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.

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.

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.

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:

AREA FORECAST DISCUSSIONNATIONAL WEATHER SERVICE TUCSON AZ945 AM MST SAT AUG 11 2007 DISCUSSION...THE TUCSON 12Z UPPER AIR SOUNDING INDICATED A MORE MOIST BOUNDARY LAYER COMPARED TO YESTERDAY. THIS ADDED LOW LEVEL MOISTURE COMBINED WITH GOOD SURFACE HEATING SHOULD YIELD MODERATE TO STRONG INSTABILITY FOR THIS AFTERNOON...ESPECIALLY NEAR TUCSON AND WESTWARD.

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!

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.

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!

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:

http://www.atmo.arizona.edu/~leuthold/20070728.mov
(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:

http://www.azstarnet.com/allheadlines/193921

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

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:

http://www.azstarnet.com/allheadlines/193302

and

http://www.azstarnet.com/allheadlines/193084

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:

http://www.gpsmet.noaa.gov/realtimeview/jsp/quicklook.jsp?SITELIST=COT1&SITELIST=TWCB

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.

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"
setting.

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

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).

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.

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.

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!

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:

"KTUS 12Z SOUNDING ANDGOES PW IMAGERY SHOWS MOST OF THE MOISTURE INCREASE SINCE YESTERDAYHAS BEEN AT MID LEVELS WITH SEVERAL DEGREES OF WARMING IN THE500-400MB LAYER. THAT SHOULD COOL A BIT AS AN INVERTED TROUGH OVER NTX TRIES TO EITHER MIGRATE W INTACT...OR SHEARS TOWARD US IN THERATHER FAST BUT DIFFLUENT FLOW ALOFT. WE ALSO HAD A 40KT NE SPEEDMAX AT 500MB THIS MORNING WHICH IS GOING TO HELP IN THE SHEARDEPARTMENT THIS AFTERNOON/EVENING. BUT THE UPPER 40/LOW 50 DEWPOINTSWE HAVE RIGHT NOW ARE NOT GOING TO YIELD MUCH CAPE. SO UNLESS WE SEEDEWPOINTS REVERSE COURSE OR AT LEAST HOLD WHERE THEY ARE...I DOUBT WE`LL SEE MORE COVERAGE THAN WHAT WE HAD YESTERDAY."

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!

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:

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/12/fp0_000.shtml

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/12/fp0_012.shtml

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/12/fp0_036.shtml

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 -

http://weather.cod.edu/analysis/paulradar.pl?YUX

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.

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 http://climatesci.colorado.edu/

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 www.madweather.com, 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 john.mcnulty@noaa.gov

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