Severe Weather Discussion 2009-2-1

Severe Weather Discussion for February 10, 2009.
Valid: 02/09/2009.

Highlights:

– Active severe weather event is expected Tuesday late afternoon into
the overnight hours for the southeastern 2/3rd of Oklahoma.
Widespread damaging winds is the primary threat. However, large hail
and tornadoes are also possible. Depending the evolution of the event
tomorrow, there could be a window for isolated strong tornadoes during
the early evening hours.

Discussion:

Upper system passed the region this morning with widespread showers
across the region. Unfortunately the amount of rainfall wasn't that
great, but any little bit will do.

This morning's system now sets the stage for what may be a rather
active severe event across the southeastern 2/3rd of Oklahoma Tuesday
afternoon and evening. 19z RUC shows moisture being pushed east this
afternoon from southwest Texas to north-central Texas into northeast
Oklahoma. This push will continue for a few more hours as the surface
low lifts northeast into the Great Lakes region. Next shortwave trof
rounds the base of the mean longwave trof Tuesday morning and ejects
eastward during the day. A surface low is expected to spin up in
southwest Oklahoma or northwest Texas during the afternoon hours.
This is in best agreement with the 12z GFS and 17:30z SPC Day 2
product. Favorable Gulf trajectories and close proximity of moisture
means that rapid return flow will occur as a southerly wind component
develops. GFS shows low 60s dewpoints across the southeast ½ of
Oklahoma with mid 50s farther northwest, including OKC. Wind fields
at all levels will be quite impressive and representative of mid
February. However, unseasonable heat and moisture at the surface will
provide favorable instability for severe thunderstorms.

12z GFS is used primarily for this forecast given the placement of its
surface low and overall expected evolution of the event. SPC notes
that convection may occur during the day tomorrow in eastern
Oklahoma/Texas and this would diminish the expected threat. However,
this will have to be monitored tomorrow. GFS CAPE values for southern
Oklahoma into north-central Texas are around 1500-1800 J/Kg with is
collocated with a helilcity max on the 12z NAM. I have great concerns
about the I-35 area north of Dallas to Ardmore and points east
tomorrow afternoon into the evening. SPC's Day 2 moderate seems to
focus primarily on damaging winds as the event matures. However,
early in the event, as a squall line is forming west near Wichita
Falls and San Angelo, discrete storms appear to be likely. As always,
any discrete storms will have tornadic potential.

As the upper system moves into the region Tuesday evening, a squall
line should race across the threat area. Widespread damaging winds
will become the primary threat during the evening hours, especially
across eastern Oklahoma and Texas.

While I don't go back and redo my weekly discussion, I would go much
higher on the severe probabilities at this point. Tomorrow looks kind
of ripe and enhanced wording may be needed. Lots depends on daytime
heating tomorrow. February and March are quite tricky in this regard
and I have a tough time forecasting temperatures sufficient to
maximize this event given mid-February climatology.

Probabilities:

Risk area for any part of OK/TX (valid: 02/10 Day 1):

Slight: 100%
Moderate: 100%
High: 20%

Chase Status:

Level 2 – while not ready to chase, will certainly watch for something local.

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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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