Severe Weather Discussion for February 23 – 24, 2007.
*Active Severe Weather Event Tonight*
– Widespread severe thunderstorms are likely tonight with the potential for isolated destructive winds. Additionally, isolated tornadoes, widespread damaging winds, and large hail are all possible for central Texas northward to southern Kansas.
– This is a Particularly Dangerous Situation with the potential for destructive straight line winds across parts of Oklahoma. Additionally, there is a small chance of strong tornadoes across north Texas into western Oklahoma.
No change to prior forecast or reasoning. Powerful longwave trof is moving towards the region this afternoon and should start to influence us by early evening. A surface low has developed resulting in strong southerly flow across the region and associated moisture advection. Impressive flow at 850mb and 700mb will impinge on the region later today with 40-60kts at 850mb and 700mb 50-60kts. This will create very favorable speed and directional shear for supercells, with helicity values above 400 m^2/s^2.
Isolated storms may develop this afternoon across the Texas panhandle and SPC has just issued an MD for this potential. They indicate a tornado watch is likely. Dewpoints are in the mid 50s with temperatures in the low 70s in the Texas panhandle. However, in a small part of western Oklahoma, contiguous to the panhandle, clouds have held all day and temperatures are about 6-8 degrees cooler. The best instability is in the eastern half of the panhandle with CAPE values around 1500J/Kg and LIs to -6, per ARPS model. Moisture should continue to stream north with 60F dewpoints not far from Oklahoma. As such, despite the cloud cover, instability will increase; this will also occur as lapse rates increase with the approach of the mid-level trof. Any storms that develop in the panhandle region will be isolated and supercellular. These storms may produce tornadoes, but more likely large hail, as is common with LP supercells.
Later tonight the upper system will move into the region and provide synoptic scale lift along the dryline. By this time the dryline should be in western Oklahoma. A squall line should develop as the cap at 650mb is removed. Moisture limitation may reduce the overall threat tonight, but it is best to err on the side of caution and use enhanced wording. I continue to feel that the straight line wind threat is the main issue tonight. Hail should be limited once the squall line forms, although isolated tornadoes will continue to be possible.
Level 1 – Normal
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