Feb 17, 2012; 10:30 AM ET
Friday, 11:15 A.M.
If I didn't know better, I think I would call this more of an early-spring storm, rather than a winter storm. Why? For the simple fact there will rain, snow, and severe weather all wrapped into this storm that will get more impressive with time. In most winter storms, you tend not to get much, if any, severe weather, just the snow (and ice) on one side of it, and rain elsewhere. Throw in the fact it will be very mild in the East and Southeast ahead of the storm, and not terribly cold behind it, especially west of the Appalachians, and it seems more suited to a 'spring' storm. But I won't fret over what you or I wish to call it. It will rain, it will snow, and there will be some severe weather.
Here's the big picture view from a pretty picture:
That simplifies things quite a bit, almost too much, in fact! It leaves
out one of the key factors with regard to the path of the storm, and
that's the lead disturbance that will streak across the Upper Midwest
into the northern and eastern Great Lakes later tonight and tomorrow
morning, then drive a weak but very definable cold front to the
Northeast coast tomorrow night. The GFS ensembles are another tool that
really help to show this separation nicely tomorrow morning between this
feature and the storm lagging behind near the Texas Coast:
The model consensus is much tighter today, and while there will still
be some minor changes in the overall storm track and timing, things
look pretty much on target for a track originating along the Upper Texas
Coast and adjacent Northwest Gulf of Mexico waters late tonight and
tomorrow morning, then cutting east-northeastward through northern
Georgia late tomorrow night, and then off the Outer Banks/northeast
North Carolina Coast by early Sunday night.
Aside from limiting the phasing potential of this southern stream
storm and thereby limiting the northward advance of the cloud and
precipitation shield, the other impact of the northern stream
disturbance is to bring cold air to the sidelines ahead of the storm
Saturday night. As the storm deepens Sunday and tracks across the
Carolinas, a northerly wind will drain this colder air southward into
the storms' circulation. In time, this will steadily cool the boundary
layer (finally!) to the point at which falling snowflakes will not melt
before reaching the ground. At this changeover point, it then becomes a
matter of precipitation rates, and the length of time it can snow. Those
two factors will then determine how much snow falls in any given area.
And given the fact it is going to behave more like a spring storm,
rather than a mid-winter storm, there may be some wild fluctuations in
snow fall totals over relatively small distances as banding features
develop. Furthermore, elevation will be another factor in assessing
final snow fall tallies, which is why our initial thinking is that areas
of western Virginia into West Virginia, northeast Tennessee, and
eastern Kentucky will probably have the snow fall totals from this storm
when it all shuts off Sunday night. Many areas here could easily exceed
six inches of snow, and some may eclipse a foot.
As has been my thinking all week long, it will snow in the big cities
like Washington, D.C., Baltimore, and Philadelphia, though after it
starts as rain. But you'll want to be west of these cities to get
healthy snow totals, with the greatest amounts west and northwest of the
nations' capital.
South of these areas, where its mostly or all rain, there will be a
lot of it, and flooding is a real concern from central and East Texas
all the way to southern Virginia. While this won't be precise, the NAM
total precipitation forecast through Sunday night is impressive:
The core areas from central Texas across Louisiana all the way to
North Carolina are forecast to pick up two inches or more of rain. No
doubt some will nearly double that, especially with the expected strong
thunderstorms.
And, of course, it being a spring-like storm, there will be severe
weather. It should start to show up late tonight or tomorrow morning
over parts of Southeast Texas and Louisiana, then spread eastward across
the central and eastern Gulf Coast states later tomorrow and tomorrow
night before ending Sunday morning.
There should be some interesting temperature variations behind this
storm Monday and Tuesday. Where the ground is covered by snow, and it
clears out with winds becoming calm Sunday night, probably west of the
Appalachians, there will be some true pits of cold, with temperatures
ending up several degrees most numerical guidance, and noticeably lower
than surrounding areas without the snow cover. The same is true in and
east of the Appalachians Monday night, especially as high pressure
builds overhead. The nights are still more than 11 hours long, and a
fresh snow pack behind a storm with a clear sky and no wind is ideal for
radiational cooling.
This snow will be largely melted by the middle of next week, though,
especially out of the mountains. Look at the GFS forecasted 850mb
temperatures for Tuesday afternoon:
With a decent amount of sunshine and a nice breeze, that should
easily boost temperatures into the 40s and 50s over the snow fields of
the mid-Atlantic and points west, and as the dew points rise at midweek
ahead of the next storm, much of what remains after that should get
steadily eaten up, by day or by night.
Lest one think that after this storm exits, and the snow melts, that
winter is over, no so fast, my friend! After a mild start to next week,
it finally looks to turn colder in Canada, our usual source region of
cold across the country. And the parade of systems across the Pacific
and into the western U.S. shows no signs of ending. In fact, a couple of
different computer forecasts are jumping on a system in the Rockies and
western Plains late next weekend, one that could tap some of that cold
air and develop into an all out blizzard on one side of the storm, while
more severe thunderstorms try to break out on the warm side. Obviously,
that's a long way off, and much can and probably will change to alter
that specific scenario between now and then. Regardless, the pattern
looks to remain very active going forward through the rest of February
and into early March.
On a brighter note, the best phrase I've heard can now be uttered across the land this weekend:
'Pitchers and Catchers Report.'
Spring cannot be far away now! :)
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