Problem Soundings 0000 UTC May 9th

My quick look at the soundings last evening identified two RSS flights that exhibited strongly super-adiabatic lapse rates in shallow layers aloft. These soundings were taken at Birmingham, AL, and Sterling, VA.

Note that the RRS operational procedures indicate that layers such as these should be removed via manual editing by the operator, and provide instructions for how this should be done.

Figure 1 (00Z BMX)

The layer of interest here extends from about 630 mb to 610 mb. The sonde apparently had moisture on the thermistor, and perhaps on the hygristor. When the instrument exited a deep, cloudy layer it encountered very dry air aloft and evaporative cooling of the sensors probably produced the super-adiabatic layer.

Figure 2 (00Z IAD)

The layer of interest here is only about 10 mb deep and is located near 740 mb. The reason for this super-adiabatic layer is not obvious, since the entir atmosphere appears to be quite moist. The sounding apparently did not exit cloud into a very dry layer above. It is possible that the instrument was in a saturated updraft and exited the updraft suddenly. It is also possible that the hygristor did not respond adequately to a layer that was considerably drier than the data indicate.

During the next few months I'll be paying particular interest in identifying soundings in which bad data have complicated the diagnosis of CAPE or potentially caused forecasting difficulties.

If readers note soundings that seem to be candidates, as per above, for closer examination, please feel free to alert me to them. Thanks, Bob bob@squidinkbooks.com

BLOG will be active now for the spring/summer

I am beginning again to monitor the RRS Sippican sounding data, as I start preparing a formal paper. This paper will document the often poor, and physically bizarre, soundings produced by the Sippican radiosondes the NWS has switched to at most sites in the US.

Today's winning example of a strange sounding is that taken at Ft. Worth TX at 1200 UTC.

http://www.rap.ucar.edu/weather/upper/fwd.gif

Cold Cutoff in the Southwest

Yet another success for the long-range models, especially theECMWF, which correctly forecast the development of the cold, midlevel low currently over the Southwest - beginning from about 5 to 6 days out.

The system produced more precipitation than I was expecting, given the very low precipitable water values. Here at the house, I measured 0.29" through 7 am this morning and light showers remain in the area. Low this morning was 33F.

Precipitation yesterday was from convective showers in the cold, unstable air. I did not hear any thunder here at the house. During midafternoon northern and western parts of the Tucson metro area had heavy showers of graupel (AKA snow pellets) and the ground was covered in some spots.

Perhaps some more of this today, before the system moves on east. It's hard to know how unstable it is this morning, since the somewhat critical Tucson upper-air sounding was missing both last evening and again this morning.

The NWS forecast this morning (see below) mentions the possibility of showers, thunder, and sleet. While showers accompanied by graupel may occur, the liklihood of sleet is extremely small, today or with any winter weather event in the Tucson metro area, since sleet results when raindrops fall through a layer of subfreezing air at or very near the surface. Definitions of graupel and sleet are also below.
-------------------------------------------------------------------
Today: A chance of rain showers possibly mixed with sleet, mainly after 11am. Some thunder is also possible. Partly sunny, with a high near 53. South southeast wind 9 to 14 mph becoming west northwest. Chance of precipitation is 30%. Little or no snow accumulation expected.

From the Glossary of Meteorology:

snow pellets (Also called soft hail, graupel, tapioca snow.) Precipitation consisting of white, opaque, approximately round (sometimes conical) ice particles having a snowlike structure, and about 2-5 mm in diameter. Snow pellets are crisp and easily crushed, differing in this respect from snow grains. They rebound when they fall on a hard surface and often break up. In most cases, snow pellets fall in shower form...

sleet or grains of ice, generally transparent, globular, solid grains of ice that have formed from the freezing of raindrops or the refreezing of largely melted snowflakes when falling through a below-freezing layer of air near the earth's surface....

DEVELOPING WEATHER EVENT

Finally looks like we may have some clouds and weather here in SE AZ during the weekend.

