Monday, February 7, 2011

Much anticipated first call for Wednesday's snow from MWN

Somehow today's snowfall caught many folks seemingly by surprise, despite the good coverage and forecasting of it by weather folks across the area. While totals north of the metro were likely higher than most of us anticipated (northwest TN received anywhere from 3-6"+), widespread 1-2" amounts within the Memphis area were pretty much dead on with forecasts and the timing forecast was great as well.  Rain changed to snow in the 7-9am timeframe, depending on the side of the city that you call home and accumulating snow was about done by 11am, though light snow showers and flurries continued into the early afternoon.

I believe the reason people were caught off-guard by today's snow is the same reason coaches don't want their sports teams looking past the next game - they might overlook a seemingly less worthy opponent and get caught flat-footed. In this case, there's been so much talk about the Wednesday snow (for nearly a week now) that the Monday storm got overlooked. Now that today's event is done, let's go ahead and start talking about it's more-hyped big brother. First the knowns:

1) Weak low pressure at the surface and aloft will move out of Texas and along the Gulf coast and will generally be weakening as it does.
2) The airmass leading into this system is colder than today's was, thus we will have an all-snow event. There will be no transition from rain and no ice expected.
3) Accumulation is pretty much a given (the amount is not) and the snow will be somewhat drier than today's wet good-packing snow and will not be quite as good for snowmen!
4) Someplace in Arkansas, probably in the west-central portion of the state, is going to get dumped on.  I wouldn't be surprised to see a foot of snow somewhere over there. Closer to home, snow will likely be deeper as you go SOUTH, into northwest MS, than north into west TN.
5) Timing seems to be fairly similar among all models with the accumulating snow expected from mid-afternoon Wednesday through midnight or shortly after - roughly 9 hours of snow.
6) A Winter Storm Watch has been posted for much of AR, west TN, and northwest MS for Wednesday.

What is not a given, and would answer everybody's question - "How much?" - is this: computer models are generally falling into one of two trains of thought regarding the strength of the low and snowfall amounts. These two "camps" have been bullheaded about staying in their respective camps for some time and farther apart than I would like as we get within 48 hours of the event commencing.

One train of thought, which is led by the well-known and respected GFS model, shows a very weak system passing well to our south and bringing only an inch or snow of snow.  One of the better mid-range models, the European (or ECMWF), also shows a pretty weak system as of the past couple of days, but seems to be bringing a little more snow than the GFS, even given it's lack of punch.  (It should be noted that last week the GFS showed accumulations of a foot or more before it flip-flopped back to the low end of the spectrum.)

The second train of thought followed by the well-known NAM (which has seemed to overestimate snow amounts the past few times) and other higher-resolution models, as well as the mid-range Canadian GEM, is stronger with the upper-level low, and thus dumps more precipitation on the region. The range from these models seems to be 3-5".

So, given all of this, my initial estimate for the metro area is 2-4", beginning after 2pm Wednesday and ending around midnight (12:00am Thursday). Higher amounts in that range will generally be over northwest MS, while lower amounts would be north of the big city. I'll update as conditions warrant and certainly will be covering this storm on Facebook and Twitter just as with the others in this endless string of winter!

As a side note: a rapid and noticeable warming trend appears to be taking shape heading into the weekend. It appears as though it may be a fairly long-lasting one as well!  Perhaps this will be the last Mid-South snowstorm of the winter... we'll see!

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