AFD from WFO JAN 4am:
LONG TERM...WHAT I HAD FEARED LAST NIGHT IS BECOMING MORE OF A
POSSIBILITY AS THE OUTLYING MODEL...WHICH WAS DEVELOPING SNOW ACROSS
THE AREA...IS NOT THE OUTLIER ANYMORE. THE GFS...IS NOW LEADING THE
WAY AND HAS STRONG SUPPORT FROM THE SREF AND MOST OF ITS ENSEMBLE
MEMBERS AND SOME SUPPORT FROM THE NAM AND EURO. 8 OF 12 ENSEMBLE
MEMBERS GENERATE MEASURABLE SNOW FRI NIGHT ACROSS THE CWA AND SNOW
PROBABILITIES FROM THE SREF ARE RANGING FROM 40-60%. SUCH SUPPORT
HAS TO BE TAKEN SERIOUSLY AND THE RESULT WILL BE SIGNIFICANT CHANGES
FOR THE FRI NIGHT FORECAST WRT POPS AND PRECIP TYPE BECOMING AT
LEAST LIGHT SNOW.
ONE MAY BE ASKING...WHAT HAS CHANGED TO NOW INCLUDE THIS INTO THE
FORECAST? MAINLY DEEPER MOISTURE AND STRONGER SUPPORT FROM MORE
MODELS. FORECAST LEADING INTO FRI/FRI NIGHT HAS GENERALLY ALWAYS
PORTRAYED SOME SORT OF S/W MOVING THROUGH THE BASE OF THE LONG WAY
TROUGH. HOWEVER...THE TREND LAST NIGHT WAS FOR THE S/W TO BE
STRONGER. WITH THAT...THE LARGE MAJORITY OF THE MODEL GUID WAS
GENERALLY DRY AND ONLY HAD CLOUDS WITH THAT TROUGH PASSAGE. THE GFS
WAS REALLY THE ONLY MODEL SHOWING SNOW ALONG WITH A COUPLE OF ITS
ENSEMBLE MEMBERS. SINCE LAST NIGHT...MUCH MORE SUPPORT HAS COME IN
FROM VARIOUS GUID AND BASICALLY THERE HAS BEEN A 180 SWITCH AND NOT
THE OUTLYING SOLUTION IS THE DRIER VERSION.
AS FOR SOME OF THE DETAILS...THE S/W IN QUESTION WILL BE RATHER
POTENT AND PROVIDE STRONG ASCENT ACROSS THE REGION ALONG WITH
HELPING TO DEVELOP A SFC LOW ACROSS THE N GULF. IT WILL BE THIS SFC
LOW DEVELOPMENT THAT WILL GIVE THE S/W THE MOISTURE TAP TO DEVELOP
PRECIP ABOVE THE COLD AIRMASS. I WILL SAY...THAT UNCERTAINTY IS
STILL FAIRLY HIGH IN THIS SOLUTION AS IT IS SOME 60-72 HRS OUT AND
ANYTIME WE ARE DEALING WITH WINTRY PRECIP IN OUR AREA...THINGS OFTEN
CHANGE. THE GENERAL SETUP FOR THIS WINTRY POTENTIAL FRI NIGHT IS
QUITE FAVORABLE AS WE WILL SEE CAA ONGOING FRI INTO FRI NIGHT WITH
SFC PRESSURES RISING AS HIGH PRESSURE BUILDS IN FROM THE N. THE
COMBINATION OF THE DEVELOPING GULF LOW IS ALSO SUPPORTIVE B/C IT
PROVIDES MOISTURE. THE FLY IN THE OINTMENT IS WILL THE COLDER AIR
MOVING SOUTHWARD BE TOO DRY AND EVAPORATE ALL OF THE FALLING PRECIP.
THAT TYPICALLY HAPPENS. ADDITIONALLY...THE AIRMASS THAT WILL BE IN
PLACE WILL NOT BE VERY COLD AND HIGH TEMPS FRI SHOULD BE IN THE
MID/UPPER 40S. IF CLOUD COVER THICKENS FASTER AND VIRGA DEVELOPS
EARLIER THE EVAP COOLING PROCESS WILL KEEP TEMPS COOLER AND MORE
NEAR 40 DEGREES. WITH FREEZING CONDITIONS NOT ALREADY IN PLACE...WE
WILL NEED OTHER MEANS TO GENERATE SNOW. THAT DOES NOT LOOK TO BE A
PROBLEM AS DYNAMIC COOLING FROM THE STRONG S/W WILL PROVIDE THAT AS
STRONG ASCENT WILL GENERATE PRECIP ALOFT WHICH WILL EVAPORATE AND
COOL ANY LAYER THAT IS ABOVE FREEZING. ALSO...THIS ALL LOOKS TO COME
TOGETHER FRI NIGHT AND WILL BE AIDED BY DIURNAL COOLING WHICH WILL
MAKE IT EASIER TO DROP TEMPS TO CRITICAL LEVELS FOR PRECIP TO BECOME
LIGHT SNOW. IT APPEARS AS MOISTURE VALUES...VERTICAL MOTION AND
DURATION WILL ONLY SUPPORT LIGHT ACCUMULATIONS FROM 1/4 INCH TO
POSSIBLY 1 INCH. THIS WILL ALSO OCCUR WITH TEMPS 31-34
DEGREES...SIMILAR TO PREV SNOW EVENTS OVER THE PAST TWO WINTER
SEASONS.
Forecast:A slight chance of rain before 9pm, then a chance of rain and snow between 9pm and midnight, then snow likely after midnight. Cloudy, with a low around 32. North wind between 5 and 10 mph. Chance of precipitation is 70%
w00T!
