Severe Weather Discussion – 2008-14-2

Severe Weather Discussion for November 5, 2008.
Valid: 11/03/2008.

Highlights:

– Active severe weather day is possible on Wednesday across much of
Oklahoma, adjacent areas of north Texas, and Kansas.

– High to extreme fire weather conditions are possible Wednesday
afternoon in the southwestern part of Oklahoma.

Discussion:

12z models continue prior trends with respects to the individual runs.
A large trof is progged to enter the western U.S. on Tuesday and
progress into the central U.S. on Wednesday as a closed low develops
over the northern U.S. Timing differences remain among the models
with the GFS quickest and ECMWF slowest. The NAM-WRF is some where in
the middle. I think to keep myself out of trouble, I'm going to side
with the NAM this go around as it seems fair and balanced.

With that in mind, the Oklahoma wind machine has cranked up and will
get even stronger on Wednesday. A surface high remains in the Gulf
and is not progged to leave until Wednesday afternoon. As such, only
modest modified moisture return is expected. Models agree on upper
50s to maybe 60F dewpoints in Oklahoma Wednesday afternoon. Given
temperatures in the upper 70s, models have about 1000 J/Kg CAPE, per
SPC D3. 12z models put a 1500 J/Kg area in north-central Oklahoma.
What there is of a cap should be readily removed by the late afternoon
hours as height falls move into the region, NAM CIN product shows @
-10 J/Kg at 6pm Wednesday.

All that being said, a sharp dryline is expected to form and be
located near HWY 183 in western Oklahoma by late Wednesday afternoon.
This seems to work well with OUN's graphics and SPC D3. And, at this
point no need to get too detailed, we're still 48 hours out. Wind
fields will be quite impressive, which in turn leads to strong speed
and directional shear in this setup. Isolated storms will have a
decent chance to be supercells and given the moisture limitations
probably LP type. However, the greater threat here appears to be
widespread damaging winds as a strongly forced squall line develops in
western Oklahoma and races across the state Wednesday night. The
NAM's slower speed delays some of the strong wind fields aloft, but
not sure how that will play out at this point.

Suffice it to say that a mutli-mode event is possible on Wednesday
starting out with very isolated supercells and ending up a rather long
squall line. SPC went 30% on the probability map and so I'm upping
the moderate chance. Certainly seems like they're focused an damaging
winds.

Probabilities:

Risk area for any part of OK/TX (valid: 11/04 Day 2):

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

Chase Status:

Level 1 – Normal – I'm out of town anyway.

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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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