potential for a significant rain event.

Monday, September 03, 2007

Yuma Storm on Saturday

I have checked the Yuma newspaper this morning and there are two stories online that describe the intensity of the severe thunderstorm that struck Yuma Saturday evening. There are numerous damage photos available - and perhaps even a video (I couldn't get it to play though).

Sunday, September 02, 2007

A Big Storm Day in Southern Arizona and California

Yesterday afternoon , Saturday September 1st, turned out to be a big storm and severe storm day across southern Arizona and into southern California. There were several small tornadoes in California, and events in Arizona were mostly from hybrid downbursts, although there was one hail report. Most notable was a measured gust to 84 mph out at Yuma, Arizona. I have not yet chased down many photos, but will try to post some damage shots tomorrow.

Strong, drying easterly winds today have led to mostly suppressed conditions across southern Arizona, with significant storm activity focused in southern California.

Data from TWC yesterday provide a good illustration of how difficult it is to use RRS soundings with suspect data in making a forecast.

In my previous post I noted that the 12 UTC (1 Sept. 2007) sounding at TWC was suspect and that it was difficult to estimate what the CAPE might actually be in the afternoon. I guessed that a well-mixed afternoon BL might have a mixing ratio of ~9 g/kg. But I also mentioned that 1 g/kg either way would have substantial implications for the evolution of afternoon storms. The TWC sounding at 00 UTC (2 Sept. 2007) apparently entered a storm updraft - see Figure 1. The data are mostly bad or suspect, except for the temperature trace from the surface to about 650 mb. However, the updraft data from 500 to a bit above 400 mb have theta w values of 24 to 25C. This implies that the BL air at cloud base had a mixing ratio of 10.5 to 11.5 g/kg.

My morning estimate, using the sounding with the suspect Td trace, was clearly way too low. It is fairly obvious that moisture advection, given the winds below 650 mb for the morning and evening soundings, was not a major player during the day. Figure 2 shows the morning sounding with lines added showing q = 10 g/kg and theta w = 23.5C. The Sippican hygrister appears not to have responded well at all in the residual layer and indicated conditions that were too dry.

It is likely that the sounding problems yesterday contributed to forecasts that significantly under-estimated the extent of the severe storm outbreak. And so it goes in the new era of NWS RRS soundings - a serious crap shoot for forecasters that sometimes has public safety implications.

Saturday, September 01, 2007

Weather Discussion 1 Sept. 2007

There have been many interesting changes from yesterday morning to this morning.

Atmosphere has moistened up some wrt IPW, but the soundings are very hard to interpret.

Last evening's TWC sounding (see Fig. 1) had a dry spike off the surface and then seemed to indicate a BL with a bit less than 8 g/kg and IPW of 25.8 mm (this was extremely dry wrt the GPS value). The evening sounding appeared to have no CAPE - but storms developed to the south of the airport around 0200Z and TUS carried a brief tstm (nice lightning visible from here with this cell).

This morning's sounding (see Fig. 2) has IPW of 37.5 mm, quite a large increase of almost 12 mm in 12 hours according to the soundings, but GPS data (see Fig. 3 from FSL) show a 12 hour increase of only about 2.5 mm. So, once again, the first forecasting dilemma for today is that of trying to figure out what the local thermodynamic conditions actually are.

The morning sounding has NO residual BL in moisture but a very deep residual BL in temperature. I'm going to guess that it's there (a residual BL in moisture) and that the mixing ratio we're heading toward is about 9 g/km. This would give a decent amount of CAPE this afternoon. But if I'm off by either +/- ~1 g/kg, the difference goes from a marginal day with mostly mountain storms to a very good day at low elevations with moderate CAPE available for storms. The deep BL and high cloud bases leads to either the potential for dry microbursts, or to severe hybrid downbursts at lower elevations - all depending upon what the afternoon BL actually looks like.

Am I frustrated trying to use bad sounding data to make a forecast? VERY!

Other interesting aspects of today's forecast:

Surface pressures are down 2 to 3 mb in south-central AZ compared to 24 hours ago.

An upper-level S/W trough is swinging southward across New Mexico, giving much of AZ flow aloft that is quite difluent.

Easterly low-level winds are still present but have diminished quite a bit. It will be important for the evolution of storms this afternoon if WNW diurnal winds can develop - the lower deserts to west and northwest are more moist than the local area.

Steering level winds are around 10 to 15 kt from the north, but anvil level winds are also northerly at about 20 kts. Thus, unless storms can propagate rapidly southward, anvil cloud will spread out ahead of the cells - not favorable for storms at lower elevations.

Thus, it's a very difficult call for lower elevations. Mountain and higher elevation areas should be very active. Will significant storms occur at lower elevations of southeast AZ? It's probably a coin toss, and we'll just have to see what kind of event unfolds this afternoon and evening.

As for TS/possible Hurricane Henriette, the NAM and the GFS have much different scenarios predicted for the storm. The NAM takes the storm fairly quickly into the area around the tip of Baja. This would not trigger a surge of low-level moisture into Arizona until the storm remnants actually moved to the north end of GoC or northern Sonora. The GFS takes the storm northward considerably further to the west, along a track that would trigger a significant surge. The GFS then brings the storm remnants right into southern AZ for a big rain event. However, it appears that only the operational GFS has this solution, and all the other GFS ensemble member forecasts from 0600 UTC hardly indicated that Henrietta exists. So, there are more coin tosses in the long-term outlook also.

August Weather Summary

A quick summary of what August brought here at the house.

Rainfall - 2.21" (less than half of July's 4.94")

Measurable precip - 8 of 31 days

Trace or more - 13 of 31 days

Thunderstorms in general area - 19 of 31 days

Severe thunderstorms in Tucson area occurred on: 10th, 14th, and 24th

Heavy tstm rains on the 4th produced severe flash flooding and several fatalities in Sabino Canyon.

All in all an active month, but much less so than was July.

The WRF run yesterday indicated that we might see a considerable increase in storm activity today. So, I'm about to see what the morning observations and products are saying. I will note that at sunrise today there were patches ofmiddle cloud floating around in all quadrants with some ACC present toward the south. This is much different than yesterday's sunrise, when there were only some wispy cirrus and lenticular clouds.

Thursday, August 30, 2007

Last Weekend's Storms Near San Diego

I have been away from the weather for most of the past week, as I had to prepare a book catalogue for mailing before the Labor Day weekend. I now have a bit of time to catch up on weather events and the like.

