Severe Weather Discussion – 2007-10-1

Severe Weather Discussion for May 23, 2007.
Valid: 05/22/2007.

Highlights:

– Active severe weather day is expected on Wednesday across western Oklahoma into Kansas. Additional isolated severe thunderstorms are possible across central Oklahoma during the evening. Primary threats for western Oklahoma into Kansas are tornadoes, large hail, and damaging winds.

– Excessive rainfall is possible late Wednesday into Thursday for parts of the state. Thunderstorms, though low-end should continue through the week. This may increase the flooding threat.

– Chase Status is increased to Level 3.

Discussion:

Models are late to the party on this one due to their cold front location progs the past few days. Until this morning, maybe last night, the cold front was expected to be in central Oklahoma Wednesday afternoon with the surface low near Childress. This would remove the surface features from the best dynamics. However, 12z models runs now place the front in Kansas with a surface low somewhere around Beaver County, give or take 50 miles.

Additionally, recent runs of the NAM have really increase instability parameters for parts of western Oklahoma. Values are expected to be greater than 3000 J/Kg across a large part of Oklahoma. This is noted even today with SBCAPE's above 3000 J/Kg per SPC 19z analysis. MLCAPES are between 2000-2500 J/Kg. Moisture continues to flow north as the Gulf is now open and upper 60s dewpoints are inland. Deep layer tropical moisture will continue to spread north into the region overnight with 30-40 kt LLJ. Models indicate dewpoints in the upper 60s with 850mb dewpoints around 16.5 C. Sufficient instability should occur under strong solar heating across the area with a well mixed boundary layer. One caveat is the expected dryline location. NAM is near I-27 and the GFS is near the Caprock. No reason to pick one over the other. I'd lean towards the GFS as the surface low should firm up near Beaver County during the day and allow the dryline to mix east. The NAM keeps a board
surface low over the northern Texas panhandle.

While not particularly strong, winds will veer with high and increase. In fact the parameters from the surface up to 500mb are pretty good with 25-35kts noted at 500mb. The 300-200mb winds are a little weak and could lead to anvil seeding. However, current EML expectations would tend to limit the number of storms and decrease potential seeding. SPC has a moderate risk up with a 45% area from NW OK into Kansas. They also extend the 30%/10% hatched area to Altus. This certainly has my interest given the favorable thermodynamics and surface feature locations.

GFS/NAM both develop convection along the dryline tomorrow afternoon during peak heating. Any discrete storms will likely be supercells with potential for tornadoes.

I'm going to watch the model runs tonight and see if things continue to be favorable. I'm not so sure on a chase tomorrow, but this one looks rather simple and I do think there will be storms tomorrow. Current thinking is Sayre due to easy north/south options. I think the best stuff is going to northwest but the storms will be more isolated I-40 and south, per SPC's probability map.

Probabilities:

Risk area for any part of OK/TX (valid: 05/23 Day 1):

Slight: 100%
Moderate: 100%
High: 5%

Chase Status:

Level 3 – Monitoring Wednesday, looking towards Sayre.

For more information, weather news, weather blog, and chase summaries go to http://www.hook-echo.com.

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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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