Weekly Severe Weather Discussion

Severe Weather Discussion for January 17-23, 2011.
Valid: 01/16/2011.

Highlights:

– Freezing rain/drizzle is possible Wednesday night turning to snow
early Thursday. Snow will continue during the day Thursday. Best
chances for accumulations are in northeast Oklahoma.

– Temperatures will be in the mid 50s on Monday, upper 40s Tuesday,
near 40F Wednesday, upper 20s Thursday, mid 30s Friday, low 40s
Saturday, and uppers 40s Sunday.

Probabilities:

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

Discussion:

Models are in decent agreement regarding the 500mb pattern this week
but there are some significant difference between them late Wednesday
into Thursday. 18z GFS/NAM seem insist the incoming cold front on
Tuesday will shift east with a warmup on Wednesday, then a much
stronger cold front on Thursday. All of this occurring as a southern
stream shortwave trof takes shape just west of the area as a clipper
type system. The ECMWF wants to insist on the cold air staying around
late Wednesday with frozen precipitation starting earlier than the
other two models. OUN AFD hinted at siding with the ECMWF and I have
also elected to do so. This places my Wednesday high in jeopardy as
GFS/NAM temperatures are in the upper 40s. NAM BUFKIT does show
clouds on Wednesday and this may help keep temperatures down.

The atmospheric setup this week is for continued northwest flow at
500mb. One shortwave trof will intensify just west of the region and
traverse the state on Thursday. Two cold fronts are expected this
week with the first on Tuesday and a second stronger front early
Thursday.

The main interest this week will be previously noted shortwave trof
late Wednesday into Thursday. All models agree on the development of
this system with some differences in QPF and temperature fields. The
ECMWF, as noted above, is colder earlier than the other two models and
the NAM is drier. As always, the answer is somewhere in the middle.
For this forecast I have gone with the ECMWF on temperatures and the
GFS on QPF. Precipitation chances will increase Wednesday
evening/overnight across the state. A strong cold front will be
approaching and should move through the state early Thursday. Initial
precipitation will start out as rain, but should transition to
freezing rain, sleet, and by Thursday all snow. Areas in southern
Oklahoma will remain above freezing longer and hence snowfall may be
limited to later Thursday morning. GFS has a QPF max over northeast
Oklahoma and would seemingly point to 4-6 inches of snow in this area.
I see little reason to disagree and have gone with 30% probs. If
the coverage was greater, the event could very well be a medium-end
event. However, current thinking yields a low-end event with travel
problems on Thursday the primary concern. The freezing rain threat
will be monitored but for now looks to be too transient to warrant
much concern. Special discussions are not anticipated right now.

I followed the GFS MOS Monday/Tuesday and did mine own thing
Wednesday; which I'll probably take a beating but can't be worse than
yesterday. Followed the GFS Thursday-Sunday. CPC blocking pattern
shows an intense blocking ridge in the eastern Pacific. These
patterns typically last two weeks, so maybe a return to more active
weather in late January. A strong La Nina continues in the Pacific
and will likely have impacts on our weather through February.

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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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