FCST: 12/23-25/2009 Winter Wx Event--Central Plains / Svr Storms Gulf Coast States

5 Day surface map forecast--Issued 1843Z/19

EDIT (17Z/20): Several of the computer models are forecasting a more northerly track for this storm system, which would put the heaviest snows across IA, southern MN and into WI.  The ECMWF has been trending this way for a couple of runs now and the GEM and GFS went this way last night.  I still want to see some model consistency from run to run on all of the operational models.  Right now the low tracks through SE KS through Central MO and into SE IA by Thursday morning.  The heaviest snows will fall and north and west of the track of the low.  This is why forecasting winter storms this far out is not wise and not more than a guess based on what one computer model thinks is going to happen.  The data used is only as good as the data entered.  However, one thing to keep in mind is the jet stream is stronger and further south in the winter, so this could impact how far north the track of the ULL will be.  I will be looking at the 18Z data shortly for consistency from run to run.  This may not occur until the storm system comes onto the west coast and we get some good sampling data! 

Forecast thoughts ATTM: I am still thinking precip breaks out late Tuesday into Wednesday and beings as light freezing rain and/or freezing  drizzle (all depening on the thermal profile of the column).  During the day Wednesday I look for the precip to transition to all rain as warm air is advected north.  I do not expect the rain to transition to snow until Wednesday night as cold air is pulled into the system as the system moves by to the north and east.

Some parts of the Upper Mississippi Valley are going to see a lot of snow.  I am watching the 850mb temp line very close as there is a very slim chance this could be a freezing rain event for us, at least during the early periods. 

SWODY4

Severe weather remains a possibility over the Gulf Coast States.  I anticipate severe weather from E. TX to LA to MS during this event.  SPC has it marked for the Day 4 period. ~ CS

Old Discussion

A major winter storm is taking shape, per forecast models, to affect the central plains beginning as early as Tuesday night and lasting through Thursday.  My current thinking is this storm will start off as light rain/snow mix Tuesday night and transition to all snow by Wednesday with a possible long duration snow event for someone in the central plains.  The 12Z/19 GFS paints the heaviest snow totals over Northern MO and Southern IA, however, the models have been very inconsistent and I am not willing to bite the forecasted track just yet.

It is way to early to talk accumulations but someone within 200 miles of our local area is going to have a white Christmas, VERY NICE!  Pay attention to local NWS forecasts as this storm is going to hit during the big holiday travel period.

In addition a severe weather outbreak is possible across east TX, LA and MS during the same time period.  December (winter) severe weather outbreaks are more danagerous than spring as people are more complacent and think severe thunderstorms are not possible!  If you have friends and family in the above described areas please ask them to pay attention to NWS forecasts and local commercial media outlets as this storm system unfolds next week!

In the meantime, I am going to be looking at this more closely this weekend and will post more info by Sunday night!  Have a great weekend!  ~ CS