Severe Weather Discussion 2010-7-1

Severe Weather Discussion for May 19, 2010.
Valid: 05/17/2010.

Highlights:

– Active severe weather day is possible across Oklahoma on Wednesday.

– Isolated severe thunderstorms are possible on Tuesday and again on
Thursday, but the threat is low.

– Chase Readiness is increased to Level 2.

Discussion:

Well advertised southern stream trof is expected to move into the
region on Wednesday. There are several caveats with this system, the
primary being thermodynamics. Models are all over the place and there
is little consistency with intra-model runs. The general idea is for
a warm front to be located in the state at some point Wednesday
afternoon. The NAM has flopped around the most on this feature with
the 18z in northern Oklahoma and the 18z GFS along HWY 3. The
question here revolves around expected precipitation Tuesday afternoon
and overnight as an MCS develops in Colorado. The GFS is odd model
out here developing convective feedback along the Red River early
Wednesday. The NAM's precipitation fields are much better and clear
out western Oklahoma during the afternoon hours. The tough part is
how fast we'll warm up on Wednesday. Monday the 10th was a quick
warm-up once the clouds cleared due to no rain cooled air. So, this
will be a consideration on Wednesday. Further, the models way
under-did instability for the 10th with CAPE values reaching 4500 J/Kg
in western Oklahoma. Time of year certainly argues for a rapid
warm-up assuming there isn't a severe MCS or otherwise widespread rain
on Wednesday.

A dryline is expected along the TX/OK border by late afternoon with
rapid development of thunderstorms likely by 4/5pm. Wind fields will
be quite favorable for supercells with sfc-500mb crossover greater
than 45 degrees and 0-3km helicity @300m^2/s^2. 300/200mb winds are
weaker than last Monday, but this isn't always an issue, especially
when the direction is 270 as this tends to limit anvil seeding. Even
though the NAM does show 50kts at 300mb moving into western Oklahoma
at 00z. The NAM will periodically increase wind fields as an event
gets closer and this may indeed happen here.

SPC will likely do a moderate on the Day 2 tomorrow, but I'll keep it
at 75% for now. If we can warm-up, a high-end event is possible.

Probabilities:

Risk area for any part of OK/TX (valid: 05/18 Day 2):

Slight: 100%
Moderate: 75%
High: 0%

Chase Readiness:

Level 2 – Watching Wednesday

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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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