Jim Means, who is an avid storm watcher and monsoon follower, sent information at the first of the week, as per:

"Finally a big monsoon today over here in Southern California. The combination of an upper level disturbance offshore from San Diego and a deep moisture field (PW ~ 2") from the remnants of Hurricane Dean gave San Diego County its best monsoon day in quite a while. Lifting caused by the upper level disturbance initiated storms before sunrise, and the NWS in San Diego had to issue an unusual Flash Flood Warning for the area around Escondido, about 25 miles north of San Diego. A strong (but not severe) storm produced flash flooding and some areas got more than 2 inches of rain in about an hour and a half. Another storm occurring at the same time produced a waterspout offshore from San Clemente. Daytime heating later generated another flash flood producing storm in the area of Anza Borrego Desert State Park, where people had to be rescued from their cars in what are normally dry washes. This storm generated 3 inches of rain in some places and the NWS reported the top at 60,000 feet."

Jim, who lives in Alpine CA - which is east of San Diego along I-10, has sent a couple of photos of interest:

Photo 1, taken by Jim at sunrise on Sunday 26 August, shows the early morning storm near Escondido, north of Alpine.

Photo 2 shows Escondido Creek still running in flood on Monday morning.

Friday, August 24, 2007

More Information on Missing Winds in the NWS Upper-Air Soundings

I took a quick look at the soundings from yesterday evening and from this morning. At least the following soundings have missing wind data:

0000 UTC 24 August 2007

RAP sfc - 620 mb
LCH sfc - 400 mb
SHV sfc - 600 mb
TLH sfc - 720 mb
MHX sfc - 680 mb

1200 UTC 24 August 2007

BOI sfc - 600 mb
TFX sfc - 700 mb
MAF sfc wind is only wind for entire sounding
TLH sfc - 680 mb
MHX sfc - 780 mb
IAD sfc - 750 mb
BUF sfc - 780 mb

I browsed though the soundings at the Storm Prediction Center (SPC) site:

These soundings now display only the actually observed winds aloft.

I would imagine that such serious losses of wind data would be having negative impacts on the models and also upon forecast operations at places such as the SPC.

Discussion of the TWC Sounding for 0000 UTC 24 August 2007

The TWC sounding taken yesterday afternoon Figure 1 illustrates several of the serious problems with data from the NWS RRS Sippican sondes. I discuss the sounding layer by layer beginning at the surface:

* Abrupt jump in Td at release - reason for this is unknown. See my earlier post on the Madweather webpage regarding the roof-top launch conditions at TWC.

* The afternoon boundary layer (BL) in T extends upward to 700 mb; however, the Td trace from 900 to 780 mb does not depict a well-mixed BL in moisture. My guess is that this reflects a slow response of the hygrister back toward actual values, after the abrupt Td excursion at release.

* A realistic portion of the BL is is sampled from 780 to 700 mb.

* The sonde apparently entered a towering cumulus at about 660 mb and experienced severe wetting of the thermistor and perhaps of the hygrister. The data are extremely bad from 600 to 400 mb affected by evaporation, and perhaps freezing, and sublimation. Note - I was inthe immediate vicinity of the launch site and there were no thunderstorms present; however, a deep and thick mesoscale anvil covered the sky from the WSW through the ENE. The equally absurd ASOS surface observation from TUS at this time was "CLR."

* From 400 to 300 mb the sensors are apparently slowly recovering toward values present in the actual atmosphere.

* Above 300 mb the data remain suspect; are extremely smooth; and do not reflect the presence of the ice saturated anvil cloud.

* The temperature data from at least 600 to 300 mb appear too cool. Since the thermodynamic data are used to compute the heights of the pressure surfaces, it is not surprising that heights at and above 300 mb appear 20 to 40 m too low.

Thus, it is likely that this sounding had physically realistic data for a single layer that was only about 80 mb deep!

I certainly hope that these data do not end up in the NCDC sounding data archive.

Thursday, August 23, 2007

Winds Aloft Problem with RRS sondes - Today's Worst Example

While I didn't have time to plow through the details of all the NWS RRS Sippican soundings this morning, the worst example was not hard to find. The upper-air sounding at Boise, ID (WMO 72681), 1200 UTC, 23 August 2007, observed no winds above the surface.

I keep hoping that the NWS will formally alert external users of upper-air data, whether the users be proviate forecasters or the university and research community, of the problems that are plaguing their new RRS soundings.

As far as I know, such information has not been shared with the external user community - if my assessment is wrong, please let me know. Thanks. Bob

Sunday, August 19, 2007

Overview of Problems with Data from the RRS Sippican Sondes

I have seen a copy of an internal NWS issue paper on the RRS sonde, including "talking points" for the media. After reading this document, I have a number of concerns:

The sonde problem is apparently being approached by higher levels of the NWS as if it is essentially a problem related to the performance of the Sippican hygrister in dry, desert environments.

In my opinion, nothing could be further from the truth.

After looking at many RRS soundings during the past month and a half, I conclude that there are serious problems with both the hygrister and the thermistor and, probably, with the sonde's internal electronic components. This last statement is just a hypothesis, since I don't know much about the technical details.

I am collecting bad RRS soundings from all over the country so that I can provide an extensive documentation of the problems. I provide here a quick overview of theproblems I have seen to date:

1 - Extreme dry layers above the surface with a slow recovery, leading to soundings that are too dry. (Note that this "too dry in low levels" problem was first detected by NWS personnel in the Southwest. However, the NWS instruction manual for operators of the RRS system indicates that other of the sonde's problems were detected during evaluation; however, implementation proceeded regardless.) See Fig. 1.

2 - Slow response to dry layers aloft when sonde is launched in a relatively humid environment, leading to occasional soundings that are too wet. See Fig. 2 and post of August 8th.

3 - Both the thermistor and hygrister are apparently poorly vented and one or both are easily wetted, leading to a plethora of problems caused by the latent heat effects of condensation, evaporation, freezing, and sublimation. (The wetting problems apparently relate to the compact size of the new overall instrument package that was evidently developed initially for military field use.) See Fig. 3 and Fig. 4.

4 - The RRS soundings are sometimes missing winds through significant layers (the ultimate example of which I distributed the other day - for a MN sounding, hardly a desert environment!) - See a previous post made today. The problems the missing winds can cause are many, some of which have serious implications for forecasting. This problem may be related to the sonde's internal electronic components. See both Fig. 1 and Fig. 5.

5 - Other problems, again probably related to internal electronics, cause high to veryhigh frequency noise leading sometimes to many many "special" points - in bothT and Td. See Fig. 6.

Avoiding GEMPAK Interpolation when Processing Upper-Air Soundings

The following information on how to avoid interpolation within the GEMPAK code has been provided by David O. Blanchard - many thanks!

The fix for the interpolation of winds and temperatures in GEMPAK is not difficult.

GEMPAK can store upper-air data in two formats: merged and unmerged.

Unmerged data sets will store the TTAA, TTBB, and PPBB data as separate parts. There is no interpolation of the data.

