Severe Weather Discussion 2009-7-3

Severe Weather Discussion for October 1, 2009.
Valid: 09/30/2009.

Highlights:

– Isolated thunderstorms are possible tonight and early Thursday for
the western half of Oklahoma. Primary threat is hail to quarter size.

– Active severe weather day is expected across the eastern 1/4 of
Oklahoma Thursday afternoon and evening. Primary threats are
destructive wind, large hail, and isolated tornadoes.

Discussion:

The hazard of forecasting is being wrong and in this case I lost.
Andy will make sure I hear about it for a long time.

The 00z NAM flipped to the quicker GFS solution, so now all three
models agree on the evolution of this system. System of interest is
on the NV/Utah border per morning water vapor imagery. This system
will be pushed eastward by a very strong kicker in the northern jet
stream as an Omega block develops over the eastern Pacific.

At the surface, moisture return is underway with the Oklahoma Mesonet
showing mid 50s dewpoints moving into southwest Oklahoma as of 6:10am.
Low 60s are spread northward across central Texas with low/mid 70s
dewpoints in south Texas. 1016mb line is just west of Houston and
expect this to drift east during the day. As such, moisture return is
expected to continue across the state today and tonight. A muggy
morning is likely on Thursday.

There are no other changes to the forecast other than the speed of the
system. Upper system is still expected to wrap up into a closed low
over Kansas as a vort max moves across the KS/OK border on Thursday
and swings northward around the trof. The rapid progress of the upper
system will push the dryline across much of Oklahoma by 7pm. As such,
the primary risk area is now the eastern 1/4 of Oklahoma. Dryline
passage in Oklahoma City is expected around 1pm on Thursday with storm
initiation between 3-4pm farther east. Strength of wind fields aloft
and rapid eastward progression of height falls may induce a squall
line before discrete storms can develop. However, any discrete storms
will have a tornado threat. The greater threat moving into the
evening hours will be destructive winds associated with the squall
line as downward transport of momentum occurs.

Isolated thunderstorms are possible tonight into Thursday morning
across western Oklahoma as moisture return continues and height falls
occur in response to the incoming medium wavelength trof.

Activity will clear Oklahoma by midnight with Friday being nice statewide.

Probabilities:

Risk area for any part of OK/TX (valid: 10/01 Day 1):

Slight: 100%
Moderate: 90%
High: 0%

Chase Status:

Level 1 – Normal – too far east!

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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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