Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 312011
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
410 PM EDT FRI OCT 31 2014

VALID 00Z SAT NOV 01 2014 - 00Z TUE NOV 04 2014

DAYS 1-3...

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

A POWERFUL STORM SYSTEM OUT OVER THE PACIFIC WILL CONTINUE TO
GRADUALLY MOVE ONSHORE.  IN ADVANCE OF THE UPPER TROUGH...A JET
STREAK WILL CROSS CENTRAL CA AND CENTRAL TO NORTHERN NV.  PACIFIC
MOISTURE TRANSPORT WITH VERY FAVORABLE OROGRAPHICS WILL PRODUCE
MUCH-NEEDED PRECIPITATION WITH SNOW ACROSS THE CENTRAL AND
SOUTHERN SIERRA.   SEVERAL INCHES ARE EXPECTED WITH UP TO A FOOT
OF SNOW IS POSSIBLE NEAR THE SIERRA CREST ON SAT.  AS THE UPPER
TROUGH CROSSES INTO THE GREAT BASIN...A SURFACE LOW WILL FORM AND
UPPER LEVEL DIVERGENCE/MID LEVEL DEFORMATION IS MAXIMIZED OVER
CENTRAL ID TO WESTERN MT.  DURING THIS TIME THE MODELS SHOW A
SPLIT IN THE FLOW WITH A NORTHERN STREAM WAVE LIFTING INTO
SOUTH-CENTRAL CANADA SUN NIGHT-EARLY MON AND A TRAILING SOUTHERN
STREAM WAVE OVER THE SOUTHWEST.  WHILE THE THREAT FOR HEAVY SNOW
IS FORECAST TO DIMINISH ACROSS THE NORTHERN ROCKIES ON MON...IT IS
EXPECTED TO INCREASE ACROSS 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 FOCUSES ACROSS THE RANGES OF WESTERN CO.  WPC
RELIED MORE HEAVILY ON THE NAM/ECMWF FOR THEIR CONSISTENCY AND
RESOLUTION THROUGH THE PERIOD.

...CENTRAL/SOUTHERN APPALACHIANS...

A ZONE OF MID LEVEL CYCLONIC VORTICITY ADVECTION IS CURRENTLY
DROPPING INTO THE OH AND TN VALLEYS WHILE AN AREA OF ENHANCED
MOISTURE AND ASCENT IN ADVANCE OF THE 700 MB FRONT PRODUCES
PRECIPITATION. THE FIRST SIGNIFICANT SNOW OF THE SEASON APPEARS
LIKELY TONIGHT-EARLY SAT ACROSS PARTS OF THE CENTRAL/SOUTHERN
APPALACHIANS. THE DYNAMIC SHORTWAVE TROUGH WILL PRODUCE A BAND OF
WELL-DEFINED MID LEVEL DEFORMATION THAT ROTATES ACROSS THE CENTRAL
TO SOUTHERN APPALACHIANS. A POCKET OF ENHANCED VERTICAL LIFT AND
VERY COLD ANOMALOUS AIR ALOFT WILL SURGE ACROSS THE APPALACHIAN
SPINE TO COMBINE WITH UPSLOPE FLOW FOR SNOWFALL IN THE MOUNTAINS
AND ONLY MINOR ACCUMULATIONS AWAY FROM THE TERRAIN.  WITH THE
MODEL/FORECAST REMAINING IN GOOD AGREEMENT....WPC RELIED HEAVILY
ON A BLEND OF CONTINUITY OF THE LATEST NAM..SREF AND ECMWF FOR QPF
AND TEMPERATURE PROFILES USED IN GENERATING SNOW
AMTS/PROBABILITIES.  SNOW SHOULD DECREASE IN COVERAGE/INTENSITY ON
SAT AS THE UPPER TROUGH DEPARTS THE MOUNTAINS OVER LOWER
ELEVATIONS AND THEN THE COAST.

...MAINE...

WHILE LATITUDINAL DIFFERENCES REMAIN...MODELS CONTINUE TO CONVERGE
UPON THE IDEA OF A NARROW STRIPE OF HEAVY SNOW...WITH AMOUNTS OF
UP TO A FOOT ACROSS SOME PORTION OF EASTERN MAINE.  THE MODELS
INDICATE A PAIR OF LOWS TO FORM OVER THE WESTERN ATLANTIC.  THE
FIRST LOW MOVES NORTH OVER THE OPEN WATERS WITH UPPER DIVERGENCE
DEVELOPING/MID LEVEL FRONTOGENESIS OVER MAINE AS A JET STREAK
CROSSES EASTERN MAINE AND ADJACENT COASTAL WATERS.  SNOW IS
EXPECTED TO DEVELOP WITHIN THE FRONTAL CIRCULATION WITH SEVERAL
INCHES POSSIBLE.  ON SUN THE SECOND LOW AT THE BASE OF THE UPPER
TROUGH INTENSIFIES AND BECOMES THE PRIMARY LOW.  MODELS GENERALLY
AGREE THAT AN UPPER DIVERGENCE/MID LEVEL FRONTOGENESIS SIGNATURE
WILL CONTRIBUTE TO BANDED MODERATE TO HEAVY SNOW...HOWEVER
DIFFERENCES WITH RESPECT TO THE LOW TRACK CONTRIBUTE TO LOWER
CERTAINTY AS TO WHERE THIS HEAVIER AXIS WILL FALL.  WHILE THE GFS
HAS MADE SOME ADJUSTMENT TO THE EAST...IT CONTINUES TO TRACK LEFT
OF THE MAJORITY OF THE DETERMINISTIC MODELS.  THE WPC FORECAST
FELL MORE IN LINE WITH LINE WITH THE CONSENSUS WHICH WAS BEST
REPRESENTED BY A NAM/ECMWF BLEND.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PEREIRA



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