Severe Weather Discussion 2008-1-1

Severe Weather Discussion for January 7, 2008.
Valid: 01/04/2008.

Highlights:

– Severe thunderstorms are possible across eastern Texas northward to southeast KS/southwest MO on Monday.

– Snow is expected in northwest Oklahoma late Monday.

Discussion:

18z NAM/GFS remain consistent with prior runs and to some extent each other. The differences aren't enough to worry about at this point and some of it can be considered model noise. The over all setup remains the same as a northern stream longwave trof moves across the U.S. System will be rather progressive and this will limit the severe threat for the region due to limited moisture return. However, expected moisture return is still expected to be above seasonable norms.

Cold surface high moved through the region earlier this week and cleaned out the Gulf, pushing 55F dewpoints to the Yucatan. While the surface ridge will move east out the area the next few days the 1016mb line remains west of the area, indicating quality moisture will not return through early Sunday. During the day Sunday a surface low develops in southwest KS increasing the pressure gradient across Oklahoma and Texas. Modified air may still be moving through the Gulf but some higher quality moisture starts to move north. It should be strongly noted that moisture quality this time of year is typically limited. Despite the prior Canadian/Arctic ridge, enough Gulf recovery is expected for common 50F dewpoinits in the eastern half of Oklahoma with an area of 60F dewpoints in southeast OK southward to TX/LA Coastal area.

Strong southwest flow aloft combined with full sun should result in temperatures in the 60s across much of the state. Models are at odds regarding 850mb moisture with the GFS much more bullish than the NAM. No reason to pick one over the other. With cool air aloft, there should be some instability in areas of best moisture return. GFS CAPE values are around 750 J/Kg and this should support severe thunderstorms. One big concern is presence of very strong winds aloft. The 850mb jet is progged at 65kts with 400mb/500mb winds of 100kts. Storms will be strongly tilted and may have a tough time surviving if there isn't sufficient lift. The best area for storms may be on the leading edge of the moisture tongue in eastern Oklahoma as it interacts with the upper system late Monday. All this is a little premature at this point as things may change over the next few days.

While SPC Day 4-8 product indicates they're expecting a 30% area, I'm not convinced right now. I do think robust thunderstorms development is likely with attendant threats. This seems to be in the upper slight risk range ATTM. The next few days will determine if this can raise to the moderate risk level. If the NAM is correct, neither of these would happen as best moisture would remain south of Oklahoma.

Probabilities:

Risk area for any part of OK/TX (Day 3, valid: 01/05):

Slight: 75%
Moderate: 0%
High: N/A

Chase Status:

Level 1 – Normal

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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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