Merged data sets combine the TTAA, TTBB, and PPBB parts and contain values for each parameter (P, T, Td, Dir, Spd, and Z) at each level and interpolates the data.

To avoid interpolation, the data must be saved unmerged. This is specified with the "MRGDAT" variable in GEMPAK when originally creating the upper air file.

Most sounding programs that use GEMPAK upper-air data will call SN_RDAT to read the data; SN_RDAT calls SN_MERG to merge the TTAA/TTBB/PPBB data if they are not already merged; SN_MERG calls MR_UADT which calls MR_MISS to interpolate the data.

Only MR_UADT needs to be modified. Copy the MR_UADT source code and the required INCLUDE files to your sounding software directory. Edit MR_UADT and comment out the line that calls MR_MISS. Compile your sounding source code and the modified MR_UADT source code.

The necessary code is found in the following locations:

./gempak/include/MCHPRM.PRM (rename MCHPRM.machineType to MCHPRM.PRM)

This patch prevents interpolation of the upper-air data in your sounding program but makes no changes to GEMPAK and its programs and libraries. Your sounding program must handle the uninterpolated data arrays
(i.e., it must be able to handle missing data flags of -9999.)

Example of merged TTAA/TTBB/PPBB data with interpolation:
603.0 3.8 -45.2 298.7 4.4 4375.2
589.0 2.8 -46.2 295.5 4.7 4565.5
558.0 -1.1 -36.1 288.1 5.4 4999.7
546.0 -0.3 -49.3 285.2 5.6 5173.3
545.4 -0.4 -49.4 285.0 5.7 5182.0
505.0 -5.1 -54.1 280.6 5.2 5791.9
500.0 -5.5 -53.5 280.0 5.2 5870.0
485.7 -6.2 -54.2 260.0 4.1 6096.0
477.0 -6.7 -54.7 261.5 4.6 6237.0
431.2 -12.6 -58.4 270.0 7.2 7010.0
416.0 -14.7 -59.7 252.0 6.3 7284.9
414.3 -14.8 -59.4 250.0 6.2 7315.0
400.0 -15.9 -56.9 255.0 7.7 7580.0

Example of merged data TTAA/TTBB/PPBB without interpolation:
603.0 3.8 -45.2 -9999.0 -9999.0 4375.2
589.0 2.8 -46.2 -9999.0 -9999.0 4565.5
558.0 -1.1 -36.1 -9999.0 -9999.0 4999.7
546.0 -0.3 -49.3 -9999.0 -9999.0 5173.3
545.4 -9999.0 -9999.0 285.0 5.7 5182.0
505.0 -5.1 -54.1 -9999.0 -9999.0 5791.9
500.0 -5.5 -53.5 280.0 5.2 5870.0
485.7 -9999.0 -9999 .0 260.0 4.1 6096.0
477.0 -6.7 -54.7 -9999.0 -9999.0 6237.0
431.2 -9999.0 -9999.0 270.0 7.2 7010.0
416.0 -14.7 -59.7 -9999.0 -9999.0 7284.9
414.3 -9999.0 -9999.0 250.0 6.2 7315.0
400.0 -15.9 -56.9 255.0 7.7 7580.0

Missing Winds from RRS Soundings - An Extreme Example

On Monday afternoon, August 13, 2007, Rob Dale and Eric Hanson alerted me to the strange characteristics of the special 1800 UTC sounding from MPX (Chanhassen, MN, an RRS/Sippican sonde site).

The unbelievably smooth hodograph is what had caught their attention. The sounding, as analyzed by software analysis programs at the Storm Prediction Center (SPC) is shown in Fig. 1. Note the perfectly smooth hodograph and the winds that back continuously from the surface to 150 mb. This seems a very strange sounding indeed!

However, examination of the sounding at the FSL RAOB site indicated what the problem was. The MPX sounding at FSL (Fig. 2) indicates that the Sippican sonde apparently lost GPS tracking immediately off the surface and did not recover the signals until 150 mb - i.e., the winds were actually missing from the surface to 150 mb.

So where did the "data" plotted at SPC come from? It turns out that many sounding analysis programs use, as part of their code, GEMPAK. The GEMPAK procedure interpolates data into layers where observations are missing - assuming probably that such layers are never very deep.

The sounding plot from the Univ. of Wyoming site (Fig. 3) shows interpolated winds that are similar to those on the SPC plot. However, Lance Bosart alerted me to look at the same sounding at the UCAR/RAP upper-air site (Fig. 4). Their plot shows a completely different wind profile through the troposphere! Apparently, RAP software uses a different interpolation procedure. The winds in their "answer" for the deep layer of missing observations essentially keep the direction at 150 mb constant, while decreasing the speed smoothly until near the surface, where a shallow layer of backing winds is shown.

While I'm not sure what impact this comedy of errors might have had on forecasts during the afternoon of August 13th, it does vividly illustrate how serious the Sippican missing winds problem can be. I have been alerted by a number of people around the country about the missing winds problem, and I will document it further at a later time. However, this is a particularly insidious problem for non-NWS users of the data. If one suspects that a sounding may have missing winds, then a time-consuming examination of the sounding at different sites has to be made for accurate evaluation.

Wednesday, August 15, 2007

Severe Storm Complexes Two Nights in a Row

I have chased down some photos of damage that occurred in Casa Grande on Monday night. See Photos 1-3.

As for yesterday afternoon (Tuesday Aug. 14) - I was out on east side when storms rolled through around 3:30 to 4 pm. Thought I saw several wall clouds, and there was a spectacular hail shaft out over Oro Valley around 4:30 pm. Of course my camera was back here at house! I see that there was wind damage reported in Oro Valley with the afternoon storm.

I note on the SPC page that there was severe hail NW of Flagstaff yesterdayafternoon and also a damaging microburst in Riverside CA!

I was very surprised by the early storm developments yesterday afternoon. Obviously, I did not properly adjust and then forecast the morning sounding - at least there's now another "out" available, given the bad Sippican sounding data!

MCSs developed again during the night (Tuesday night) and the activity continues this morning in south-central AZ. Tucson, Casa Grande, and Phoenix Skyharbor all reported gusts over 50 mph near or after midnight. Phoenix reported a severe gust to 59 mph,and there was wind damage near the Tucson airport.

The question for today is whether we'll experience similar intense and severe storms for the third afternoon/night in a row? The soundings this morning appear similar to yesterday (TWC again too wet wrt GPS IPW) with at least moderate CAPE available given decent heating, and the low-levels remain cooled by the recent outflows. The steering winds remain relatively strong and there is better directional shear aloft with another inverted trough approaching. I am again thinking that activity should be late and after dark, but the NAM seems to convect early and to move another organized line across southern AZ during the mid-afternoon. We will see, and I'll keep my camera at hand today.

