FCST: 12/23-25/09 Winter Wx Event--Central Plains

HPC Surface Forecast 12Z December 24, 2009
(Places ULL in SW MO)

HPC Surface Forecast 12Z December 25, 2009

(Places ULL in SE IA)

EDIT 6Z/21: Latest data rolled in earlier this evening and the models are still not coming into "total" agreement. GFS has moved a bit further south than the previous run (back toward earlier runs), while the ECMWF, UKMET and GEM are still farther north and west with their tracks (somewhat consistent). 

Some of the models are slowing the system down and letting it dig in the desert southwest before it kicks out into the plains, making this a late Wednesday night through Christmas event.  A lot of inconsistencies, as has been the case the last few days, to try to pin down a track this early.  You also need to keep in mind this storm system is just entering the sampling network in the Pacific Northwest.

EMCWF Model Forecast valid 12Z December 24, 2009
(Places the ULL in SE KS)

GFS Model Forecast valid 12Z December 24, 2009
(Places the ULL in SE KS / NE OK)

GEM Model Forecast Valid 12Z December 24, 2009
(Places the ULL in SW IA)

Here is a look at some of the past 24 hour GFS run storm track outputs. Pay attention to the storm tracks from the south/southwest (Oklahoma and Arkansas area) as this is our storm:

Once we get some get sampling data on the storm and get closer to the event it is going to be a "little" easier to pin down the track of the upper level low. A secondary low is also showing up on some model runs and trying to phase with the main system as it ejects northeast of the local area. This may leave some lingering snow showers into Saturday. Way to early to talk accumulations and if you see any forecasts it is a "best guess" or wishcasting scenario at best. A freezing rain event is in the back of my mind as well, but not the classical set up for a crippling ice storm due to no cold air at the surface. If we do get ice, it will be light in nature and more of a nuisance to travel than anything. Albeit, it is occurring during the Christmas holiday travel period.

Winter forecasting is always difficult and highly dependent on the track of the upper level low. Now factor a few variable surface parameters into the equation and WOW!  We have no artic or even cold air for that matter in place.  Add in the warm air advection (WAA) with the moisture transport from the Gulf of Mexico and it really muddies things up.

 The 1000-500mb thickness (540dam), 850mb 0C and Warmest Vertical Temp 0C lines remains north and west of the Cameron (4-county area) for most of this event. If this were to hold true, any frozen precip that falls will be well north and west of the local area leaving us with all liquid precipitation.  The overnight hours would be the only concern for me right now for freezing drizzle / freezing rain as the surface temps drop below freezing and the 850mb temps remain above freezing.

Here is a basic ULL track for us to get heavy snow:  The ULL would need to roughly track near Fort Smith, AR and turn north/northeast and track between Columbia and St. Louis, MO. The more time it takes the ULL to follow this track the more prolonged our snow event will be and the more accumulation we would receive. In addition, the atmospheric column and surface/near surface temps have to be cold enough to support snow.

A lot of stuff to think about and digest for sure!!  More tomorrow after I have the chance to look at some more data and get a chance to look at some surface parameters as the storm is moving inland! ~ CS