Heavy Snow threat 2/9/11-2/10/11 AR AL MS TN

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Quote: James Spann | 1:04 pm February 5, 2011 | Comments (2)
Yet another challenging week ahead for Alabama meteorologists. Everybody is looking for answers that quite frankly can’t be handled very well more than 48 hours in advance. I am getting email and Facebook and Twitter messages from people telling me that various people are forecasting a “historic” snow for Alabama this week, and they want to know what I think.
Long time blog readers know my usual response… I honestly don’t care about what anybody else says, I simply don’t have the time or interest. All we do here is tell you what we think will happen with full explanation and openness.
This is where we are right now…
MONDAY: The first wave of the week will bring some light rain to the state Monday, with some risk of a little light snow on the back side of the departing system Monday evening. Here is the RPM output below for 4:00 p.m. CST Monday… showing the most widespread snow over the northern quarter of the state, and it is very light…

There could be a dusting of snow for that part of Alabama Monday evening, but precipitation should be pretty light.
WEDNESDAY/THURSDAY: If we are going to get a big winter storm, this is the time. Again, there is not much skill in forecasting snow placement and amounts more than 48 hours in advance around here. Why some people choose to do it is a little baffling.
The GFS has been advertising a big North Alabama snow for a number of runs, but it has backed off in recent runs. Below is a look at the forecast snow for Birmingham from the GFS using BUFKIT data:

The last few GFS runs, as you can see, are now printing only a dusting to 1.2 inches for Birmingham. Runs from yesterday were in the 6 to 10 inch range.
The ECMWF, which has performed pretty well this season, is now more aggressive. Below is the output valid Thursday morning at 6:00 a.m. CST…

That would suggest a very good snow for the northern third of Alabama.
BIG TIME COLD: Aside from the snow, some very cold air will come in here late in the week… you can see the GFS in recent runs is suggest mid-teens by Friday morning… the runs were colder yesterday with 0 degrees (F) showing up…

BOTTOM LINE: There is a chance of some significant snow for parts of Alabama (most likely the northern counties) Wednesday night into Thursday morning, but it is way too early to be specific on amounts or placement. And, it will turn much, much colder at the end of the week, perhaps the coldest air so far this season.
All of the armchair meteorologists will probably make wild forecasts of big snow, and who knows, they might right, but NOBODY right now knows. I recommend this weekend you spend some time with your family, take a long walk, get a little fresh air, and relax. The 48 hour rule means the first snow accumulation potential graphic won’t show up here until Monday night, most likely.
Enjoy the weekend!!!!

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Quote:
Late Night Forecast Thoughts…

Bill Murray | 12:16 am February 6, 2011 | Comments (11)
Everyone wants to know if we are going to have a monster snow Wednesday and Thursday. That idea has been on the table since it was a feature of a few GFS and European model runs this week. While the models have backed off from this solution over the past several runs, this has been the winter of the unexpected. We will actually deal with a minor winter threat tomorrow night with the main even coming Wednesday night and Thursday followed by some cold conditions for late in the week and the weekend. How cold? How much snow? Let’s see what we can tell…
TONIGHT/MONDAY: Clouds will thicken this evening and a few showers may arrive by midnight. Dewpoints are in the upper 20s already, so cooling by evaporation will not be a problem tonight. Temperatures will drop into the lower 40s before skies cloud over, and this should keep the precipitation liquid through much of the overnight hours. The approaching disturbance will cool the mid levels of the atmosphere, setting the stage for the precipitation to mix with or briefly change over to snow by late in the day Monday. In any case, temperatures will be in the lower and middle 40s on Monday, preventing any accumulation issues. A brisk westerly wind will kick in by afternoon. As skies start to clear Monday night, lows will fall back into the upper 20s.
WEDNESDAY NIGHT
Precipitation is expected to begin before midnight across North and Central Alabama Wednesday night. It looks like it will be snow over the north, with a rain/snow mix over Central Alabama. Rain will likely change to or be all snow all the way down to the I-20 corridor Wednesday night. Lows will drop to near freezing in the I-20 corridor, with colder readings to the north and warmer conditions to the south. Thursday will feature colder conditions

