Quantitative Precipitation Forecast
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FOUS11 KWBC 010753
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
352 AM EDT SAT NOV 01 2014

VALID 12Z SAT NOV 01 2014 - 12Z TUE NOV 04 2014

DAYS 1-3...

...INTERMOUNTAIN WEST/NORTHERN AND CENTRAL ROCKIES...

A DEEP UPPER TROUGH IS FCST TO BE ONSHORE IN CA THIS MORNING. A
700 MB LOW DOWNSTREAM NEAR THE NV/OR BORDER AT 12Z THIS MORNING
MOVES NORTHEAST ACROSS ID AND WESTERN MT TONIGHT. MODEST COUPLING
OF NORTHERN AND SOUTHERN STREAM JET STREAKS LEADS TO UPPER
DIVERGENCE MAXIMA
/MID LEVEL DEFORMATION BEING MAXIMIZED OVER CENTRAL ID TO WESTERN
MT.  ON SUNDAY THE PRIMARY 700 MB LOW MOVES OUT OF MT INTO THE
CANADIAN PRAIRIES.  THE DEPARTURE OF THIS LOW LEADS TO A
DIMINISHING THREAT ACROSS THE NORTHERN ROCKIES ON MON.
DIFFERENCES IN TIMING OF THE LOW CONTINUE TO DRIVE HOW LONG THE
SYSTEM REMAINS A THREAT TO PRODUCE SNOW AS THE TREND FOR LATER IN
THE PERIOD IS FOR DRYING AND THE END OF THE EVENT.

THE THREAT FOR HEAVY SNOW SHIFTS FURTHER SOUTH INTO THE CENTRAL
ROCKIES AS THE SOUTHERN STREAM WAVE IS FORECAST TO LIFT THROUGH
THE FOUR-CORNERS REGION.  LEFT-EXIT REGION UPPER JET DYNAMICS
ALONG WITH LOW-MID LEVEL FRONTOGENESIS AND OROGRAPHIC EFFECTS ARE
EXPECTED TO CONTRIBUTE TO HEAVIER AMOUNTS ACROSS THE RANGES OF
WESTERN CO.  MANUAL PROGS BLENDED CONTINUITY AND A CONSENSUS OF
THE 00Z MODELS AND 21Z SREF MEAN QPF/TEMP PROFILES. THE TIMING OF
THE DEPARTURE OF THE UPPER TROUGH WILL DETERMINE THE EXTENT OF
LINGERING SNOW SHOWERS EARLY ON DAY 3 (MON).  THE UPPER TROUGH
PASSAGE LEADS TO CESSATION OF RISING MOTION AND TRANSITION TO
SINKING MOTION AND DRYING AIRMASS...SO SNOW SHOULD SUBSIDE AS DAY
3 PROGRESSES.


...MAINE...

MODELS SHOW A PAIR OF LOWS IN THE COASTAL TO OFFSHORE WATERS WITH
THE INITIAL SURGE OF 700 MB ASCENT OCCURRING AS THE FIRST LOW
MOVES NORTH AND THE 700 MB FRONT SETTING UP ACROSS MAINE.  SNOW
DEVELOPS AS COLD AIR IS INGESTED INTO THE SYSTEM AS IT DEEPENS
WITH WET BULB COOLING OCCURRING AS WELL. UNCERTAINTY PERSISTS IN
DOWNEAST MAIN AS INITIAL CONDITIONS ARE TOO WARM FOR SNOW...WITH
THE COLD AIR MORE LIKELY TO MAINTAIN SUSTAINED SNOW FURTHER
INLAND. ON DAY 2 (SUN)...A LARGE UPPER DIVERGENCE/MID LEVEL
CONVERGENCE COUPLET THE FIRST SEVERAL HOURS OF THE PERIOD SHOULD
PRODUCE A NARROW STRIPE OF HEAVY SNOW...WITH AMOUNTS UP TO A FOOT
ACROSS PORTIONS OF EASTERN MAINE.

THIS SECOND LOW ON DAY 2 BECOMES STRONG AND THUS HEAVIER AMOUNTS
ARE INDICATED ON DAY 2 AS MID LEVEL FRONTOGENESIS AIDS ASCENT.
DIFFERENCES BEGIN TO DEVELOP AS THE 00Z NAM IS ON THE LEFT SIDE OF
THE SUITE OF TRACK OPTIONS...AND CANADIAN GLOBAL ON THE RIGHT.
THE 00Z GFS/UKMET/ECMWF FORM THE MIDDLE CLUSTER AND THUS FORM THE
PREFERRED SUITE OF SOLUTIONS.  AS THE LOW GOES BY..ENHANCED COLD
ADVECTION ALLOWS THE RAIN TO SNOW TRANSITION ZONE TO MOVE EAST
TOWARDS THE COAST.  THE TYPICAL TRACK UNCERTAINTY IS AUGMENTED BY
PRECIP TYPE UNCERTAINTY AND SHARP QPF GRADIENTS SO THE FORECAST IS
NOT A CONFIDENT ONE TONIGHT.

...CENTRAL/SOUTHERN APPALACHIANS...

SNOW HAS BEGUN IN THE HIGHER ELEVATIONS IN EASTERN TN AND WESTERN
NC. A ZONE OF MID LEVEL DEFORMATION CONTINUES INTO THIS MORNING
BEFORE THE 700 MB CIRCULATION DEPARTS FOR THE COAST AND ASCENT
SUBSIDES THIS AFTERNOON.  THE SUBSIDENCE RESULTS IN DRYING AND
THEN A SHARP DECREASE IN SNOWFALL COVERAGE AND INTENSITY.  COLD
AIR ALOFT WILL SURGE ACROSS THE APPALACHIAN SPINE WITH DEFORMATION
LIFT AIDED BY WITH UPSLOPE FLOW FOR SNOWFALL IN THE MOUNTAINS AND
ONLY MINOR ACCUMULATIONS AWAY FROM THE TERRAIN.  WITH THE
FORECASTS REMAINING IN GOOD AGREEMENT....WPC RELIED HEAVILY ON A
BLEND OF CONTINUITY WITH THE 21Z SREF MEAN/00Z WRF ARW QPF AND
TEMPERATURE PROFILES TO GENERATE SNOW AMTS/PROBABILITIES.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PETERSEN



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