Weekly Severe Weather Discussion

Severe Weather Discussion for February 9 – 15, 2009.
Valid: 02/08/2009.

Highlights:

– Thunderstorms will occur Monday morning across a good part of
Oklahoma. Isolated strong wind reports are possible.

– Severe thunderstorms are possible Tuesday night across parts of
central and eastern Oklahoma. Large hail and strong winds are the
primary threats, however a tornado or two looks possible.

– Rain is expected Friday morning across northern and central Oklahoma.

– Temperatures will be in the low 70s Monday and Tuesday. A cool off
on Wednesday to the mid 50s is likely with a warmup Thursday in the
upper 50s. Friday mid 40s, Saturday low 50s. Sunday will be in the
upper 40s.

Probabilities:

– Severe Thunderstorms in Oklahoma: 30%
– Storm Chase: < 5%
– Winter Precip: 5%

Discussion:

What a difference a week makes! Longwave trof has setup over the
western U.S. with a broad and low amplitude ridge just off the Florida
Coast. Several shortwave trofs will eject out of the mean longwave
position during the week. The first one is expected Monday morning
with the second following late Tuesday, the third Friday morning, and
the forth Sunday evening. I've used a blend of the 12z GFS/ECMWF for
timing of the individual shortwave trofs. There is enough agreement
between the models throughout the week to give good confidence that at
least three systems will impact the region and possibly a fourth
before the forecast period ends Sunday night 02/15. The 12z NAM has
been used as a blend through Wednesday, which is my typical forecast
strategy.

Moisture return has been ongoing for two days and only low 50s have
made it into Oklahoma, of course that is still rather exciting.
Repeated cold air intrusions into the Gulf have seriously displaced
higher octane moisture. However, surface ridge now over the Florida
panhandle is expected to migrate northeast and allow trajectories to
become more southeasterly in the Gulf. This should help moisture
increase across Texas Monday afternoon and Tuesday. However, the
system expected tonight will only have marginal moisture to work with.
A squall line has developed in west Texas and this is expected to
continue east during the night.

18z NAM looks a lot better precip wise as the 12z OKC total of 0.25
was flat wrong. I fell for that trick during the ice storm as the NAM
was the worst of the models on precip. Both 12z GFS and 18z NAM show
around 0.6 inches for OKC Monday morning and this looks good. Upper
system will move out on Monday with strong westerly flow at the
surface. No cold air with this, so temperature will remain warm
through Tuesday. Next upper system approaches and moisture rapidly
returns into Oklahoma. I'm modifying model moisture fields to bring
the moisture farther west and north than currently indicated. I'm
also going higher on the severe probabilities for south-central
Oklahoma than SPC per the 12z NAM. Although I'll say the models are
pretty close with mid 50s in OKC Tuesday night. NAM has 0.4 inches
for OKC Tuesday night, which is probably okay. Severe thunderstorms
are likely across south-central and southeast Oklahoma. Current model
progs point to an environment favorable for supercells in these areas.
The event will transition to damaging winds by late evening as
storms become linear under strong forcing. Strength of wind fields
aloft point to a widespread wind threat for eastern Oklahoma into
Arkansas. SPC has 30% for this threat and looks good.

Wednesday and Thursday will be mild and dry as a cold front pushes the
moisture south of the area. Another system moves into the region on
Friday, which the GFS has much weaker than the first two. GFS
indicates enough moisture, albeit dewpoints in the mid 40s, to get
some precipitation. I'm not sure about snow for far northern OK, but
will go 5% since the core of the system will move across this area.
Models show a Canadian high nudging into the region behind this
system, both GFS/ECMWF show this. Model soundings support the lower
surface temperatures, so it does look like a return to winter time
temperatures next weekend. I feel like I'm gonna get had, per usual.
I certainly did this weekend, although I was a little lucky on the
temperature today.

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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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