Quantitative Precipitation Forecast
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000
FOUS11 KWBC 302048
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
448 PM EDT THU OCT 30 2014

VALID 00Z FRI OCT 31 2014 - 00Z MON NOV 03 2014

DAYS 1-3...

CALIFORNIA/INTERMOUNTAIN WEST/NORTHERN ROCKIES...

A POWERFUL STORM SYSTEM OUT OVER THE PAC WILL GRADUALLY SPLIT ON
FRI ALLOWING THE SRN STREAM TO TAKE OVER ON SAT AND AN AGGRESSIVE
JET STREAK TO SLICE INTO CENTRAL CA AND NV BEFORE REACHING THE
INTER-MOUNTAIN WEST. SOME DECENT PAC MOISTURE TRANSPORT WITH VERY
FAVORABLE OROGRAPHICS SUGGEST MUCH NEEDED PRECIPITATION WITH SNOW
ACROSS THE CENTRAL/SRN SIERRA. IN FACT... A WPC BLEND OF THE
GLOBAL MODELS SUGGEST HEAVY SNOW PROBS OF UP TO A FOOT POSSIBLE.
AS THE UPPER DYNAMICS REACH THE INTER-MOUNTAIN WEST... A SURFACE
LOW WILL FORM AND RAPID INTENSIFICATION IS ANTICIPATED. A CLOSED
MID TO UPPER LOW SHOULD RESULT OVER THE NRN ROCKIES ON SUN AND
SETUP A ZONE OF HEAVY DYNAMIC COOLING/DEFORMATION AREA SNOWS WITH
OROGRAPHIC ENHANCEMENT FOR SIGNIFICANT ACCUMULATIONS FOR THE NRN
ROCKIES INTO THE TETONS/ABSAROKAS AND EVEN BITTERROOTS. WPC STAYED
VERY CLOSE TO A BLEND OF THE ECMWF WITH THE INTERNAL PSEUDO BIAS
CORRECTED GUIDANCE FOR HEAVY SNOW PROBS.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


UPPER GREAT LAKES TO CENTRAL/SOUTHERN APPALACHIANS TO MAINE...

A POTENT VORT WILL DIVE FROM WESTERN ONTARIO INTO THE
UPPER/WESTERN GREAT LAKES LATE THURS/EARLY FRI BEFORE PROCEEDING
INTO THE OH/TN
VALLEYS. THE DRAMATIC COLD ADVECTION ASSOCIATED WITH THIS SHORT
WAVE WILL PLUMMET SOUTH AND EAST FROM THE UPPER MS VALLEY/GREAT
LAKES TO THE SRN APPALACHIANS AND THE MOST OPPORTUNE PERIOD FOR
HEAVY SNOW APPEARS TO BE FROM THURS NIGHT TO FRI MORNING. A MODEST
DYNAMIC COOLING REGIME ON THE BACKSIDE OF DEVELOPING SURFACE LOW
PRESSURE AND COLD AIR ALOFT INTERACTING WITH THE WARM LAKES SHOULD
RESULT IN RAIN TO RAIN/SNOW AND POSSIBLE SNOW ACCUMULATIONS ACROSS
THE UP OF MI AND NRN LOWER MI. A BLEND OF THE NAM/ECMWF FOR QPF
AND THERMAL PROFILES SUGGEST ONLY A LOW PROB OF 4 INCHES.

THE FIRST SNOW OF THE SEASON APPEARS IMMINENT ON SAT ACROSS PARTS
OF THE CENTRAL/SRN APPALACHIANS WITH POTENTIALLY SIGNIFICANT
AMOUNTS. THE DYNAMIC SHORT WAVE TROUGH CARVING THROUGH THE GREAT
LAKES ON FRI WILL BOTTOM-OUT IN THE BASE OF THE LONG WAVE UPPER
TROUGH EXTENDING DOWN INTO THE SERN STATES. A POCKET OF ENHANCED
VERTICAL LIFT AND VERY COLD ANOMALOUS AIR ALOFT WILL SURGE ACROSS
THE OH VALLEY AND APPALACHIAN SPINE TO COMBINE WITH UPSLOPE FLOW
FOR STEADY SNOWFALL IN THE MTNS AND ONLY MINOR ACCUMULATIONS AWAY
FROM THE TERRAIN. THE MODEL/FORECAST SPREAD HAS NARROWED
CONSIDERABLY AND WPC RELIED HEAVILY ON THE OPERATIONAL GFS/ECMWF
WITH THE INTERNAL PSEUDO BIAS CORRECTED GUIDANCE/MEAN FOR 4 AND 8
INCH HEAVY SNOW PROBS.

THE UPPER TROUGH OVER THE EAST WILL NEG TILT ON SUN... AS THE
UPPER DYNAMICS IN THE BASE OF THE UPPER TROUGH/OVER THE SOUTHEAST
WILL TRANSFER TO THE COAST AND ALLOW A SURFACE LOW TO FORM OFF THE
NC COAST. THIS WAVE WILL DEEPEN RAPIDLY OFF THE EAST COAST AND
LIFT TOWARD NOVA SCOTIA... WHILE ITS PRECIP SHIELD BACKS INTO THE
EXPANDING COLD SECTOR FOR HEAVY SNOWFALL ACROSS MUCH OF MAINE. THE
HEAVIEST TOTALS APPEAR LIKELY ACROSS ERN MAINE... THOUGH THERE IS
SOME SPREAD WITH THE GLOBAL MODELS. WPC FOLLOWED A COMPROMISE OF
THE GFS/ECMWF FOR 4 AND 8 INCH HEAVY SNOW PROBS.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


MUSHER



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