Severe Weather Discussion 2007-9-2

Severe Weather Discussion for May 4 – 8, 2007.
Valid: 05/03/2007.

Highlights:

– Severe thunderstorms are possible in western Oklahoma on Friday, but confidence is low.

– Active severe weather day is expected across western Oklahoma into the Texas/OK Panhandles on Saturday.

– Severe thunderstorms are possible each day through Tuesday, at this time confidence is too low to pick a day that has more potentially than any other.

– Chase Status increased to Level 2.

Discussion:

Little change to thinking from Tuesday. Evolution of the weather situation for this weekend into next week is very complex due to the presence of a closed/cutoff low in the SW U.S. and a 582dm ridge in the eastern U.S. Said low should hang around for several days, potentially moving northeast around Tuesday. 00z ECMWF is a little different than the GFS on how this system will evolve and makes the forecast rather frustrating.

On Friday, models remain consistent on developing high instability values across the region as mid 60s dewpoints are in-place. Current indications are that CAPE values will be 3000 – 4000 J/Kg along the dryline Friday afternoon. Mid-level winds will be favorable for severe thunderstorms, however a strong cap will be in-place across the region. The dryline should be slightly east of the TX/OK border. Models show little QPF Friday afternoon, but I wouldn't be surprised if one storm developed. Anything that does go will be severe.

Saturday looks very interesting with improving wind fields across the area and high instability. NAM CAPE values are again reduced in favor of the GFS. Not saying it can't happen, but I'm not biting on 5500 J/Kg CAPE. GFS is around 3500 J/Kg and this looks good to me. Both models develop QPF on Saturday and it looks like a wild day across the region. As such, the Chase Status is increased to Level 2.

Beyond Saturday there is just too much model disagreement on the evolution of this system. NAM has more veered winds aloft than the other models, which would seem to provide a decent severe threat for the region again on Sunday. The downside is this same model develops lots of QPF over the area during the day Sunday. Tough call on it and not sure how much rainfall will occur given what should be a strong cap. Either way, the next week seems to continue an active severe weather season for the region. Question is, will Oklahoma finally get in on the action…

SPC already has a slight risk up for KS/NE tomorrow and this looks good. They may extend it down into TX/OK, but the threat is rather conditional. The Day 2 for Saturday should get a moderate for the eastern half of the panhandles into western Oklahoma and northward to Nebraska. Some part of that area may get a higher risk depending on the ultimate evolution of this event. I'd like to see 250/200mb wind speeds higher, but can't get everything. That may be a limiting factor on the risk area.

Probabilities:

Risk area for any part OK/TX (valid: 05/04 Day 1, Day 2, Day 3):

Slight: 30%, 100%, 100%
Moderate: 0%, 75% 25%
High: 0%, 0%, N/A

Chase Status:

Level 2 – Watching Saturday

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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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