Severe Weather Discussion for December 17 – 23, 2012

Severe Weather Discussion for December 17 – 23, 2012
Issued:  12/16/2012.
Highlights:
–  Showers and a few thunderstorms are possible across central/eastern Oklahoma on Wednesday.  As with last Friday, a severe thunderstorm or two appears possible.
–  Snow is possible late Wednesday into early Thursday, primarily across northern half Oklahoma.  Right now, best guess is less than 3 inches, but will need to monitor.
–  Temperatures will be in the mid 60s on Monday-Wednesday, low 40s Thursday, near 50F Friday, and low 50s Saturday-Sunday.
–  Winter starts Friday at 5:12am CST.
Probabilities:
–  Severe Thunderstorms in Oklahoma:  10%
–  Winter Precip:  15%
Discussion:
Primary interest this week will the Wednesday and Thursday time frame.  Upper system moving over the region tonight will have minimal impacts as moisture is very limited.  Lack of meaningful cold air will result in temperatures much above normal the first part of the week.
Next upper system will move into the region on Wednesday.  It will approach from the west, allowing more time for moisture return than the current system.  Models differ regarding the speed and intensity of the upper system.  GFS was wrong last week and believe it is wrong again for Wednesday.  I’m not convinced that such a strong system will move over Oklahoma resulting in marginal moisture return with no QPF.  EC on the other hand develops QPF across the state and even CAPE values @1000 J/kg.  Given moisture return @50F with 850mb 10C, think that a few severe thunderstorms are possible in strongly forced environment.  Again, very much like what happened on Friday.  NAM is in-general agreement with the EC minus the CAPE.  This is seen through the 850mb moisture on the NAM, which is low and a typical bias of the model.
Next story re this system will be potential for snow as cold air surges southward late Wednesday.  GFS again is  dry and seemingly wrong.  EC appears to have a better solution, although the QPF is somewhat low and I really have to guess when estimating precip amounts.  Since these types of systems have a tendency to slow down or do other fun things, I’m not going to assume this is forecast is easy or given.
Another system looks to approach on Christmas Day, we’ll see how that goes.  EC beyond 168 hours tends to do some funky things.
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