The weekend could be interesting if part of the tropical system over Gulf of Mexico breaks off and comes across Sonora and southern AZ.

Sunday, August 12, 2007

Additional Commentaries on the Damage from Friday's Severe Thunderstorm

From Jim Toth:

Driving west on Orange Grove, I did not see anything significant until approaching the intersection at Oracle. The Park Place apartments are on the north side of OG, and that's where you start to see large trees down.

North on Oracle, the damage sticks out on both sides of the road all the way north to Ina. Aside from trees down and stripped green leaves obscuring parking lots, the most impressive thing I saw was the Long Realty building on the west side of Oracle. They had a large number of clay roof tiles peeled back and settled at odd angles.

At the Safeway parking lot at Oracle and Ina, there were a few large mesquite trunks snapped. These were out near Oracle. West on Ina, at the UMC medical offices, just east of Safeway, there were two large trees down near the entrance. Farther east on Ina, and then south on First, I did not see anything.

Steve Mullen reporting from Boulder:

My oldest son Ryan got caught in the teeth of the macroburst that nailed the NW side yesterday. He was driving along Ina between La Cholla and Oracle before heading southbound Oracle to Orange Grove around 6:10 to 6:15. Ryan reported two snapped stop signs, a leveled ~100-year saguaro, too many downed big trees to keep track. The sign in front of HiFalutin Restraurant was completely snapped. It was raining and blowing so hard near Ina and La Canada that he had to pull off the road.

Ryan shortly thereafter experienced some small hail. The Tucson Citizen had a blurb stating that winds were 60 mph over the NW side. I agree that they were 60 mph, for a moment, before gusting faster. It would take far more than 60 mph to down all that got leveled last evening.

Saturday, August 11, 2007

Forecasting SE AZ Convection using Unreliable Upper-Air Sounding Data from NWS/TWC

The last two soundings taken at TWC illustrate how frustrating it can be trying to use unreliable data from the new NWS Sippican sondes. The sounding from 00 UTC on 11 August is shown in Fig. 1, and the 12 UTC sounding on 11 August is shown in Fig.2.

The FSL time series comparing GPS IPW with TWC sounding IPW is shown in Fig. 3. The sounding last evening was too dry by 5 mm wrt GPS IPW and this morning's sounding is too wet by 5 mm wrt GPS IPW. The forecaster apparently didn't notice this problem this morning:


RE: Fig. 1

The afternoon sounding yesterday is particularly difficult to resolve meteorologically.
First, the surface super-adiabatic contact layer seems to extend upward to 900 mb. Possible I guess, but it also may be because a dry-spike data point was eliminated by the person who processed the sounding. I have no way to determine whether this was the case.

Second, where is the missing moisture located in the vertical? Since the well-mixed BL in theta extends up to 700 mb and the well-mixed q BL extends only to about 780 mb, I suspect that the "missing" moisture was likely in the upper-part of the BL. This sounding was taken in proximity, in both time and space, to a severe thunderstorm, I think that the CAPE was probably greater than the 314 indicated by the sounding analysis software. These sounding problems may have affected the timeliness of the severe thunderstorm warning that was issued at 6:22 pm.

Obviously, unless this sounding is somehow flagged as suspect in the data archives, a future researcher could consider it a valid severe thunderstorm proximity sounding, leading to………..

RE: Fig 2

This morning's sounding is also very difficult to analyze wrt to the likelihood of afternoon storms. Question is where is the "extra" moisture hiding in this sounding?
It is probably not in the spikey (noisy) data above 620 mb (some Sippican soundings are characterized by extremely noisy T and q data points for unknown reasons). The strange layer from 900 to about 840 mb is my guess for the layer that is too moist. I estimate that a BL well-mixed in q this afternoon would be one with q of ~ 11 to 12 g/kg.

While the mountains will have storms today, it is not clear how the lower elevation BL may evolve. It will likely have CIN above it's top, and if warming occurs in mid-levels, may end up not supportive for storms trying to move to lower elevations. But this is all guess work - since I don't know what the thermodynamic structure is below 700 mb to begin with, it is very difficult to try to predict what the afternoon structures are likely to be.

As for my forecast for our house - that's much more simple. Regardless of what happens to the south, unidirectional southerly flow is very unfavorable for storms and measurable rain at this particular spot. So, I would say that POPs here at our house are near zero today.

Storms in Tucson Metro Area on Friday 10 August 2007

Storms did develop over much of southeastern and south central Arizona yesterday. However, Cochise County in the far southeast was relatively suppressed, perhaps because dry air from New Mexico and northern Mexico invaded that part of the state.

Here at our house, we began hearing thunder from storms on the Catalina Mountains by 4:30 pm. I took Photo 1 of the initial developments over the Catalinas at 3:45 pm, looking NNE. My estimate is that cloud bases were at 700 mb or a bit lower, which fits with what one would expect from yesterday morning's TWC sounding.

The evening sounding was quite dry and this morning's (Saturday 11 August) is too moist. More on the problems of trying to forecast storms using the flawed data from the NWS/Sippican sonde in the next post.

I took Photo 2 at about 5:15 pm, again looking NNE. At this time frequent lightning was visible, along with lots of rumbling thunder. Updrafts had built southward from the mountains. There was another cell off to the ESE that had come off the Rincon Mountains, and new updrafts were forming between them. Photo 3 shows the Catalina storms in a view to the N, i.e., a bit to west of my Photo 2. The storms from the Rincons and the Catalinas apparently merged over the north side of town and then moved westward as a severe thunderstorm, producing damaging downburst winds.

Here at house we experienced strong wind gusts of 40 to 55 mph (estimated) from about 5:50 pm until about 6:20 pm. Winds were initially from the east with lots of dust, then from the northeast, and finally from the north (I think, since visibility was near zero in heavy rain at this time). Rain accumulation here was only 0.29". Jim Toth reported 0.97" a couple of miles to our NW.

Photo 4 shows the view of the storm from campus at 5:54 pm looking N. The ragged appendage, ahead of the outflow, showed some rotation as I observed it from the house. Note that the updraft and leading edge of rain shaft show green coloring, and small hail was indeed reported with the storm. Photo 5 shows some of the wind damage produced by the storms outflow, several miles to our NW.

All in all, quite an interesting afternoon here!

Friday, August 10, 2007

Interesting Storm Day Developing over Southern Arizona

Looks like a very interesting day setting up locally.

Very nice push of low-level moisture into most of southern Arizona after midnight, makes today quite different than yesterday thermodynamically.

The TWC morning sounding exhibits a low-level structure that's often associated with such nighttime moisture pushes, and I think that it is a reasonably good representation of morning conditions - one of the few times this week. The sounding, with the middle-level cooling and added moisture, indicates moderate CAPE lower elevations and even more unstable conditions higher elevations. The strong storms to our south and southeast last night crashed as they moved toward lower elevations. Today should be better, with storms coming into the lower elevations.

