Severe Weather Discussion 2009-3-2

Severe Weather Discussion for March 23, 2009.
Valid: 03/21/2009.

Highlights:

– Severe thunderstorms are expected across much of Oklahoma Monday
afternoon and evening. Monday afternoon the primary threat will be
large hail and isolated tornadoes. During the evening and overnight
hours, a damaging wind threat will be present. The latter may make
this a medium end event and if SPC upgrades it will likely be due to
this potential.

– Severe thunderstorms are possible on Thursday 03/26.

– Chase Status is increased to Level 2.

Discussion:

Admittedly, much of the free world is more excited about Monday's
severe potential than I am. However, I admit I'm having trouble
getting past the model moisture progs. Despite the limited moisture
noted by all the models, dewpoints will still reach the mid 50s in the
threat area Monday afternoon with 10C + dewpoints up to 825mb in
Oklahoma City late Monday afternoon. I do think there is still some
potential for dewpoints to be slightly higher than model progs and
that would certainly help the event. Additionally, the 18z NAM BUFKIT
data has come in a little warmer temperature wise during the
afternoon. the 742 J/Kg CAPE at Oklahoma City looks good and is
accepted.

Models are in remarkable agreement regarding the evolution of the
500mb closed low and subsequent lower level response. I'll abandon my
thinking on the upper system slowing and concur with the model's rapid
eastward progression and closed development. With this scenario the
upper system will miss Oklahoma Monday morning while impacting KS/NE.
Since the low closes, it also slows down considerably. This will keep
strong winds aloft across Oklahoma, providing impressive helicity.
The dryline will be located in far western Oklahoma and will likely
make only limited progress east during the day.

Models show an area of UVV's moving into Oklahoma during the early
afternoon hours. In fact, the NAM/GFS both create impressive UVV's by
7pm across the dryline. So, storm development appears likely. The
primary question here is can discrete cells develop before the squall
line does develop. Given the potential for a squall line with
wdamaging winds, I'm increasing the moderate threshold. The Day 3,
30% area seemed more for wind than anything.

PRIND: Discrete thunderstorms will develop during the mid/late
afternoon hours along a dryline located near the TX/OK border. Storms
may acquire supercell structure as they move northeast. While many
components will be in-place, moisture currently appears to be a
limiting factor. A squall line is likely by early evening, which will
then sweep eastward across Oklahoma.

Probabilities:

– Risk area for any part of OK/TX (valid: 03/22, Day 2):

Slight: 100%
Moderate: 50%
High: 0%

Chase Status:

– Level 2 – monitoring Monday.

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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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