Heads UP! More snow if the change to rain is late

9am UPDATE… Radar shows an area of snow that has popped up north of NYC – the NWS thinks this and similar bands can give a quick 1 to 2 inches of snow before 11am……

Original post….
Snow has begun in the northeast, a snowfall I almost can’t see out the window.
The flakes are so small, with the very cold air, but they are accumulating slowly.

Expect snow on and off this morning, slowly accumulating, with the heavier snow starting around sundown. The heaviest snow will fall by midnight, with warm air sliding around the storm and changing the snow to rain.

Depending on how soon and how strong the warm air arrives will determine the amount of snow to fall.

The NYC forecast discussion notes that each run of the computer models has brought more warm air into the northeast, so they may reduce the snowfall amounts in later forecasts.
Here’s links to the forecast amount maps, so if they change you can see the latest version:
New England:
http://www.erh.noaa.gov/box/StormTotalSnow/index.php
New York City Metro:
http://www.erh.noaa.gov/okx/stormtotalprecip.php
Example for NYC – click to enlarge:
StormTotalSnowFcst nyc 14 dec 7am
Philadelphia:
http://www.erh.noaa.gov/phi/StormTotalSnow/stormtotal.php
Washington/Baltimore:
http://www.erh.noaa.gov/lwx/winter/
Albany:
http://www.erh.noaa.gov/aly/Past/Snow_PNS/WSW.htm
Bingingham:
http://www.erh.noaa.gov/bgm/
Rochester:
http://www.erh.noaa.gov/buf/gfemaps/StormTotalSnow.shtml

Details from the 7am forecast discussion for the NYC area:
MODELS HAVE COME INTO GOOD AGREEMENT WITH THE DEVELOPMENT AND
TRACK OF THE COASTAL LOW LATER TODAY INTO TONIGHT.
. . . . .
THE COMPLICATING FACTOR OR QUESTION FOR THIS STORM IS AT WHAT TIME DOES THE
CHANGEOVER TO RAIN HAPPEN AT THE COAST…AND THEN TO FREEZING
RAIN INLAND. THE COAST LOOKS TO BE SOMEWHERE IN THE 00Z (7pm) TO 03Z (10pm)
TIMEFRAME…WITH INLAND AREAS FROM 03Z (10am) TO 09Z (4am). AT THE COAST…THE
TIME OF CHANGEOVER COINCIDES WITH THE TIME OF THE BEST FORCING AND
HEAVIEST PCPN. SO IF IT HAPPENS AS EARLY AS 00Z (7pm)…THERE MAY ONLY
BE INCH OR TWO ACROSS LI/NYC…WHILE A COUPLE OF MORE HOURS LATER
COULD RESULT IN AS MUCH 4 OR 5 INCHES. THIS CHANGEOVER TIME WILL
ALSO BE CRITICAL INLAND AS THE RAIN/SNOW LINE ADVANCES NORTH WITH
THE AID OF A 50 TO 60 KT LOW-LEVEL JET OUT OF THE E/SE. 85H (1km altitude) WINDS
FOR THIS EVENT ARE SOUTHERLY AND STEADILY STRENGTHEN THROUGH THE
DAY…THUS THE ERODING OF THE COLD AIR AND THE CHANGEOVER TO
LIQUID. THE SECONDARY LOW DOES NOT TAKE OVER IN TIME TO MAINTAIN
THE DEEP COLD POOL OVER THE AREA THAT STARTS THE DAY.

THE HEAVIEST PCPN WILL FALL TONIGHT…IN THE 00Z TO 12Z (7am to 7am )TIMEFRAME
WITH SNOWFALL ACCUMULATIONS IN THE INTERIOR OF 6 TO 8
INCHES…AND AS LOW AS 2 TO 4 INCHES ACROSS COASTAL LI. A TENTH TO
ONE-QUARTER INCH OF ICE IS FORECAST ACROSS THE INTERIOR WITH
POSSIBLE HIGHER AMOUNTS SHOULD THE CHANGEOVER TO FREEZING RAIN
OCCURS SOONER. LIQUID EQUIVALENT WILL BE AROUND AN INCH FOR MOST
LOCATIONS. AMOUNTS MAY APPROACH 1.50 INCHES ACROSS EASTERN LI AND
SE CT.

MODEL TRENDS CONTINUE TO BE WARMER AND THIS MAY RESULT IN
SUBSEQUENT FORECAST AMOUNTS OF SNOWFALL BEING LOWERED.

TEMPS TODAY WILL BE MAINLY IN THE 20S AND MAY ACTUALLY FALL A FEW
DEGREES WITH THE ONSET OF THE SNOW. AS THE SECONDARY LOW TAKES
SHAPE THIS AFTERNOON…THE NE FLOW WILL VEER AROUND TO THE EAST
AND STEADILY STRENGTHEN THROUGH THIS EVENING AT 15 TO 25
MPH…WITH GUSTS UP TO 40 MPH.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/…
ONLY A LOW CHANCE OF LINGERING PCPN BY SUNDAY MORNING

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s