Weekly Severe Weather Discussion

Severe Weather Discussion for February 2 – 8, 2009.
Valid: 02/01/2009.

Highlights;

– Temperatures near 50F Monday and upper 40s Tuesday, warming to the
upper 50s on Wednesday, mid 60s Thursday, and low 70s Friday.
Saturday and Sunday will be in the mid 60s.

– Thunderstorms are possible Saturday evening into Sunday. Isolated
severe thunderstorms are possible, but nothing worse than small hail
at this point.

– Fire danger will be high much of the week with Thursday/Friday of
particular concern.

Probabilities:

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

Discussion:

One heck of an event last week and pretty darn good on the
forecasting. My compliments to Andy Wallace and Greg Whitworth, the
three of us spent a lot of time talking. The storm put down at least
0.25 inches of water across much of Oklahoma with 1-2 inches in
eastern Oklahoma. Of course much of this was freezing rain or sleet.
35,000 customers were without power at the max on Wednesday. That
number continues to dwindle, although nothing compared to Arkansas and
Kentucky.

Sensible weather this week will be at a minimum much of the week, with
some activity next weekend. Models are in amazing agreement during
the week, with a little divergence towards the weekend.

An eastern U.S. longwave trof is forecast to develop on Tuesday. This
will bring a shot of Canadian air into the region. However, the trof
is displaced well east of the region causing the surface high to
backdoor into the region (move in from the northeast). While the most
intense CAA will be east of the region, the front will cool us down on
Tuesday.

The midlevel flow remains progressive allowing the surface high to
move east on Wednesday. This will start a warm-up, which will last
into the weekend. The only thing holding back warmer temperatures
this weekend will be expected cloud cover. 12z GFS and ECMWF both
send the midlevel ridge to the east and allow (dare I say it) (dare,
dare) a western U.S. longwave trof to develop. This is where the
models differ. The ECMWF loads a lot more northern stream energy into
the trof while the GFS is much weaker. Both of them show a southern
stream shortwave trof. Despite this difference, the timing is the
same for the southern stream system with the GFS naturally a little
faster with the northern stream system. I'm siding with the ECMWF due
to time of year and GFS's tendency to dampen western U.S. systems. No
middle of the road this go around, I'm probably going to get 'had.'

Model BUFKIT data supports 60s on Thursday and 70s on Friday. I'd
think we'd hold the Friday numbers into the weekend but given expected
cloud cover, I'm keeping temperatures down. 12z GFS actually flat
lines temperatures in the mid-60s over the weekend. This really looks
good, although could be wrong especially if the ECMWF's stronger trof
occurs and slows down.

A big plus is the early week eastern U.S. longwave trof will develop
farther east than thought last week. As such, the resulting high will
not totally whack the Gulf or sit there. The Gulf looks to recover on
Wednesday with moisture return occurring on Thursday. GFS BUFKIT data
shows mid 50s dewpoints for Oklahoma and this may be a little
generous, but won't argue with the potential. Additionally, PW values
increase, especially going into Saturday. GFS creates elevated
instability Saturday night into Sunday as moisture return continues,
additionally it spikes surface CAPE values to 500 J/Kg. There isn't
much lift (Omega), but this looks sufficient to introduce a slight
chance of thunder and I'll carry that chance into Sunday. If the
ECMWF verifies, could see a little more widespread thunder. GFS has
little precipitation during this forecast week, but that may change.
It appears that better precipitation chances are just beyond this
forecast period.

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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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