The morning NAM indicates a good setting by evening with upper-level difluence, and 15 to 20 kt steering winds at 500 mb. All of this due to an upper-level inverted trof brushing over the top of the malingering weak wave at lower levels. The dilemma of course is that the NAM has been forecasting stronger middle level winds than have been observed the past few days - so we have to wonder whether conditions will be as good this evening as NAM suggests.

The VAD winds this morning show L/V winds aloft - except for KYUX which shows that the surge extends up to at least 6000 ft agl. So, the evolution of the wind field today will likely determine how aggressively storms move into lower elevations. A good day to watch the Doppler winds and the Ft. Huachuca profiler winds closely.

My guess is that today will be quite active SE third of state with possibility of strong to severe hybrid downbursts and locally heavy rains. Storms here at house? Probably at least a 50% chance or better.

Wednesday, August 08, 2007

An Examination of Suspect Thermodynamic Structures in the Tucson Upper-Air Sounding AT 12 UTC 8 August 2007

Those who have read my previous posts are aware that I have been documenting data problems in upper-air soundings taken by the NWS using the new Sippican sonde. This morning's TWC sounding illustrates a suspect thermodynamic structure that I have observed several times here during the last few weeks.

First, a brief discourse on boundary layer (BL) structures. The afternoon BL is usually, but not always, well-mixed in both potential temperature (theta) and in moisture mixing ratio (q). Such BL layer structure is illustrated in the Phoenix 00 UTC sounding from last evening (Fig. 1) and in the TWC 00 UTC sounding (Fig. 2), ignoring the dry spike in contact layer. TWC uses the new Sippican sonde, whereas, Phoenix uses a Vaisala sonde with a different type hygristor. Both afternoon soundings depict a well-mixed BL extending from just above the surface to about 750 mb.

When winds are light and there is little advection or turbulent mixing during the night (the situation present over southeastern AZ during the past night), a cool and stable nocturnal BL develops near the ground, with the residual BL from the previous afternoon remaining in place above the nocturnal BL. The Phoenix 12 UTC sounding this morning (Fig. 3) indicates a residual BL present from about 850 to 700 mb.

However, the TWC 12 UTC sounding this morning (Fig. 4) indicates a much different structure aloft over Tucson this morning. Note that the theta profile indicates a residual BL aloft in about the same layer as found in the Phoenix sounding. However, the structure of q does not indicate a residual BL in the moisture field. Above the nocturnal BL q decreases steadily from about 12 g/kg to about 8.5 g/kg at 750 mb and then jumps up to 10 g/kg at 700 mb. This structure is physically very suspect, although I can not prove that the q values are bad, I feel strongly that they are.

Based upon the TWC afternoon sounding at 00 UTC, one would expect to find a residual BL well-mixed in moisture, as in the Phoenix sounding, with nearly constant q values of about 10 g/kg. The Sippican sonde seems to have responded slowly to the abrupt change in q above the nocturnal BL decreasing steadily from 900 to 750 mb and then jumping back up to the expected value of ~ 10 g/kg at 700 mb.

Interestingly, although I am personally convinced that the TWC morning moisture profile data points are erroneous from 900 to 700 mb, the sounding's total IPW agrees very well with the GPS IPW. Thus, at times the GPS-derived data may indicate that a Sippican sounding is accurate wrt IPW, even though there may be serious problems within the details of the Sippican data.

Errors such as the ones likely present in this morning's TWC sounding can have serious implications if one is trying to forecast the likelihood of strong convective storms.

Weather Update for Next Couple of Days

The last week has been very interesting with very high IPW combined with very warm middle level temperatures. It has seemed like Central America. Several very heavy rain events occurred with little or no cloud to ground lightning. There were three fatalities here in the Tucson area due to flash flooding.

Yesterday was quite interesting as skies cleared and IPW decreased steadily. Winds aloft here in southeast AZ were very light. With the abundant sunshine, a well-mixed afternoon BL built up to about 750 mb. So, the drying was apparently a result of weak advection plus subsidence - particularly from 700 to 400 mb. The BL has retained fairly impressive moisture, and dewpoints remain high in the SE part of state.

The TWC sounding has suspect structures this morning - more on this in a separate blog post later this morning - but it appears to me that with heating and slow deepening of BL, coupled with at least some degree of cool advection in middle levels, deep convection will return very quickly. This afternoon we may see Cbs over the nearby mountains. Then things get more complicated.

There is a substantial tropical wave moving westward into the eastern Pacific. Very impressive convective complexes occurred over the lower GoC and further south last night. Thus, with falling pressures in lower Colorado River Basin and southern AZ (about 2 mb during last 24 hours), southerly winds, and moisture advection, should increase up the GoC.

The NAM has had great difficulty last two weeks over Mexico. Disturbances persist in analyses and forecasts with apparently a lot of latent-heating induced spinup leading to stronger middle level winds in the model than have likely been present in the real atmosphere. The lack of observations over most of Mexico lets the model feedback on itself and develop structures that may or not be real. For example, this morning's run takes the main tropical wave to the west-northwest, but it also breaks off a piece to the north up the GoC - winds around this feature may again be too strong, but it is certainly an interesting situation worthy of careful monitoring.

Meanwhile, I'm really enjoying the return of some sunshine to the desert!

Sunday, July 29, 2007

Spectacular wall cloud, heavy rain, and wet downburst move across north Tucson (07-28-07)

Heavy storms with flooding rains and damaging downbursts hit Tucson again early yesterday afternoon (Saturday 07-28-07).

On the north-central side of town, where we live, a storm cell moved southward from the west end of the Catalina Mountains. This cell had a spectacular wall cloud, see:
(NOTE: file size = 91.3 mb)

and Photos 1, 2, and 3. I took the first two from the house looking north at around 12:50 pm MST and tried to get the entire wall cloud/mesocyclone in the view. Photo 3 shows the east side of the wall cloud from the UofA's "Arizona Webcam." (This cam looks due north; the vantage point is a window in the Gould-Simpson building.)

A massive wall of rain developed to the rear and to the east side of the wall cloud. An associated wet downburst took down limbs and entire trees in a region along Ft. Lowell stretching 2 to 4 miles east-southeast from our house. I was out at sunrise taking some photos of the damage. Two large mesquite trees at Ft. Lowell and Dodge fell, taking out the power lines at intersection - police were still directing traffic through that intersection at 5 pm last evening. Photos 4, 5, and 6 show photos of downed trees in the area mentioned above.

Rains of 2 to 3 inches were measured over much of the Tucson metro region causing serious flooding, high water rescues, and the usual problems caused by stupid motorists. The news story at:

has a nice slide show focused on the flooding and water damages, plus a helicopter rescue.

