Wednesday, November 23, 2011

Update on Holiday Weather...Including Big Weekend Storm...

The outlook that I posted on Saturday valid for today and Thanksgiving Day is still on track. A cold front is currently pushing rain and some Northern snow out along the Eastern seaboard this morning, and most areas will be cleared of precipitation by Noon or shortly after.

Thanksgiving Day will be quiet across all but the far western part of the country, where valley rain and mountain snow showers will be on the increase during the day as upper level energy increases across the region.

The next big event will be the weekend cold surge and associated storm system, which I first talked about yesterday.  

As I mentioned yesterday, there was considerable division among the computer forecast models, but they are gradually moving toward more of a consensus solution during the last few runs.  

Below are the GFS model images valid at 6pm CST on each of Friday, Saturday, Sunday and Monday.  The left half of each image is the model's forecast of conditions near the middle levels of the atmosphere, while the right half of the image is the model's forecast of surface conditions.  I have drawn the surface cold front in blue and circled the middle/upper level storm system in yellow on the respective portion of each image:

In a nutshell, this is still shaping up to be a very interesting / active situation for the upcoming post-Thanksgiving weekend.  As you can see, a surge of cold air is forecast to rapidly advance Southward into the central and southern Plains on Saturday.  As upper-level energy approaches from the West and Southwest, precipitation will break out along and either side of the cold front.

The near surface airmass is forecast to become cold enough for wintry precipitation, as noted by the dashed red lines immediately behind the cold front.  This current model solution suggests that the upper level storm will slow way down and/or become nearly stationary over the lower Mississippi Valley region by late Sunday and into Monday.  This could enhance the potential for snow and/or a wintry mix of precipitation across portions of Arkansas, Louisiana and Mississippi by late in the weekend and early next week.  This threat would then progress Eastward across the Deep South as the system moves slowly East into the middle of the week.

Below is the current GFS model forecast of the snow depth across this region valid 6pm CST Monday, November 28th (area being discussed circled in purple):

Keep in mind, the above image shows the actual depth of snow that is forecast to be on the ground at that time (currently forecast at 1-2 inches).  More snow will have fallen prior to this time and melted before the ground became cool enough for accumulation.  The model also has a harder than normal time forecasting snowfall in this type of situation.  We should take the current 1-2 inch forecast lightly (literally) until it becomes more clear how this is going to unfold.  What I mean to say is that given the right conditions, we could potentially be dealing with considerably more snow than the model is currently estimating.

The other important take away on this is that as things currently stand, if the above solutions come to fruition, this will be a Southern storm as far as the snowfall potential goes - not a Midwest storm.

I'll post more detailed updates as this situation continues to unfold.  I am currently away from home base so I can't draw maps, etc., to really illustrate the outlook as I would like to.  I plan to make an updated post with easier to understand mapping of the event later today...

Bottom line, if you live and/or have travel plans across this region for this weekend or into early next week, you definitely want to keep abreast of the latest updates on this developing weather situation...

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Anthill_Goddess said...

Glad to see the models starting to come to a little bit of agreement (there's a joke about congress in there...but I'm not going there! *heh). Am I wrong in thinking that it's much less uncommon for Arkansas, etc. to have a snow storm than it is for us in the upper midwest to see them? I don't normally worry too much about winter weather outside of my own area so I'm not sure!

Rob In Texas said...


It's pretty unusual for this type of system in the Deep South this early in the season. Accumulating snow in January or February wouldn't really be too unusual, but it would be for late November...

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