ACCUMULATIONS: It’s still too early to try to be specific about snow accumulations for Wednesday night and Thursday. Recent model runs have not shown the signs of a huge accumulating snow, with the best moisture south of the colder temperature profiles. But the idea of there being a few hours of light snow in areas north of I-20 is a good possibility. This is what the accumulated snow chart looks like from the evening GFS run. This looks like a very plausible solution to me.
TURN TO COLDER: Thursday will feature colder conditions with a brisk northwesterly wind and temperatures rising only a few degrees at best into the middle 30s. Indeed, temperatures may remain steady during the morning hours before falling by afternoon. Lows will be in the teens by Friday morning, and should remain in the 30s during the day. Saturday will be slightly warmer. Sunday looks a lot like Saturday.

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Quote:NAM Cold, Wet (Snowy) for Wednesday Night

Bill Murray | 9:11 pm February 6, 2011 | Comments (7)
The evening run of the NAM is coming in wet and cold for Wednesday night, giving more confidence to a snowy forecast for late Wednesday night for Central Alabama.
Here is the precipitation and 850 mb 0C isotherm for midnight Wednesday night. It shows snow spreading into areas north of US-82 and I-20. The 850 mb temp is the temperature at 5,000 feet. It is a good rule of thumb for the rain/snow line. If the NAM verifies, we could see a general 2 to 4 inch snowfall across North Central Alabama Wednesday night.
We are still dealing in speculation based on model data at this point. We will start to deal in specific forecasts by tomorrow night.

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Nashville

Quote:ON WEDNESDAY...DEVELOPING SFC/LL LOW WILL MOVE INTO THE WESTERN GULF
AND CONTINUE EASTWARD TRACK WEDNESDAY NIGHT. DEEPER MOISTURE WILL BEGIN
SPREADING INTO THE AREA DURING THE DAY...WITH SNOW AND/OR MIXED
PCPN BREAKING OUT IN THE AFTERNOON. WEDNESDAY NIGHT...BRUNT OF SNOWFALL
EXPECTED...WITH SEVERAL INCHES STILL POSSIBLE ALTHOUGH GFS CONTINUES
TO BACK OFF OF BIG EARLIER AMOUNTS PUSHING GULF LOW FURTHER AND FURTHER
SOUTH.

LONG TERM...
ISO-SCT LIGHT SNOW SHOWERS WILL LINGER WELL INTO THURSDAY...ENDING
LATE AFTERNOON EAST. LITTLE ADDITIONAL ACCUMULATION EXPECTED THURSDAY
ALTHOUGH MAYBE THE PLATEAU PICKS UP ANOTHER HALF TO INCH OR SO.

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[Joe-Nathan]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAKE CHARLES LA
616 AM CST MON FEB 7 2011

Quote:...COLDER AIR SPILLING INTO THE REGION BEHIND THE FRONT LOOKS TO
OVERLAP WITH ENOUGH RESIDUAL MOISTURE TO PROVIDE AT LEAST A CHANCE
OF WINTER PCPN OVER PARTS OF THE AREA PER PARTIAL THICKNESS
METHOD. A DEEPER EXAMINATION VIA MODEL TIME HEIGHTS/SOUNDINGS
AND THE TOP DOWN METHOD INDICATE A COLD RAIN GIVEN THE LACK OF ICE
INTRODUCTION ALOFT. FORECAST SURFACE TEMPERATURES OVER THE EAST
TEXAS LAKES REGION INTO CENTRAL LOUISIANA ARGUE FOR A CHANCE OF
FREEZING RAIN/DRIZZLE BEFORE LIFT COMES TO AN END THURSDAY
MORNING. PREVIOUS FORECAST HAD A SLIGHT CHANCE/CHANCE OF RAIN OR
FREEZING RAIN MENTIONED...AND THIS STILL LOOKS REASONABLE. NO
SIGNIFICANT ACCUMULATIONS ARE EXPECTED...

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Jackson MS

Quote:WEDNESDAY THROUGH NEXT SUNDAY...

