Weekly Severe Weather Discussion

Severe Weather Discussion for October 19 – 25, 2009.
Valid: 10/18/2009.

Highlights:

– Showers and thunderstorms are likely Tuesday night through Wednesday
across Oklahoma. Isolated severe hailers are possible, currently
anything more significant is not expected. Isolated showers are
possible on Sunday in western Oklahoma.

– Temperatures will be in the mid 70s Monday – Tuesday, near 70F
Wednesday, low 60s Thursday, mid 60s Friday, near 70F Saturday-Sunday.

Probabilities:

– Severe Thunderstorms in Oklahoma: 5%
– Storm Chase: < 5%
– Winter Precip: < 5%
– Tropical Development: < 5%

Discussion:

Primary feature of interest this week will be a southern stream
shortwave trof progged to traverse the region on Wednesday. Ahead of
this trof on Monday and Tuesday, southerly winds will transport
initially limited moist air into the state but also warmth. By
Tuesday moisture should increase across Oklahoma with low 60s
dewpoints expected early Wednesday. This combined with increasing
lift from the upper system should result in widespread showers and
thunderstorms. These will focus along the incoming Pacific front by
Wednesday afternoon. Currently, instability is expected to remain
limited and hence the severe threat low.

Pacific high settles over the region Thursday and Friday with cool air
both days, but nothing all that cold. Surface ridge shifts east on
Saturday with southerly flow returning to the region and a warmup.
The 12z GFS show a weak southern stream shortwave trof approaching
western Oklahoma on Sunday. Surface moisture will be lacking, but
I've added a slight chance for showers given focused midlevel lift. A
warming trend is likely into next weekend. Hurricane Rick is likely
to make things interesting for Texas this week but should remain far
enough south to leave Oklahoma alone.

Forecast is in agreement with the GFS through much of the week. I
didn't get into the GFS/NAM battle on the upper system for Wednesday.
The speed doesn't seem to be a major issue given expected cloud
cover/rain. Temperatures late in the week follow the GFS's 500mb
pattern with some modifications to the MOS guidance. Overall October
has been a rather cool (literally) month.

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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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