Winter Storm

Here we go!

When winter weather is in the forecast, it's funny watching the
meteorologists and weather enthusiasts when the new models come out.
It makes the oldest person become a kid again, everyone is very
anxious and gets excited (or depressed) as soon as they hear the
results. I know you must remember the feeling as a kid on the night
before Christmas, this is the adult version of that.

The models are still good to us this morning, and we apparently have
their blessing. Here's where we stand right now.
We are colder this morning than forecasted, not just at my weather
station, but about 4 degrees colder across a very wide area. If we can
carry this trend through the day we will be in good shape. At the time
of this writing, it's 14.7 degrees, so we now have a frozen surface
for precipitation to fall on unlike the Christmas snowfall.

I still believe the precipitation will begin around the midnight time
frame and continue through the day tomorrow and probably into Tuesday.
The trailing end of the precipitation will be freezing rain and at
this point that looks like a given. We could see up to .25" of
freezing rain on top of the snow and this will be very important to
watch. What will happen after the majority of the snow falls, is that
the very cold lower level of the atmosphere is shallow and has warm
air over running the top of it. That warm level will get lower and
lower which doesn't give the warm precipitation much cold air to fall
though. So it falls into the shallow layer of below freezing air where
it freezes on contact. This will make a glaze of ice on top of the
already heavy snowfall. The big concern is how much freezing rain/
drizzle will fall. Even .25" of ice is extremely dangerous and I do
expect to see power outages in the metro area. Of particular concern
are those areas south of Atlanta, this will be a devastating ice
storm, not just in Georgia but over the entire southeast.

We will begin as snow and should remain all snow until the end when we
transition to freezing rain. I haven't made any predictions until this
point and still very reluctant to do so due to the number of unknown
variables still out there, but based on the trends, I would say we're
looking at a 7"+ snowfall in Gwinnett. I wouldn't expect it to be much
lower on the low end but could go to 10"+ in isolated areas if a
strong band happens to cross our area. It's possible a deformation
zone could setup as the moisture is lifted rapidly by multiple methods
over the cold air. Isentropic lift, the normal rise due to the
mountains to the north, and forcing by upper level winds all can help
to fuel this intense band of snow, and in this zone snow can
accumulate rapidly. Something to watch for.

Another thing that can affect the amount of moisture we receive...
enhanced convection in the Gulf of Mexico can sometimes cut off the
moisture transport to our area which would greatly reduce the amount
of snow we receive. I believe that the convection will decrease before
that will become an issue but this is also something else to be
watched today.

I'm providing some links that I think will be informative today,
1. Deep South Google NEXRAD Radar - This radar loop covers the entire
southeast US and loads 36 actual NWS radar sites. It's a little slow
to load so please be patient. Once you get it loaded, you can just let
it run all day, it updates and refreshes automatically.
http://www.daculaweather.com/ridge_southeast_wide_master.php

2. GRLevel3 Atlanta NEXRAD - This radar loop runs from custom software
that takes higher level data from the National Weather Service to give
you a more detailed image and considerably more information that a
regular loop. From this you can see temperatures, wind, and reported
precip. I have 5 of these running today, Jackson MS, Birmingham AL,
Robins AFB GA, Greenville SC, as well as the Atlanta loop. Please
visit my website for all of the links and other radar products.
This is Atlanta - http://www.daculaweather.com/grlevel3/ffc_284.php

3. I also have a nice Weather Underground interactive Wunder Map
http://www.daculaweather.com/wu_wunder_map_new.php

I will keep you updated throughout the day as things develop, at this
point the we can almost throw the models out the window and rely on
observations and radar to determine the actual course of events. This
will be very interesting to watch as it evolves today, just know
you're about to experience a once in a quarter of a century weather
event!