Thursday, July 26, 2007

Heavy rains and damanging winds hit Tucson metro area

Heavy and severe thunderstorms hit Tucson on Monday and Tuesday, the 23rd and 24th of July 2007.

Have returned after 3 days in Boise, Idaho. Saw the indications of serious urban flooding that occurred last couple of days as we drove from airport to house. Quite a few limbs and trees down here and there all the way from airport to our neighborhood. Neighbors seemed to think that winds were worse with the Tuesday storm. Monday storm led to 4 severe wind reports and Tuesday's storm produced 3 severe reports at SPC - including a gust to 63 mphat DM AFB.

When I walked this morning, I noted many limbs and a couple of trees down - but of course, I don't know if the damage occurred Monday or Tuesday. Workers were sawing up large sycamore limbs that were downed at Campbell and River (my guess would be on Tuesday).

Newspaper stories indicate that there was fairly widespread damage acrossparts of the metro area on both days - but the severity seems to have beengreatest on Tuesday. Stories for anyone interested are at:


The second story has a nice slide show of storm events from both Monday and Tuesday. A good amount of rain accumulated in our gauge while we were gone - 1.94" Guess I should leave more often, or perhaps it's the combined effect of Mullen and Maddox both out of town? I took a quick look at the soundings from Sunday morning (the 22nd) through this morning (the 26th). Given that the atmosphere has been very moist and that winds have been very light through most of period, I find it distressing that the evening soundings continue to exhibit a drybias, see:

With the moist atmosphere, there have been numerous sounding problems due to wetting of the Sippican thermistors. I note bad layers in the following: 22/12Z; 23/12Z; 24/00Z; 24/12Z; and 25/12Z; with 25/00Z suspect. It's hard to have a very high degree of confidence in these "new and improved" upper-air data!

Today's morning sounding continues to show light and variable winds in much of troposphere, except that upper-levels have some flow and also indicate substantial difluence over SE AZ - so large-scale upward motion may help things along a bit today.

Monday, July 23, 2007

Off to Idaho . . .

I will be away until Thursday - we are flying to Boise ID in
a couple of hours. Will have camera in hand, since several weak
short waves, and moisture from the SW, are moving up the
back of the 500 mb anticyclone toward ID, i.e., a "Ring of Fire"

Coverage of the Mexican supercell is at end of the third post down.

Sunday, July 22, 2007

More severe storms on 21 July 2007

Prepared at 8 PM MST Sunday July 22, 2007

Although Friday the 21st of July was a "down" day in the local Tucson metro region, intense storms returned on Saturday July 21st late in the evening (good Friday call by Pat Holbrook!). Severe storms with heavy rains and downbursts moved in from the E to NE, producing very heavy rains of more than an inch and downburst winds over much of the metro area. Except of course here at the house, where we had mostly winds and lightning and thunder followed by very light rains after midnight.

A measured gust of 56 mph occured at DM AFB, and TUS reported a gust in the 40's. Most of the downburst damage occured on the east and south sides of the metro area. I drove down Grant and Kolb this morning and observed that there were a number of trees down in a large Target parking lot at Kolb and Grant, with sctattered trees and limbs down at least to south of Kolb and 22nd - about four miles- DM is about another 2 miles to the south, so I suspect that there was more wind damage south of where I drove.

Newspaper reports indicate that power poles were downed in the south metro area just north of the Tucson airport and that power lines were downed in the area around Alvernon and I-10, a few miles ENE of the airport.

I was able to get a photo of this storm as it was moving into the metro area. I took this shot looking about due east from the front of my house at about 7:15 pm MST.

Storm reports for 19 July 2007

Prepared 7:00 pm MST 22 July 2007

As things turned out, the 19th was a very active storm day in SE AZ - refer to previous post.

There are many severe events documented under storm reports at the SPC page.

Here at the house, the event was mostly wind and dust followed by some nighttime trailing rain.
There was a very bad dust storm here right before dark. The Catalina Mountains were totally obscured when the gust front blew in - I don't think that I've observed that before. At atmo the roof-top anemometer registered gusts to ~ 75 mph. Unfortunately, there was not enough light for me to get photos.

In Phoenix, Skyharbor airport reported gusts to 55 mph. There was a fatality due to power lines downed by the outflow - BUT, although I have seen numerous newspaper accounts of this death that occurred after the storms moved through, I don't find any severe storm reports at SPC.

However, the most amazing storm report for the 19th was copied to me by NWS forecaster Jeff Davis. A very severe, westward moving supercell ocurred in Mexico, just south of the border.

It hit the town of Cananea (see map), and produced, at a minimum, a spectacular hailstorm. The Tucson NWS Doppler radar documented an impressive mesocyclone with this storm. Since the storm was moving toward the WSW, the mesocyclone was located on the right flank of the storm, i.e., the north flank of the storm. The four-level reflectivity product and the four-level
Doppler velocities indicate the intense nature of this storm a bit after 00 UTC (5 pm MST).

Thursday, July 19, 2007

Big severe storm day today in AZ?

Prepared at 8:00 am MST, 19 July 2007

The summer thunderstorm season in southern Arizona has been very slow and sparse to date - except in the far south borderlands. The last few days have been characterized by little CAPE at low elevations, with storms mostly clinging to the mountains in the Tucson area. The low-level moisture levels have been adequate to support some storms, and it has generally come from weak pushes of higher dewpoint air into southern AZ, some nice outflows from storm complexes to the east and south. these have combined with abundant recyling to keep the IPW values in the 30 to 40 mm range. Yesterday, with stronger steering-level winds finally, a storm cell moved off the western end of the Catalina Mountains and produced a wet downburst in Oro Valley. Lots of thunder and wind and dust here, and then a brief burst of rain that left 0.05" in the gauge. We still await a serious push of deep sub-tropical moisture into the state.

But, lots of interesting things are finally happening - a large, Sonoran MCS decayed over the central GoC this am and it appears to have started what will finally be a serious push of very moist subtropical air into southern AZ Doppler radar VAD winds at Yuma show nice SSE winds up to 4,000 ft. The upper-level inverted trough over northern Mexico appears will affect southern AZ late pm - early night today with nice difluence aloft. By tomorrow evening it will be right overhead, with the difluence weakened and shifted to NW AZ. During this period there is upper-level ridging over a subtropical circulation that is located south of the mouth of GoC.

This system is predicted to strengthen considerably by the NAM and may becomea TS? Regardless, it is perfectly positioned to intensify the surge of moisture into AZ for the next 60 hours!

The NAM suggests a not very favorable upper-level shear profile this afternoon with easterlies of nearly equal strength from 500 to 200 mb, but everything else looks like it's coming together, and the last two days the model predicted winds have been erratic over this corner of state.

