Monday, November 28, 2011

Southern Snow Event Still Setting Up for Tonight, then Northward on Tuesday...

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***Updated at 12:25 PM CST:
The latest GFS computer forecast model runs are in and there is no significant change to the idea of locally "heavier" snowfall amounts along the Mississippi / Alabama / Tennessee border areas tonight:

You can see that the computer model has edged the 1-2 inch accumulation band back Westward to now include the greater Memphis area.

I may not have made myself clear on this idea in my original post, but I would suggest that you pay more attention to the area in which the accumulating snow is being forecast by the model vs. the actual amount that is being forecast by the model at this time.

Based on what we're seeing right now, I would generally expect to see 1-3 inches of snow within (or near) the darker pink shaded area on the above image, and possibly as many as 2-4 inches within (or near) the light blue shaded area on the same image.  

I'll have a more detailed update under a new thread later today...

-------------------------------Original Post:

Right before Thanksgiving I made a post stating that snow would be a possibility across the Deep South and the Mississippi Valley region early this week.  The latest computer model runs continue to support this forecast, and we are now able to be more specific as to the location and magnitude of the event as well.

Its important to keep in mind that all things are relative.  What may not be a big deal to New York City (snowfall wise) can be quite a big deal indeed to folks in the Deep South, where just an inch of snow can seemingly bring commerce to a near halt in some areas.

Below are the latest GFS computer model forecasts of snow depth valid at 6am CST on Tuesday and 6am CST on Wednesday:

I underlined the words "snow depth" in the last paragraph to illustrate a point.  The ground across the Deep South and mid-Mississippi Valley region is warm, which will have a significant impact on the accumulation of snow.  In some areas, snow will fall at a rate that would normally accumulate very rapidly given cold ground conditions, but in this case, much of the snow will melt before beginning to accumulate.  This is obviously good news for those who have to drive across this region tonight and Tuesday, but is bad news for you snow fans out there.

Despite the relatively warm ground conditions, it appears that snow will be able to accumulate across portions of the region tonight and early Tuesday.  Lets take a closer look at the GFS model snow depth forecast centered on the Memphis area on the image below:

Most of the snow in areas on the above image would fall during the overnight hours tonight and early Tuesday morning.  As you can see, the model is forecasting a fairly widespread swath of 2-3 inch snows immediately East of Memphis, with a small 3-4 inch bullseye to the Northeast of town.  This will be surrounded by a larger area of 1-2 inches of snow covering Northern portions of Mississippi and Alabama and into western Tennessee.

By Tuesday afternoon and evening, snows are forecast to spread North/Northeastward into portions of Kentucky, Indiana and Illinois, then reaching Michigan by late evening and into Tuesday night (please refer back to  the 2nd image from the top of the post).  Due to colder ground temperatures and heavier snowfall rates in this region, some significant accumulations are likely across portions of Michigan and northern Indiana, as indicated by the latest GFS forecast below, which is zoomed-in on the Michigan/Indiana border region:

As you can see, the model is forecasting as much as a foot of snow across portions of southwest Michigan by Wednesday morning.  I am confident that widespread snows of 6-8 inches are likely in this region, with localized amounts near 10 inches.  The model may turn out to be correct in forecasting amounts near one foot, but I think that will be on the more extreme end of the scale based on what we're seeing right now.

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