Weekly Severe Weather Discussion

Severe Weather Discussion for January 18 – 24, 2010.
Valid: 01/17/2010.

Highlights:

– Showers are expected Tuesday evening into the overnight hours, an
isolated thunderstorm is also possible.

– Showers and thunderstorms are expected Friday night into Saturday.
Isolated severe thunderstorms are possible with low-end impacts.

– Temperatures will be in the low 60s Monday – Wednesday, mid 50s
Thursday, 60F Friday, mid 50s Saturday, low 50s Sunday.

Probabilities:

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

Discussion:

Multiple upper systems will impact the state this week as the southern
jet becomes quite active across the southern U.S. Several small
shortwave trofs will move across the region, but the first one of
consequence is due in Tuesday afternoon. Models are in good agreement
on a small but potent shortwave trof to move across the region late
Tuesday into Wednesday. Modified Gulf moisture will return ahead of
this system with the 12z NAM showing 55F dewpoints in Oklahoma and the
GFS 50-55F. Both NAM/GFS runs indicate surface based CAPE values of
250-400 J/Kg early Wednesday. There is also some elevated CAPE around
the same time as lapse rates 800-600mb are maximized. As such, expect
showers and a few isolated thunderstorms as the system passes through
north Texas Wednesday. System is progged by the NAM to be in
northeast Texas Thursday morning.

There isn't much cooling behind this system, so temperatures will not
drop too much. Next system quickly approaches the region with winds
returning to the south by Friday morning. GFS may be overdoing the
moisture push out of the region and under-doing the subsequent return
on Friday. Lack of a ridge in the Gulf the past week has allowed
moisture to recover. While tropical moisture is not expected this
time of year, a little more robust moisture return seems possible for
the system this weekend.

ECMWF/GFS are in decent agreement on a medium wavelength trof moving
into the region late Friday. Both agree that the leading edge of the
upper system will translate northeast into KS/NE Saturday morning,
resulting in the surface low also translating east. What moisture
does return should be pushed east during the day. This appears to
reduce the overall threat of the upper system as moisture is removed
before lapse rates are ultimately favorable for robust convection.
However, this is contingent on the GFS and I'm not willing to bet the
farm on said solution. As such, I have gone with low-end severe
chances in case the surface features end up more favorable, like the
ECMWF, than the GFS indicates. The best action should be farther
south in Texas where the jet stream will be stronger, closer to the
moisture, and more likelihood of sun. Upper system passes and again
there is little in the way of cold air to follow, however there is
more of a ridge.

I went above GFS MOS Monday – Wednesday and close to MOS through the
weekend. The Monday – Wednesday period is in best agreement with the
18z NAM, which has low 60s these days. Overall, it appears that a
very pleasant mid-winter week is on-tap for the region and maybe a
little storm excitement.

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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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