The ECMWF and the GFS ensemble members are all pretty much in agreement now, indicating a strong wave digging down the west coast, with the eventual cutoff affecting us from about 96 to 144 hours - from 00 UTC model runs last evening.

There are about 5 waves strung out across the northern Pacific and it's not clear which one kicks up the ridge into AK, forcing the wave down the coast. Obviously all the models have keyed on one of these to be the agent of change.

The models appear to predict about a quarter to half an inch of precip at lower elevations by late Monday afternoon. Uncertainties this far out - how long will the wave affect SE AZ - some model runs keep it more isolated from the main flow to the north; how much moisture will the system pickup (the ECMWF hints at better moisture flowing northward toward the end of the event, while - surprise - the GFS members stay drier). Only 10 of 12 GFS ensemble members predict measurable rainfall at lower elevations in SE AZ during the event.

Current fcst POPs for both TUS metro and also top of Catalinas max out at 30% for Sunday night. PHX has issued a hazardous weather outlook for this event already (see the nice early am FD from PHX). Will be interesting to watch how this event evolves.

Different topic - My total precip for Dec/Jan/Feb here at house was 5.84 inches -not bad for a la nina winter! Actually not bad for any of past ten winters - beaten only (I think) by the 97-98 el nino winter.

BRIEF SUMMARY OF JANUARY 2008

The weather for the winter continued fairly wet and cold here at the house during January 2008.

There was measurable rainfall on only 4 days but the total, mostly from the storms of the 7th and of the 27th/28th, was 1.00 inch. The storm late in the month produced much flooding and runoff after very heavy rains at higher elevations. The Rillito wash is still running today.

After a very cold December (our gas bill for heating in December was the highest ever during our ten years in the house), January was also fairly cold. There were 18 mornings with low temperatures of 32F or colder. Half of these days had lows of 27F or colder.

The coldest mornings occurred on the 18th - 20th with readings of 20F, 20F, and 21F. This morning, the 31st, was also cold with a low of 22F. There was a period of 14 consecutive days from the 10th through the 23rd with lows of 32F or colder.

So, probably another big gas bill.

Appears that February will also start out unsettled with perhaps more rain during this strange la nina winter.

INTERESTING BUT TOUGH FORECAST FOR LATER IN WEEK

Very interesting situation for the next six days as the complex middle level low off of California coast this morning swings around to south and then minors out across the Great Basin, with stronger wave replacing it. There is also a persistent very tight cyclone far off to the WSW that models may be trying to swing around the south end of the larger-scale trough.

This morning's NAM indicates a precip period Wednesday night through Friday morning. Interestingly, the operational GFS (from 00Z last evening) shows little at Tucson during this period. The GFS tends to keep the subtropical moisture to the south as the first middle level low swings around and minors out, while the second system digs in. The role, if any, of the system out around 140W and 30N is not clear in the model forecasts.

The GFS and the ECMWF (both from 00Z last evening) indicate that the second wave will pull the subtropical moisture much further north and provide the most significant event out toward the weekend. The precip forecast of these long range models is fairly different. The GFS indicates the main precip near Tucson to occur Saturday night and to amount to around a quarter to half an inch. Whereas, the ECMWF indicates that the main precip event would also be Saturday night, but rainfall amounts near Tucson of a half to a bit more than an inch are predicted by this model.

So, the summary is that there may be two distinct precip events over southeastern Arizona with the weekend event likely being the more significant one. Will be interesting to watch how this very complex situation actually evolves. Regardless we're definitely having a more interesting la nina winter than one might have expected!

A WET AND COLD DECEMBER 2007 HERE IN TUCSON

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!

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.

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.

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.

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).

http://www.yumasun.com/

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.

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.

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.

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:

http://www.spc.noaa.gov/exper/soundings/

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.

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

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/source/gemlib/mr/mruadt.f
./gempak/include/GEMPRM.PRM
./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