Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 182141
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
541 PM EDT SAT MAR 18 2017

VALID 00Z SUN MAR 19 2017 - 00Z WED MAR 22 2017


...NORTHERN MID ATLANTIC/NORTHEAST...

A WELL-DEFINED MID-UPPER LEVEL SHORTWAVE IS CURRENTLY DIVING
SOUTHEAST FROM THE LOWER GREAT LAKES INTO THE MID ATLANTIC REGION.
EVENTUALLY EXPECT AN ELONGATED AREA OF LOW PRESSURE TO FORM OFF
THE MID ATLANTIC COAST...MOVING WELL OFF THE NEW ENGLAND COAST
THROUGH THE DAY SUNDAY. THE TREND AMONGST THE GUIDANCE HAS BEEN
FOR A FURTHER SOUTH TRACK AND SLOWER PROGRESSION OF THE MID/UPPER
LEVEL LOW AS IT MOVES INTO THE MID ATLANTIC TONIGHT. THIS ENDS UP
RESULTING IN A LOW TRACK FURTHER OFFSHORE OF NEW ENGLAND. STILL
SOME UNCERTAINTY...BUT THE GROWING CONSENSUS IS TO KEEP MOST OF
THE ACCUMULATING SNOWFALL OFFSHORE. ONE EXCEPTION IS THE 12Z GEM
REGIONAL...BUT THAT APPEARS TO BE ON ITS OWN IN KEEPING HIGHER
SNOWFALL INTO SOUTHERN NEW ENGLAND. THE CONSENSUS AMONGST THE
OTHER HIGH RES AND GLOBAL GUIDANCE IS TO GENERALLY LIMIT ANY
ACCUMULATIONS TO CAPE COD AND THE ISLANDS...BUT EVEN THERE QPF IS
LOW AND BOUNDARY LAYER TEMPERATURES ARE MARGINAL. THE MARGINAL
TEMPERATURES COMBINED WITH LIGHT INTENSITY SUGGEST ACCUMULATIONS
COULD BE HARD TO COME BY. THUS AS OF NOW ONLY EXPECTING AT MOST
1-2" ACROSS CAPE COD...ALTHOUGH LOW PROBABILITIES OF 2-4" STILL
EXISTS.

ANOTHER TREND WITH THIS SYSTEM IS FOR GREATER QPF UNDERNEATH THE
MID/UPPER LEVEL LOW AS IT MOVES ACROSS THE MID ATLANTIC...IN A
STRENGTHENING AREA OF LOW/MID LEVEL CONVERGENCE ALONG AN INVERTED
TROUGH AXIS. TEMPERATURES WILL DROP FAIRLY RAPIDLY UNDERNEATH THE
UPPER LOW...WITH MODERATE TO LOCALLY HEAVY PRECIPITATION ALSO
HELPING TO DYNAMICALLY COOL THE PROFILE. THUS WOULD EXPECT TO SEE
A TRANSITION TO WET SNOWFALL ACROSS PORTIONS OF SOUTH CENTRAL PA
INTO MD FROM TONIGHT INTO EARLY SUNDAY. SOME UNCERTAINTY ON
EXACTLY HOW QUICKLY THIS PRECIPITATION WILL TRANSITION TO
SNOW...AND RATIOS WILL LIKELY BE LOW GIVEN THE WARM BOUNDARY LAYER
PROFILES. HOWEVER IT DOES APPEAR INCREASINGLY LIKELY THAT A SWATH
OF 1-3" OF SNOW IS PROBABLE ACROSS PORTIONS OF SOUTH CENTRAL PA
INTO NORTHERN MD. ALSO LOOKS LIKE A TRANSITION TO WET SNOW IS
POSSIBLE FURTHER SOUTH TOWARDS DC AND PORTIONS OF EASTERN VA AND
WESTERN MD. THIS TRANSITION WILL LIKELY BE TIED TO PRECIPITATION
INTENSITY...WITH ANY HEAVIER RATES PROBABLY ALLOWING FOR A MIX OR
CHANGEOVER TO SNOW. THE DURATION OF SNOW WILL PROBABLY BE LIMITED
IN THESE AREAS...WITH PRECIPITATION COMING TO AN END SHORTLY AFTER
PROFILES COOL ENOUGH FOR A TRANSITION. ALSO WITH THE BOUNDARY
LAYER REMAINING WARM...CURRENTLY NOT EXPECTING ANY ACCUMULATIONS
OF 1" OR GREATER ALONG I95 AND POINTS SOUTH. ALTHOUGH WILL HAVE TO
CONTINUE TO MONITOR SHORT TERM TRENDS.

ALSO LIKELY TO SEE UPSLOPE SNOW SHOWERS ACROSS THE HIGHER TERRAIN
OF EASTERN WV  AS WINDS TURN NORTHWESTERLY. 3-6" SEEMS POSSIBLE
ACROSS THE HIGHEST PEAKS...WITH A BROADER 1-3" AREA.

...WESTERN U.S....

WARM TEMPERATURES WILL RESULT IN HIGH SNOW LEVELS ACROSS THE
WEST...LIMITING SNOWFALL AMOUNTS. ON DAY 2 (0Z MON-0Z TUE)
ACCUMULATING SNOWFALL SHOULD BE CONFINED TO PORTIONS OF NORTHWEST
MT...WITH LIGHT WAA SNOWFALL AND TERRAIN ENHANCEMENT LIKELY OVER
THIS AREA. A BIT MORE COVERAGE BY DAY 3 (OZ TUE-0Z WED) AS
TROUGHING APPROACHES THE WEST. QUITE A BIT OF MOISTURE IS
PREDICTED TO MOVE ASHORE WITH THIS FEATURE...WHICH COMBINED WITH
DIFFLUENT FLOW ALOFT AND FORCING AHEAD DO THE TROUGH AXIS...SHOULD
RESULT IN WIDESPREAD MODERATE TO HEAVY PRECIPITATION TOTALS ON DAY
3. SNOW LEVELS WILL REMAIN HIGH HOWEVER...WITH HIGHEST
ACCUMULATIONS LIKELY ACROSS THE HIGHEST TERRAIN OF THE CENTRAL
SIERRAS (6"+) AND LESSER AMOUNTS ACROSS PORTIONS OF THE WA
CASCADES.

A LIGHTER RAIN/SNOW MIX MAY ALSO SPILL EAST INTO PORTIONS OF THE
WESTERN PLAINS ON TUESDAY AS WARM AIR OVERRIDES THE STRONG
BAROCLINIC ZONE IN PLACE. THIS MAY RESULT IN SOME LIGHT SNOW
ACCUMULATIONS INTO PORTIONS OF SD/NE.

CHENARD

$$





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