Morning NWS AFD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
335 AM EDT SAT MAR 24 2007

...MORE SPRINGTIME ACCUMULATING SNOWFALL EXPECTED TONIGHT...

.SHORT TERM /TODAY THROUGH SUNDAY/...

COMPACT BUT POTENT SHORT WAVE CURRENTLY LOCATED OVER NORTHERN 
MINNESOTA EARLY THIS MORNING WILL QUICKLY MOVE SOUTHEASTWARD TODAY 
AND MOVE ACROSS NEW ENGLAND TONIGHT. THIS SYSTEM WILL BRING ANOTHER 
SPRINGTIME PLOWABLE SNOWFALL TO PORTIONS OF SOUTHERN NEW ENGLAND 
TONIGHT...MAINLY THE HIGHER ELEVATIONS.

TODAY WILL ACTUALLY BE QUITE PLEASANT...WITH MOSTLY SUNNY SKIES AND 
LIGHT WINDS FOR A GOOD PORTION OF THE DAY. THERE WILL BE A 
NOTICEABLE INCREASE IN CLOUDS THIS AFTERNOON...ESPECIALLY OVER 
WESTERN PORTIONS OF THE CWA. TEMPERATURES WILL BE RIGHT AROUND 
NORMAL FOR THIS TIME OF YEAR.

FOR THE SYSTEM TONIGHT...PREFERRED A BLEND OF THE GFS AND NAM FOR 
TIMING AS THE GFS ON ITS OWN SEEMED TOO FAST. IN ANY EVENT...AS THE 
SHORT WAVE APPROACHES...PRECIPITATION WILL BREAK OUT ACROSS SOUTHERN 
NEW ENGLAND FROM WEST TO EAST EARLY THIS EVENING. WENT CAT POPS ALL 
ZONES BY 02Z. HAVE WESTERN ZONES CATEGORICAL BY 00Z. EXPECT THE 
PRECIPITATION TO BEGIN AS A RAIN/SNOW MIX FOR ELEVATIONS ABOVE 
500-750 FEET OR SO...WITH PLAIN RAIN LOWER THAN THAT AS BOUNDARY 
LAYER TEMPS WILL STILL BE QUITE WARM.

WHAT HAPPENS THEREAFTER IS A LITTLE TRICKY AS BIG TIME DYNAMIC 
COOLING IS LIKELY TO OCCUR. THE NAM IS MOST IMPRESSIVE AS FAR AS 
STRENGTH OF DYNAMICS GO...BUT THE GFS ISN'T ALL THAT FAR BEHIND. THE 
NAM PROGS VERY IMPRESSIVE MID LEVEL FRONTOGENETICAL FORCING 
OCCURRING BY LATE EVENING WITH IMPRESSIVE VALUES OF MID LEVEL -EPV. 
THE GFS IS FURTHER NORTH WITH THE BEST FRONTOGENESIS BUT DOES PAINT 
IMPRESSIVE VALUES OF -EPV AS WELL. DENDRITIC GROWTH LOOKS 
GOOD...WITH 12 TO 22 MICROBARS/SEC IN THE -12C AND -18C LAYER FOR 
MOST LOCATIONS FOR A TIME THIS EVENING INTO THE EARLY OVERNIGHT 
HOURS. THEREFORE...I THINK WE'RE DEALING WITH A PRETTY QUICK MOVING 
AND PARTIALLY CONVECTIVE THUMP OF SNOW HERE TONIGHT...MAINLY FOR THE 
HIGHER ELEVATIONS...BUT NOT SO SURE THE LOWER ELEVATIONS WON'T SEE 
IT FOR A TIME AS WELL.

GAMEPLAN FOR NOW IS THIS...

ANY RAIN OR RAIN/SNOW MIX ABOVE THE 500 FOOT LEVEL QUICKLY GOES TO 
SNOW THIS EVENING AS EVAPORATIONAL COOLING AND STRONG DYNAMIC 
COOLING OCCUR QUITE QUICKLY. THE SNOW WILL BECOME MODERATE TO HEAVY 
FOR AT LEAST A COUPLE OF HOURS BEFORE MIDNIGHT WITH SFC TEMPS AROUND 
THE 32F MARK. WHEN ALL IS SAID AND DONE AFTER MIDNIGHT...EXPECT 
ANYWHERE FROM 2 TO 5 INCHES...LOCALLY 6...TO HAVE FALLEN ACROSS 
THESE HIGHER ELEVATIONS. THE SNOW WILL LIKELY BE WET AND ACT TO 
WEIGH DOWN TREE BRANCHES. WILL BE ISSUING A SNOW ADVISORY FOR THESE 
AREAS. LEFT CENTRAL/EASTERN HAMPDEN COUNTY MASS OUT OF THE ADVISORY 
SINCE MOST OF THAT COUNTY IS OF LOW ELEVATIOPN. LEFT CT COUNTIES OUT 
OF THE ADVISORY FOR NOW AS WELL DUE TO LOWER CONFIDENCE THAT FAR 
SOUTH. HOWEVER...NW HARTFORD COUNTY AS WELL AS WINDHAM/TOLLAND 
COUNTIES WILL HAVE TO BE WATCHED FOR ADVISORY SNOWS AS WELL.

AT LOWER ELEVATIONS...INCLUDING THE CT RIVER VALLEY AND MOST OF 
RI/EASTERN MASS...EXPECT LIGHT RAIN TO MORE GRADUALLY CHANGE OVER TO 
SNOW LATER IN THE EVENING AS BOUNDARY LAYER TEMPS GRADUALLY COOL. 
HOWEVER...ONCE THE CHANGEOVER OCCURS...IT MAY SNOW QUITE HEAVY FOR A 
COUPLE OF HOURS. WENT WITH 1-3" FOR THESE AREAS EXCEPT THE SOUTH 
COAST OF RI/MASS AS WELL AS THE CAPE AND ISLANDS WHERE MAINLY RAIN 
IS EXPECTED. WILL HAVE TO WATCH EASTERN MASS/RI CAREFULLY FOR A BIT 
MORE SNOW THAT FORECAST IF THE BOUNDARY LAYER CAN COOL MORE QUICKLY 
THAN PROGGED.

OTHERWISE...SNOW ENDS WELL BEFORE DAYBREAK SUNDAY. SUNDAY LOOKS TO 
BE PARTLY CLOUDY WITH BELOW SEASONABLE TEMPS EXPECTED.