The NWS’ Sounding Paradox

Posted by pmarshwx on 24 Aug 2011 | 2 comments

The NOAA National Weather Service (NWS) Headquarters has issued a directive that all sounding sites in the southern, central, and eastern regions (along with Montana) are to launch soundings every 6-hours until further notice. The idea here is that the additional upper-air data will help improve numerical forecasts of hurricane Irene — and I fully agree. Ultimately, better observations being ingested into the model guidance should help model forecasts, as well as the NOAA National Hurricane Center with their forecast of the all-important question: Does Irene make landfall somewhere along the densely populated east coast of the United States? (I’ve listed the message below for your reading pleasure.)

So what’s the paradox? For years now the satellite community, as well as some inside the NWS, have argued that NWS Radiosonde (sounding) Program should be scrapped in favor of using satellite derived soundings — especially for numerical forecasts!. In fact, due to recent budget issues inside the federal government, every year there is talk of cutting, or drastically scaling back, the NWS Radiosonde Program in favor of satellite derived soundings. So here is my question:

If the satellite derived soundings are so good, why does the NWS feel the need to have 6-hourly launches for the foreseeable future to improve the numerical guidance of Irene?

I happen to work very closely with another national center that I’m sure would love to have daily 6-hourly soundings to help with their forecast responsibilities…

EDIT (0240 UTC, 25 August 2011): Don’t get me wrong, satellites have their place in aiding forecasters. However, nothing can take the place of observations, and the actions by the NWS speak louder than anything I could say.

000
NOUS42 KWNO 242215
ADMNFD

SENIOR DUTY METEOROLOGIST NWS ADMINISTRATIVE MESSAGE
NWS NCEP CENTRAL OPERATIONS CAMP SPRINGS MD
2214Z WED AUG 24 2011

NWSHQ DIRECTIVE TO LAUNCH SIX-HOURLY RAOBS /SOUNDINGS/...

SDM IS HEREBY RELAYING A DIRECTIVE FROM NWSHQ FOR WFO/S
IN ALL OF EASTERN..SOUTHERN AND CENTRAL REGIONS PLUS
MONTANA IN WESTERN REGION TO LAUNCH SIX-HOURLY RAOBS
/SOUNDINGS/ BEGINNING AT THU 25 AUG 06Z AND UNTIL
FURTHER NOTICE.  THIS DIRECTIVE IS TO PROVIDE ADDITIONAL
DATA INPUT WHICH SHOULD HELP WITH MODEL GUIDANCE IN
FORECASTING THE FUTURE TRACK AND IMPACTS OF HURRICANE
IRENE.

$$

STOUDT/SDM/NCO/NCEP

Some Thoughts on the Upcoming “Groundhog’s Day” Storm

Posted by pmarshwx on 31 Jan 2011 | 1 comment

A couple of things I will be watching this evening

• How the cold air interacts with the developing cyclone

The million dollar question (literally) is going to be how the cold air interacts with the developing cyclone. If the cold air plunges more south than southeast, then I would expect the ejecting surface low pressure (and associate low-to-mid-level lows) to move with a more northerly trajectory. If the cold air surges southeast, then the lows will eject with a more eastward component. This has huge implications for who will see the heaviest snows in Oklahoma and southwest Missouri.

The reason for watching how the cold air interacts with the cyclone is the result of how and where the low-level cyclones develop — which on the eastern edge of the “cold-dome”. I strongly believe the surface lows (and associated other lows) will ridge along the edge of the cold dome. Thus, if the eastern extent of the cold air has a more north-south orientation, this is how the surface low will move, placing central Oklahoma in a longer period of heavier precipitation. If the cold air orientation is more southwest to northeast, then expect the heaviest snow to shift east of central Oklahoma, as the surface development will be farther east.

• How the upper-level jet streams interact

Nearly all numerical weather prediction models are forecasting extreme precipitation amounts overnight and through the day tomorrow. It’s a bit perplexing considering the dry ambient environment. This dryness is most likely being overcome by the strong upper-level divergence associated with the ageostrophic response to a couple of a southern and northern jet streak. This strong upper-level divergence results in strong low-level convergence across portions of Oklahoma that will most likely rapidly transport moist air currently in place across eastern Texas, southern Arkansas, and Louisiana. When and where these upper-level jet streams do couple will play a major role in deciding where the heaviest precipitation bands are located.

• How does the precipitation shield evolve overnight

The last several runs of the operational GFS and NAM develop rapidly accumulating snows across eastern Oklahoma with strong low-level frontogenetic forcing. This is in spite of a +0.5C to +1.5C warm nose aloft. This would seem to favor more sleet than snow. However, if lift is strong enough, this might quickly be overcome resulting in 3-4″ per hour snow rates that are currently forecast. Farther west, the 12 and 18 UTC NAM are developing a more classic deformation zone across a large part of central Oklahoma during the late morning and early afternoon hours tomorrow. This deformation zone is more typical of substantial Oklahoma snow falls than the strong, low-level frontogenetic forcing described previously. This large deformation zone is the reason why the NAM has a large area of 6-10″ snow accumulations to the west of the 12-18″+ forecast across eastern Oklahoma.

Also, if a large squall line develops across central Texas and races east too quickly, the squall line might use up a lot of the moisture that is poised to be drawn northward into this cyclone. This would decrease snow totals across portions of Oklahoma, Kansas, and southwest Missouri.

• The evolution of the temperature vertical temperature profile

I hinted at this in a couple of the previous bullets, but how the vertical temperature profile evolves will be crucial in determining snowfall amounts. If a strong warm-conveyor belt does develop overnight, warm air might hang on longer than forecast across portions of Oklahoma. This might lead to an extended period of sleet which would cut down on snowfall totals considerably. However, 1-2″ of sleet, coupled with 2-4″ of snow would be just as bad, if not worse, than a pure 8-12″ of snow.