So which day will be the big day? I'm going to go with:

Likely big severe tstm day today, and then two days of good, heavy rain storms.

Sunday, July 15, 2007

Slow start to summer thunderstorm season around Tucson

Prepared at 8:30 am MST 15 July 2007

Yet another day of no storms yesterday in the lower elevations of southeast/south-central AZ. Dry BL air again advected in from the NW, but not as severely as the last couple of days.Quite a slow start to the storm season around here - although Art Douglas has been reporting on the abundant rains to the south along the borderlands.

Misc. points of interest this morning.

Precipitable water and dewpoints are down relative to 24 hours ago.

It's hard to find possible CAPE in the morning sounding, which was about 3 mm on the dry side vs GPS. But there are mid-level buildups and light showers drifting by, so there is a bit of elevated CAPE around.

Winds aloft are very light indicating heavy rain potential, if storms do develop.

Surface pressures have fallen about 3 mb, relative to 24 hours ago over the southern half of state.

The NWS POPs for today are the lowest (10%) of the last several days. However, one of the showers passed over our house between 6 and 7 am MST (I know the timing for certain since it caught me in middle of a morning walk), and actually produced 0.02" of rain in the gauge. Thus, today is the 4th day in July that there's been measurable precip here at the house (grand total to date for July is only 0.26").

The ESE-WNW cloud band that has been south of us the last couple of days is now directly overhead. It appears to be co-located with a weak 300 mb trough/deformation zone. Heavy rains have been associated with this feature to our south yesterday and day before.

The NAM 500 mb analysis at 1200 UTC this morning says that the trough over central TX curls back north over northern MX as a weak inverted trough that extends north into the cloud band mentioned above. I can't see any indication of this feature, but it's again something that the model says is in the great data void to our south. The models do very interesting things with the Texas trough during the coming five days!

Certainly hope that there's some persistence associated with the cloud band and that the heavy storms shift northward with it today.

Monday, July 09, 2007

More on sounding analysis post-NWS RRS

On Saturday morning Jon wrote:

"The emphasis on the AFD and SPC forecasts, however, was whether coverage of the *severe* potential would be greater on Fri compared to Thu. Sure, it was more convectively active on Friday over Thursday. But, it is tough to say, at this point, on the coverage of severe thunderstorms based on no mention of such in media, print or LSRs from Friday. Have you seen any bonified severe reports from Friday?"

Actually, while there was lots of severe storm verbiage in the FD discussion the bottom line, as I interpreted it, had to do with general coverage of storms and POPs, which were left at previous levels. On Friday storms formed early; rained and anviled out by late afternoon; and there were no severe storm events, even though coverage of storms was greater. This often happens in the Tucson area, but it was not clear to me from the morning sounding that Friday was going to be an early storm day. Which leads to the issue of importance, as Jon stated:

"I agree--sounding assessment is tricky with the known problems. Thank goodness for PWAT sounders across the region."

I think that "tricky" may be an understatement. Consider this morning for example: The TWC sounding indicates IPW of 41mm with CAPE of well over 1000. These are quite high values for here and may (?) indicate much more storm potential today vs yesterday. The dilemma is that it appears that IPW is 5 to 6 mm too high wrt GPS IPW. The question is how does one know how to modify the "wet" Sippican data this morning? Where exactly is the phantom moisture that needs to be subjectively removed? How will this wet sounding affect the morning model runs?

Last evening the situation was just the opposite. The high resolution WRF model forecast indicated moderate CAPE at TWC at 0000 UTC, but topped by a layer of considerable CIN. However, the TWC sounding for that time indicated no CAPE whatsoever - but comparison of the IPWs indicated that last evening's Sippican data were about 7 mm too dry. Again the dilemma is: how do we know what the structure of the real atmosphere was?

I guess that I must admit that I am puzzled as to why there is so little reaction by any or all who are in atmospheric research and/or weather forecasting who use upper-air data or derived products. As for me, I am very angry and frustrated by the damage that's been done by the RRS program to the quality of the US upper-air sounding data!

Friday, July 06, 2007

Sounding Analyses When Data Are From Unreliable RRS Sippican Sondes

Prepared 4:00 pm MST on July 6, 2007

I think that the Tucson NWS upper-air soundings from yesterday afternoon and from this morning illustrate several problems that forecasters, and other users, will have with the data from the unreliable Sippican sondes being used operationally by the NWS RRS program.

First, let's examine the 5 pm MST (0000 UTC) Tucson sounding from yesterday - See Fig. 1. This sounding was taken on a very hot afternoon, about two hours before severe thunderstorms moved into the Tucson metro area. Things of importance:

  • The well-mixed adiabatic boundary layer (BL) reaches to 600 mb in the temperature profile. A layer of steep lapse rate is just above, reaching from 600 to 450 mb, i.e., an excellent thermal situation for high-based convection. Winds in the thermal BL are light and variable, meaning that advective changes were minimal, until the storms moved into Tucson.

  • The moisture profile from the 1st data point above the surface to 700 mb appears to be too dry in the extreme. There is no physically realistic BL captured in the Td profile. There should either be a BL well-mixed in moisture or, if shear at 600 mb was mixing dry air downward into the BL, decreasing mixing ratio with height would be expected.

  • Computed CAPE for this severe thunderstorm proximity sounding was zero.

The analysis and forecasting dilemma is obvious. Since the Sippican sondes tend to measure Td (RH) too low, we have no idea what the actual BL moisture structure was
prior to the thunderstorms and macrobursts.

Second, let's look at this morning's sounding - See Fig. 2. Things of importance:

  • The moisture profile bears no resemblance to that observed the evening before. Now we must ask whether we should accept this profile as accurate.

  • Note that if this profile becomes well-mixed (in T and q) during daytime heating to 550 mb, there would be at most a tiny sliver of CAPE. There is advection from the SE to consider however.

  • The GPS IPW at the time of the sounding was about 6 mm greater than that of the sounding. This calls into question, again, the accuracy of the Td profile.

Given the unreliable character of the Sippican moisture measurements, it is not clear how the forecaster, or other users, can actually diagnose what is the real potential for convective storms. The morning forecast discussion from the Tucson NWS Office, based to some degree on this sounding, concluded that:


Interestingly, here at the house, there have been thunderstorms and occasional showers since about 2 pm. Updraft bases appear to be at about 600 mb and an intense downburst appears to be in progress a couple of miles to the east. I suspect that the morning sounding was dry and that there has also been some additional increase due to advection. This combines to make this afternoon much more convectively active than yesterday.

