Storm on track, here’s details from the National Weather Service
My summary: snow, steady into early afternoon, some leftover light snow into the late afternoon.
NWS Forecast Discussion 1049am Tuesday, Dec 10th
.NEAR TERM /UNTIL 6 PM THIS EVENING/…
MAIN STORY TODAY WILL BE MODERATE TO HEAVY SNOW. WINTER WEATHER
ADVISORY REMAINS IN EFFECT FOR ENTIRE FORECAST REGION. ANY DRIER
LOW LEVELS AND TEMPS A FEW DEGREES BELOW FREEZING QUICKLY WET BULB
TO NEAR FREEZING OUT EAST FOR THE TWIN FORKS OF LONG ISLAND AND
SOUTHEAST CT. TEMPS LOWER A DEGREE AND STAY FREEZING OR BELOW
THEREAFTER. THEREFORE SNOW WILL ACCUMULATE. FORCING FOR THIS IS
WELL ESTABLISHED DESPITE THE LACK OF A STRONG SURFACE LOW. DEEP
TROUGH IN THE MID LEVEL WITH POSITIVE VORTICITY ADVECTION AHEAD OF
IT REALLY WILL ENHANCE PRECIP THROUGH THE 18Z HOUR. RUC13 SHOWS
DECENT OMEGA WITHIN THE SNOW GROWTH ZONE BETWEEN -10 AND -20
DEGREES C WITH THE MORNING MODERATE TO HEAVY SNOW MOVING ACROSS.
THE FORCING AND HEAVIEST SNOW IS CONCENTRATED ALONG URBAN NE
NJ…NYC…SOUTHERN LOWER HUDSON VALLEY…SOUTHERN
CONNECTICUT…WESTERN LONG ISLAND CORRIDOR. ADDITIONAL SNOW WITH
GENERALLY LIGHT ACCUMULATIONS EXPECTED AFTER 18Z-19Z WITH
ADDITIONAL FORCING FROM POSITIVE VORTICITY ADVECTION WITH TROUGH
ALTHOUGH AMPLITUDE IS NOT AS HIGH.
OVERALL FOR STORM TOTAL…SNOW AMOUNTS OF 3 TO 5 INCHES WITH
LOCALLY HIGHER AMOUNTS POSSIBLE IN NE NJ…NYC…SOUTHERN LOWER
HUDSON VALLEY…MOST OF SOUTHERN CT…AND MOST OF LONG ISLAND.
ELSEWHERE…3 TO 4 INCHES OF SNOW. AGAIN…LOCALLY HIGHER AMOUNTS
WILL BE POSSIBLE.
ADDITIONAL SNOW WITH GENERALLY LIGHT ACCUMULATIONS EXPECTED AFTER
18Z-19Z WITH ADDITIONAL FORCING FROM POSITIVE VORTICITY ADVECTION
WITH TROUGH ALTHOUGH AMPLITUDE IS NOT AS HIGH.
CONSENSUS OF THE MODELS TAKES THE LOW TO THE SE OF THE 40N/70W
BENCHMARK BY EARLY THIS AFTERNOON. SO THIS…COUPLED WITH ONGOING
LOW LEVEL COLD AIR ADVECTION WILL YIELD A P-TYPE OF SNOW ACROSS
THE ENTIRE CWA.
TEMPERATURES ARE CRITICAL TO THIS FORECAST – EXPECT GENERALLY SLOWLY
FALLING TEMPERATURES THIS MORNING ONCE THE PRECIPITATION BEGINS…AND
THIS WILL CONTINUE INTO THIS AFTERNOON WITH THE WET-BULBING OF
TEMPERATURE – ESPECIALLY NOTING THAT LOWER DEWPOINT AIR IS BEING
ADVECTED IN THE LOWER LEVELS. THIS WILL PLACE NORTHERN ZONES IN THE
MID TO UPPER 20S AND SOUTHERN ZONES AROUND 30. THIS TEMPERATURE FALL
OFF WILL ALLOW FOR RATIOS OF AROUND 12:1 ACROSS SOUTHERN AREAS AND
RAP/NAM/GFS/SREF/ECMWF ALL SHOW AN AREA OF FAIRLY STRONG
FRONTOGENESIS FROM 700-500 HPA CROSSING THE AREA THIS MORNING TO
EARLY AFTERNOON…WITH THE CORE IF IT TRACING FROM JUST W OF NYC ON
NE INTO S CT.
This forecast storm is working 9 to 5 – actually it must be on flextime – closer to 8 to 4, and getting an early start to the west and northwest of NYC. The snow started in DC about 6am. Most areas will see the significant snow start all at once as the storm gets its morning coffee.
The NWS has increased forecast snow amounts to 3 to 5 inches – they haven’t changed the amount of precipitation, it’s just going to be fluffier.
Now we wait for the upper air disturbance to give the little low over the Carolinas a kick, just like your morning coffee. It’s not a big storm – but during the time when a storm develops over as it moves past us offshore, the snowfall rates are highest. Without the upper air ‘kick’ of energy, this would just be a few flurries. But it also means the accumulating snow will end by about 4pm as the new storm gets carried away on the jet steam.