Weekly Severe Weather Discussion

Severe Weather Discussion for March 2 – 8, 2009.
Valid: 03/01/2009.

Highlights:

– Temperatures on Monday will be in the low 50s, upper 50s Tuesday,
mid 70s Wednesday, mid 80s on Thursday, upper 70s Friday, mid 70s
Saturday, low 70 Sunday.

– Severe thunderstorms are possible Saturday and Sunday, most likely
area will be eastern half of Oklahoma.

– Extreme fire danger is expected Wednesday and Thursday, but will be
high all week.

– Time change 03/08/2009, move clocks forward one hour at 02:00 as we
go from CST to CDT.

Probabilities:

– Severe Thunderstorms in Oklahoma: 30%
– Storm Chase: 15%
– Winter Precip: < 5%

Discussion:

Interesting week ahead as several weather events appear possible.
Extreme model disagreement makes the latter part of the forecast D5-D7
difficult and low confidence. Unfortunately it is when weather
impacts are possible.

The Gulf is getting violated in ways I don't want to imagine due to a
very impressive early March Arctic cold front. Dewpoints are in the
single digits in Oklahoma with temperatures in the low 20s expected in
Oklahoma City tonight. The record low is 6F, so that is not in
danger. Previously stated Gulf whacking will have two impacts this
week. 1) High to extreme fire danger will be likely much of the week
and 2) precipitation chances will be nil through Friday as the Gulf
recovers. The bright side and I use the word loosely, is that the
resultant surface high center will not move through the Gulf. As
such, the whacking will abate by Tuesday with return flow commencing.
Of course, said return flow will mainly be modified continental polar
air, but hey it will allow the Gulf to start recovering.

For several runs last week the ECMWF and GFS hinted at severe weather
@7th/8th of March. As of this morning the ECMWF went the other
direction and the GFS is flipping a little. The last two runs of the
ECMWF have held to the idea of an eastern U.S. longwave trof with
another significant cold push into the central/eastern U.S. This is
not completely unreasonable, but is a solution not supported by other
model runs. The GFS for the most part keeps a progressive pattern as
southern and northern stream energy move into the western U.S.
Typical GFS biases are noted here as energy is dampened while moving
eastward. NWS offices are going with the GFS and overall it is the
most consistent model and does have support from its ensemble members.
The ECMWF's 180 degree change hurts confidence in its solutions,
although more consistency in the current solution would change that
opinion. Since I only issue this once a week, I'm stuck on picking
model and hence a forecast.

Very amplified pattern will slowly deamplify early this week as the
eastern U.S. longwave trof moves east and a closed low off the
California coast sits and spins. 12z NAM/GFS are in general agreement
with this solution. Since riding will be in-place across the region,
there is no chance for precipitation through Thursday. Meager
moisture return is expected on Thursday with dewpoints creeping into
the upper 40s, mainly in eastern Oklahoma. Dewpoints will remain
quite low farther west. Moisture continues to increase on Friday with
models showing low/mid 50s for eastern Oklahoma. Dewpoints will start
to increase in western Oklahoma, albeit only in the upper 30s/low 40s.

Saturday and Sunday is where the fun begins. 12z GFS from 02/28
showed what is best described as a moderate-end severe weather event.
Since that time the models have greatly varied between severe
thunderstorms and cold air. Since mid/upper 50s dewpoints should be
located in the state Saturday and Sunday, with seasonable jet stream
winds aloft, I'm going 30% on the severe chance. Climatology would
also support this number and the chase percentage at 15%. These are
both low confidence forecasts and if a moderate-end threat develops,
it will be covered by special discussions.

The other thing to note is that Wednesday and Thursday will be quite
warm and the fire danger will be very high to extreme. I'm going with
the NAM temperatures on Wednesday and GFS for Thursday given southwest
surface flow and warm 850mb temps. The surface temperatures are
supported by model BUFKIT data. I don't know what the record high for
OKC is on Thursday, but we'll challenge it.

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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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