Severe Weather Discussion – 2006-9-1

Severe Weather Discussion for October 26, 2006.
Valid: 10/26/2006.

Highlights:

– Severe thunderstorms are possible across Oklahoma and Texas on Thursday. Primary threats are strong winds and large hail. Isolated tornadoes are possible.

Discussion:

Complex situation for tomorrow and toyed with not issuing one of these. However, looks like I already blew the weekly forecast with the < 5% on the severe probs.

Southern stream system is progged to close off as it digs southward into New Mexico later today. This system is then progged to move east into the region during the day Thursday. Moist air was rapidly returning to the region with greater than 10C dewpoints up to 800mb across the region.

Model progs introduce a big of uncertainity to the forecast for late Thursday as there is lots of opinions regarding the speed of the upper system. The GFS is most likley too fast as it has been for much of the forecast. On the other hand, the NAM-WRF is probably too slow. As with many of the NWS offices, a compromise is a good idea. A big complicating factor is the weak subtropical system progged to lift out early in the day. This system is progged by many of the models to veer the 850mb wind and remove moisture at this level. NAM-WRF is the only model to back the winds during the day as the closed low approaches this region. It is very too to assess what affect the weakening subtropical system will have on low level moisture.

Current indications are that severe thunderstorms are likely across portion of the region Thursday afternoon. Most likely spot will be along the dryline in Texas where moisture values should be greater. Another hot spot should be the warm front in northern Oklahoma. How significant the activity will be won’t be determined until tomorrow morning when the upper air data provides insight into the 850mb level. I tend to think with decent surface moisture and very strong lift, the lack of 850mb moisture won’t be a huge deal. March 17, 2003, is a good case study for this setup.

For now I am raising the chase level. Not too hopeful on going out, but can’t ignore it.

Probabilities:

Risk area for any part of OK/TX (valid: 10/26, Day 1):

Slight: 100%
Moderate: 25%
High: 0 %

Chase Status:

Level 3 – Monitoring tomorrow, northern Oklahoma.

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Common Terms:

AOA = Around or above.
AOB = Around or below.
CAPE = Convective Available Potential Energy.
CDC = Climate Diagnostic Center.
CPC = Climate Prediction Center.
ECMWF = Numerical model run, European Model.
GFS = Numerical model run, Global Forecast System.
LI = Lifted Index
LLJ = Low Level Jet.
NAM-Eta = Numerical model run, about to become the NAM-WRF
NAM-WRF = Numerical model run, the Weather Research Forecast (WRF)
OUN = Norman Forecast Office.
SWODY = Severe Weather Outlook Day 1, 2, 3, and 4-8.
SPC = Storm Prediction Center.
WWA = Warm Air Advection.
00z/06z/12z/18z – Time based on the UTC time scale, z = zulu.

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About Putnam Reiter

Putnam has been storm chasing since 1990 and is a co-founder of Hook-Echo.com. For his day job, Putnam works in emergency management for information technology.
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