Weekly Severe Weather Discussion

Severe Weather Discussion for January 25 – 31, 2010.
Valid: 01/24/2010.

Highlights:

– Snow is likely Wednesday night into early Friday across at least the
northern 2/3rds of Oklahoma. Accumulating snows are likely and the
potential for a medium-end event does exist. Ice accumulations are
possible across parts of the region also.

– Showers and maybe an isolated thunderstorm are possible Thursday
across southern Oklahoma.

– Temperatures will be in the low 50s Monday, near 50F Tuesday, upper
50s Wednesday, low 30s Thursday, mid 30s Friday, upper 30s Saturday,
low 40s Sunday.

– Slight chance of snow southern Oklahoma late Sunday.

Probabilities:

– Severe Thunderstorms in Oklahoma: 5%
– Storm Chase: < 5%
– Winter Precip: 40%

Discussion:

Models a little clearer on the forecast for this week with the GFS
going nuts on winter precipitation Thursday. Last time it did this,
Oklahoma City got the 14 inches of snow it predicted. 12z
NAM/GFS/ECMWF pretty much say the same thing, although the GFS is a
little faster per usual. I'm going to side a little more with the
NAM/ECMWF especially since the 00z NAM does support the prior runs of
the ECMWF.

Eastern U.S. longwave trof will shift east during the next 36-48 hours
as weak middle level ridging moves over the southern plains. A
southern stream medium wavelength trof will move inland early
Wednesday and across northern parts of Mexico. Around this same time
a closed low will rotate southeast out of central Canada into the
northeast U.S. This will dislodge a 1044mb ridge of Canadian and
probably some Arctic air. Models differ on arrival of this air with
the 00z NAM around 4am Thursday in Oklahoma City and the 12z GFS
showing around midnight. Frontal timing is likely to fluctuate a lot
over the next few model runs, but either way a nocturnal passage
appears likely.

Upper system approaches the region on Thursday will isentropic upglide
over a cold Canadian surface airmass. GFS goes nuts on the freezing
rain and ice pellet precip types Thursday morning. I'm not quite sure
what to make of it and the NAM ends about the time the fun begins. As
such, will have to track the 12z run against the current GFS numbers.
If the GFS is indeed correct, a high-end event will occur. I'm quite
hesitant to forecast such and will stick with a medium-end event.
Ground temperatures will initially be warm, but expected snowfall rate
or freezing rain rate should rapidly overwhelm the warm ground. I'm
not going to get too caught up in the nasty details as they'll likely
change a lot the next few days. I'm throwing in token 5% severe
chances on Thursday for southeast Oklahoma as the front pushes through.

ECMWF phases the upper system with a northern stream shortwave trof by
Saturday morning over Oklahoma. Model progs at 850/700mb RH is quite
dry and no impacts are expected. Another southern stream shortwave
trof approaches the region on Sunday. This system may get close
enough to drop a little snow on the region before the end of the
forecast period. As such, I'll go with slight snow chances. GFS is
dry and has the system much farther north, I'll nod to the ECMWF for
now.

Special discussions will likely be needed starting tomorrow.

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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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