Severe Weather Discussion 2010-5-2

Severe Weather Discussion for April 29 – May 1, 2010.
Valid: 04/27/2010.

Highlights:

– Severe thunderstorms are possible in western/central Oklahoma
Thursday afternoon and evening.

– Severe thunderstorms are possible in eastern Oklahoma Friday afternoon.

Discussion:

Models are in general agreement regarding the evolution of the western
U.S. longwave trof. As with yesterday, there is still considerable
spread among the models beyond Thursday. Additionally, there is
seemingly some intra-model variations, impacting the forecast as a
whole.

The 18z NAM while trending the same has suddenly warmed 500mb
temperatures, thereby reducing CAPE values Thursday afternoon.
Additionally, it no longer develops precip (much south I-70) on
Thursday, even during the night. This no-QPF forecast despite
impressive winds aloft and 500mb height changes around -50 meters on
Thursday. Recent AFDOUN seems to be on the same page, so I guess for
now this will be monitored. Not sure I want to flip-flo too much, so
I'll put Thursday on the wait and see plan, with a low-confidence
forecast. If instability parameters improve, then this would increase
the likelihood of a chase. However, given that Gulf intrusion was
somewhat substantial and moisture return is not expected until
Wednesday night, it may be Thursday before the models are of much use.

Another difficult aspect of this forecast is Friday. Models drag a
cold front slowly across Oklahoma on Friday with eastern sections
seemingly warming up. 12z NAM had copious amounts of precip in this
area on Friday and now is somewhat dry. Wind fields remain impressive
on Friday across the state, such that discrete storms are possible if
surface conditions support such. I'll go ahead and put chances in for
a slight risk on Friday and see what happens.

Saturday looks to be a no-go weather wise as the cold front should be
south of the state but I'm not betting the farm on that forecast. The
18z NAM has it stuck in southeast OK early Saturday morning.

Probabilities:

Risk area for any part of OK/TX (valid: 04/28 Day 2, Day 3):

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

Chase Readiness:

Level 2 – Watching Thursday.

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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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