Damaging macroburst(s) hit Tucson metro area last evening

Prepared at 10:30 am MST Friday July 6, 2007

This post will document the thunderstorm and macroburst(s) that moved across Tucson last evening between about 7 pm and 8:30 pm MST (0200 to 0330 UTC). I will follow this with a second post examining the RRS Sippican soundings from the Tucson NWS site. The second post will examine how difficult it is to diagnose the storm potential and local environment with unreliable sounding data.

There is one severe storm report posted for Tucson at the SPC storm reports page this morning:

This area of town is just to the west-northwest of our house. On a walk this morning, I observed and photographed trees and moderate limbs down, and everyone I encountered talked about the vicious wind storm last evening. When I drove out to have some car repairs done I observed numerous moderate limbs and trees down; several intersections had damage to the light poles and police were directing traffic. I only observed one building that had roof damage (at the intersection of Campbell and Grant). This was in north central Tucson and not covered in above report. I am told that the atmo roof-top anemometer measured a gust to 80 mph; this is near the downtown and just to the northeast of the NWS Office. The newspaper reports four different power outage areas scattered over a large part of the metro area from 0200 UTC until 0330 UTC. Obviously this was a significant severe thunderstorm event!

The following photos document the storm and a bit of the damage:

Photo 1 - taken from a campus web cam at 7 pm (0200 UTC,) looking north toward the Catalina Mountains, shows the very high-based updraft over the mountains. There is a slight bit of blowing dust visible, but this was coming from a different cell off to the east.

Photo 2 - shows the updraft from our house, at 0230 UTC, over the west end of the Catalina Mountains. Note that a precipitation shaft has developed and is reaching the ground. At this time the storm was characterized by frequent cloud-to ground and in-cloud lightning.

Photo 3 - shows the precipitation moving off the west end of the mountains toward the south. This photo was taken 3 minutes after Fig. 2.

Photo 4 - shows a large salt cedar limb down. Figures 4, 5 and 6 were taken within two blocks of our house to the northwest, the east, and the south.

Photo 5 - shows large gum tree limbs down in front of a house.

Photo 6 - shows a small paloverde tree that was uprooted.

When the macroburst struck at our house the period of strong gusts lasted about 20 minutes. I estimate that we had maximum gusts of 40 to 60 mph during this period. The strong winds were initially from the north but, after about 15 minutes, switched to the south. I saw some trees down from south winds, but most were downed by the initial north winds. We had a trace of rainfall accompanied by blowing mud.

All in all, a quite a spectacular start to the summer thunderstorm season in the Tucson area!

Thursday, July 05, 2007

A very complicated weather situation

Discussion prepared 1530 UTC 5 July 2007

Last evening we were able to see, from Tucson, widespread anvil and even some convective towers in the distance from north to east to southeast. There were some impressive storms over, and near, far east and southeast Arizona and these produced outflows that have affected all of southeastern Arizona during the night - increasing dewpoints and precipitable water, while keeping low temps very high (Tucson's "low" this morning was 87F). Douglas reported a severe thunderstorm wind gust as several outflows passed there. These storms were associated with a weak 500 mb shortwave through that has come over the top of the western US ridge and moved south-southwestward, to the west of the amazingly persistent cyclone that has been anchored over the southern Plains for several weeks. This cyclone, which again this morning seems to have taken on warm-core tropical characteristics, is forecast by the models as (and appears to be) breaking apart with pieces going several directions. The part that moves into northern Mexico does not really swing across southern Arizona with middle-level winds forecast to remain northeasterly though 48 to 72 hours. See the following 500 mb analysis and forecasts from the NAM:

The morning upper-air soundings at Tucson and Phoenix have extremely deep residual boundary layers form yesterday. Tucson's old BL extends to 450 mb this morning! So, even if low-level moisture continues to increase, there will only be small CAPE available at low-elevations for very high-based convection this afternoon. This is a perfect setup for severe downbursts and strong outflows from more intense mountain storms that will try to move into the deserts. The Phoenix sounding is similar.

So, a key question for tomorrow appears to be: Will low-level moisture continue to increase slowly due to evaporation and recycling OR will deeper GoC moisture push in below 850 mb, giving the precipitable water a real kick from south of the border? Yuma appears to be experiencing at least a moderate southesterly push of moisture this morning, similar to the past several days. The KYUX Doppler winds - see the VAD display available at -

indicates that fairly strong SSE winds extend up to about 3000 feet at this time.

My feeling at this time is that the piece of the Texas cyclone that pushes off southwestward across the southern GoC will be strong enough to trigger a significant low-level surge of Gulf Moisture northward into Arizona after midnight tonight. Thus, I anticipate that the summer thunderstorm season is off and running, and that tomorrow will bring increased CAPE and more extensive storm activity across lower elevations of south-central and southeast Arizona.

Monday, July 02, 2007

Additional Comments on the NWS RRS program

My webpage comments on the NWS RRS program have been posted on the Roger Pielke Climate Science weblog

There have been several comments and questions posted at this site as follow:

Question: How many other sites have changed sondes and rendered breaks in seemingly good time series?

The site changes have been documented according to NWS procedures. The problem is that the announcements are not easily seen by many in the data user and research communities. I hope that NWS systems operations people will find ways to improve the dissemination of information about changes in observing systems to all external users.

The new sondes, as per Fig. 1 map shown at, are now being used at a significant percentage of the NWS upper-air sites. Thus, because of the unreliable temperature and humidty sensors, more noise is being introduced into the long-term time series for, eventually, the entire US upper-air network.

I mistakenly did not indicate on Fig.1 that KOUN is now using the Sippican sondes. As of today, KSLE began using the new sonde.

Question: The purpose of the move was to? What do radiosondes measure and how is it used by weather forecasters?

The purpose of the Tucson move was apparently to save money, since continuing the observations at the airport required a service contract. That contract was terminated. The move will eventually save the NWS money, even though the new sondes cost twice as much as the ones being discontinued.

Simply put, radiosondes measure temperature, humidty and winds from the surface into the stratosphere. These data feed into the numerical prediction models used by all weather forecasters. Unreliable observations will affect the performance of these models. See comment # 5 at the Pielke site also.

Question: Who is responsible for this program?

Those responsible for the RRS program and the operational implementation of unreliable sondes are apparently the high-level managers of the NWS Office of Operational Systems (OOS). The Director is John McNulty

The OOS branch responsible for upper-air operations is the Field Systems Operations Center. The Director of this branch is John Van Kuren

Sunday, June 24, 2007

The Madweather Blog is currently inactive . . .

The Madweather Blog is currently inactive, as is the monsoon season in southeastern AZ. Katie and are I discussing whether to continue the Blog, or to focus this summmer on more detailed posts on the Madweather web page. I have a new post at regarding the NWS Radiosonde Replacement System (RRS) program and serious data problems from sites using the new Sippican sonde. Please share this url with anyone who might be interested. Bob