Weekly Severe Weather Discussion

Severe Weather Discussion for December 15 – 21, 2008.
Valid: 12/14/2008.

Highlights:

– Strong Arctic front moving into Oklahoma this morning, will blast
through the state during the day. Temperatures will rapidly fall
immediately behind the front and be below freezing by this evening.
Additionally, very strong south winds will occur ahead of the front
and shift to strong northerly winds behind the front.

– Periods of light freezing rain, rain, and sleet are all possible
Monday – Wednesday. The primary impact area will be northern
Oklahoma. Amounts are expected to be light with impacts mainly to
travelers. Wednesday night and Thursday could see a more concentrated
threat of frozen precipitation, but confidence is low on the potential.

– Temperatures in Oklahoma Monday – Tuesday will be in the 20's.
Wednesday may see temperatures climb to the upper 20's to low 30's.
Thursday is very iffy with a potentially huge temperature gradient
across the state of 30's north to 50's south. Friday will likely be a
little warmer with highs in the low 40's north to upper 50's south.
Saturday and Sunday will be cold with highs in the upper 20s to mid
30's.

– Winter Solstice occurs Sunday (12/21) at 6:04am.

Probabilities:

– Severe Thunderstorms in Oklahoma: < 5%
– Storm Chase: < 5%
– Winter Precip: 25%

Discussion:

Cold front way ahead of schedule per morning Mesonet obs and NWS
morning AFD. I should have gone with Greg's timing, but anyway. In
central Oklahoma we'll squeak out part of the day and then get brought
back to reality this afternoon. Southern Oklahoma can enjoy the heat
a little later. Strong south winds will occur ahead of the front.
Behind the front, temperatures will rapidly fall into the 30's then
20's with strong northerly winds.

Models are in decent agreement regarding the mid-level features much
of this week, in fact the GFS/ECMWF are very close through
Thursday/Friday. However, the surface depictions are horrific.
Everyone is going with the ECMWF's temperature map and of course I've
been picking the colder model the past few days also. For today's run
it is the ECMWF. The GFS is way too warm through Thursday and has
been the past few days. As noted a few days ago, it may take the
Arctic air getting sampled tonight before the models get a clue. This
issue is of major importance as precipitation is expected through
Thursday.

Monday – Wednesday

Models agree that there won't be any one particular time of strong
forcing to cause lots of precipitation in Oklahoma. However, there
will be a few bouts that may cause problems. The first one is late
tonight into early Monday. This is seemingly problematic due to the
nocturnal timing and min in travel. As such, there could be some
travel problems Monday morning across the state. Another small
shortwave trof lifts out on Tuesday across Kansas, with more of the
same as Monday morning. The NAM picks up on this feature real well
and looks like the main precipitation will stay in Kansas with some
impacts in the eastern 1/3rd of Oklahoma. Travel problems are again
possible, but should be limited to northern and eastern sections.

Thursday

Next wave is expected to eject out of the longwave trof position and
move into the region late Wednesday into Thursday morning. This one
has me concerned and I think the GFS is missing the boat here. OUN
hinted at this also and for now will note the potential for a more
robust event than Monday – Wednesday. This will be reviewed in the
ongoing special discussions. I wish I had the NAM through Thursday as
it seems to be doing a good job.

Friday – Sunday

Friday will be relatively nice with highs in the 40's and 50's. Late
Friday into Saturday another Arctic blast plows through the state.
ECMWF/GFS both show this happening and it fits with the mid-level
pattern. As such, temperatures have been lowered dramatically for
next weekend with highs in the 20's/30's. Precipitation chances
Friday – Sunday are currently very low with no impacts expected.

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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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