BY FAR THE PRIMARY CONCERN LATER IN THE WEEK WILL BE THE POTENTIAL
FOR ACCUMULATING SNOWFALL FROM LATE WEDNESDAY INTO EARLY THURSDAY.
CONFIDENCE IS INCREASING THAT NORTHWEST PORTIONS OF THE
ARKLAMISS...ESPECIALLY OVER THE UPPER DELTA REGION...COULD RECEIVE
AROUND 2 TO 4 INCHES OF SNOWFALL...WITH LIGHTER AMOUNTS POSSIBLE AS
YOU GO FARTHER SOUTHEAST.

MODELS...ESPECIALLY THE GFS...HAVE TRENDED DRIER OVER THE PAST
COUPLE OF DAYS DUE TO THEIR QUICKER DAMPENING OF THE SHORTWAVE TROUGH
RESPONSIBLE FOR THIS POTENTIAL SNOW EVENT. BASED ON RECENT
SIGNIFICANT TROUGH PASSAGES...BELIEVE THERE WILL BE LESS PHASING OF
THE STREAMS THAN INDICATED BY THE GFS...THUS RESULTING IN A MORE
DISTINCT TROUGH PASSAGE AND MORE PERSISTENT WARM ADVECTION AND LARGE
SCALE ASCENT - SO HAVE RAISED MAV MOS GUIDANCE POPS AND GFS QPF
CONSIDERABLY AS A RESULT FOR WED-WED NIGHT.

PRECIPITATION TYPE WILL BE EITHER RAIN OR SNOW WITH THIS SYSTEM AS
DEEP COLD AIR MOVES INTO THE ARKLAMISS AT THE SAME TIME THAT SURFACE
LOW PRESSURE DEVELOPS OVER THE NORTH CENTRAL GULF. IN GENERATING THE
FORECAST GRIDS FOR SNOW VS RAIN...HAVE FOLLOWED A BLEND OF THE
ECMWF/SREF AND THEIR CONSENSUS 1200 FT AGL WET BULB ZERO HEIGHT
LOCATION. IT IS POSSIBLE THAT PRECIPITATION WILL BEGIN AS SNOW OVER
UPPER THE DELTA REGION WEDNESDAY AFTERNOON...BUT GENERALLY EXPECT
PCPN TO BEGIN AS RAIN BEFORE EVAPORATIVE COOLING/MELTING ALOFT CAN
LEAD TO A CHANGE-OVER TO SNOW AS THE BOUNDARY LAYER COOLS. THE
BEST FRONTOGENETICAL FORCING AND COLDEST AIRMASS WILL COINCIDE OVER
THE UPPER DELTA REGION AND THIS IS WHERE THE HEAVIEST SNOW
ACCUMULATION IS ANTICIPATED. ELSEWHERE...WEAKER MOISTURE TRANSPORT
AND LESS EFFICIENT SNOW PRODUCTION WILL LEAD TO LIGHTER AMOUNTS.

THERE IS STILL MUCH THAT COULD CHANGE REGARDING POTENTIAL SNOWFALL
AMOUNTS SHOULD THE TROUGH MAINTAIN MORE/LESS INTEGRITY THAN THE
MODELS SUGGEST. FOR NOW WILL RAMP UP THE WORDING IN THE HWO TO
REFLECT HIGHER CONFIDENCE IN ACCUMULATING SNOWFALL...PARTICULARLY
OVER THE UPPER DELTA REGION.

THURSDAY AND BEYOND...THE LOW PRESSURE SYSTEM WILL BE QUICK-HITTING
AND PRECIPITATION WILL WIND DOWN QUICKLY THURSDAY MORNING WITH A
STRONG COLD ADVECTION PATTERN TO FOLLOW. VERY CHILLY CONDITIONS WILL
PERSIST THROUGH FRIDAY...BUT A SIGNIFICANT WARM-UP IS STILL ON TAP
FOR THE WEEKEND AS ZONAL FLOW SETS UP AND BRINGS MILD PACIFIC AIR
INTO THE REGION. /EC/

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