Quantitative Precipitation Forecast
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FOUS11 KWBC 140839
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
338 AM EST TUE FEB 14 2017

VALID 12Z TUE FEB 14 2017 - 12Z FRI FEB 17 2017


NORTHEAST/NEW ENGLAND...

SLIGHT DIFFERENCES IN TIMING AND STRENGTH WITH THE CLOSED LOW
CROSSING NEW ENGLAND WEDNESDAY AND THEIR ACCOMPANYING TRANSFER OF
THE INLAND LOW TO A DEEPER LOW IN THE GULF OF MAINE WEDNESDAY
NIGHT SUPPORT MODEST SPREAD IN THE PLACEMENT/AMOUNTS/STRUCTURE OF
THE RESULTING HEAVY SNOWFALL...WITH THE CENTROID OR MEAN OF THE
SOLUTIONS FOCUSED ACROSS EASTERN NEW HAMPSHIRE/SOUTHWEST MAINE
WEDNESDAY AND WEDNESDAY NIGHT. CONCERNING THE
PROBABILITIES...MODERATE PROBABILITIES OF 12 INCHES AND HIGH
PROBABILITIES OF 8 INCHES ARE DEPICTED ACROSS EASTERN NEW
HAMPSHIRE AND SOUTHWEST MAINE WEDNESDAY INTO WEDNESDAY
NIGHT...WITH HIGH PROBABILITIES OF 4 INCHES DOWNWIND OF LAKES ERIE
AND ONTARIO. FOR THE PROBABILITIES OF 12 INCHES...THE MAJORITY OF
SREF ARW CORE MEMBERS WERE FURTHER INLAND WITH THE COASTAL
LOW...RESULTING IN A NORTHWESTWARD SHIFT TO THEIR SNOW
AXES...COMPARED TO THE SREF NMMB/GEFS/ECMWF ENSEMBLES WHICH WERE
REASONABLY WELL-CLUSTERED SOUTHWESTWARD WHERE THE DETERMINISTIC
WWD AMOUNTS SHOW THE HIGHEST AMOUNTS. LIKEWISE...THE MAJORITY OF
ECMWF ENSEMBLE MEMBERS SHOW VERY LOW PROBABILITIES OF 8 AND ZERO
PROBABILITY OF 12 INCHES FOR NORTHERN MAINE...DUE LARGELY TO THEIR
MORE SOUTHWESTWARD AND SLOWER LOW TRACK. MOST OF THE GEFS MEMBERS
ARE FASTER AND SLIGHTLY NORTH OF THE ECMWF...WHICH SUPPORT HIGHER
PROBABILITIES OF HIGHER SNOW TOTALS FOR NORTHERN MAINE. GIVEN THE
REMAINING MODEL SPREAD...CONFIDENCE IS ONLY AVERAGE FOR THIS
EVENT.

THE PROBABILITY OF 0.25 INCHES OF ICE IS LESS THAN 10 PERCENT.

NORTHWEST/CALIFORNIA/N. ROCKIES...

THERE`S A 10 TO 40 PERCENT CHANCE OF 0.25 INCHES OR MORE OF ICE
ACROSS INTERIOR WASHINGTON ON
WEDNESDAY...INCLUDING THE MOUNTAIN PASSES...ALTHOUGH THE EVENT MAY
BEGIN TUESDAY NIGHT. THE SREF NMMB MEMBERS ARE HEAVIEST WITH ICE
IN PART TO A MUCH WETTER SOLUTION FOR THE INTERIOR COMPARED WITH
THE OTHER GUIDANCE. THE WPC WWD INTERNAL ICE AMOUNTS ARE MUCH LESS
THAN THE SREF NMMB MEMBERS...AND CLOSER TO A CONSENSUS OF THE
LIGHTER SREF ARW CORE MEMBERS...AS WELL AS THE GEFS/ECMWF ENSEMBLE
MEMBERS.

ELSEWHERE...MOUNTAIN SNOWS WILL OVERSPREAD MUCH OF THE WEST
THURSDAY INTO FRIDAY...WITH LOW TO MODERATE PROBABILITIES OF 12
INCHES ACROSS NORTHERN CASCADES/SAWTOOTH/SIERRAS...AND MODERATE TO
HIGH PROBABILITIES OF 4 INCHES ACROSS LOWER MOUNTAIN ELEVATIONS OF
THE OREGON CASCADES...AS WELL AS THE BITTERROOTS. OVERALL...THE
MODEL SPREAD IS NEAR TO SLIGHTLY ABOVE AVERAGE...AND IS
ACCOMPANIED BY NEAR TO BELOW AVERAGE CONFIDENCE DUE TO THE STRONG
ZONAL FLOW ACROSS THE PACIFIC THAT IS ASSOCIATED WITH CONSIDERABLE
RUN-TO-RUN VARIABILITY IN THE MODEL DETAILS.

CENTRAL-SOUTHERN APPALACHIANS...

THERE IS LESS THAN A 10 PERCENT CHANCE OF RECEIVING 4 INCHES OF
SNOW AT ELEVATIONS ABOVE 3000 FT LATE TUESDAY NIGHT THROUGH MID
WEDNESDAY MORNING. DETERMINISTIC WWD TOTALS DEPICT BETWEEN 1 AND 2
INCHES...ALTHOUGH THE SPREAD IS MODEST DUE TO DIFFERENCES IN
PRECIPITATION ACCOMPANYING THE LOW MOVING ACROSS THE
SOUTHEAST...WHICH THE MODELS SHOW WITH DIFFERENT INTENSITIES AND
SPEED. THE NAM WAS GENERALLY RULED OUT DUE ITS STRONGEST AND MOST
NORTHERN LOW...WHICH MAY BE A LINGERING RESULT OF THE PRECEDING
CONVECTION ACROSS TEXAS. RATHER THAN THE NAM...THE 12-00Z
ECMWF/00Z GFS/12Z PARALLEL GFS/00Z UKMET ARE MOST PREFERRED DUE TO
THEIR WEAKER/FASTER SOLUTION THAT OFTEN ACCOMPANIES UPSTREAM
MID/UPPER LEVEL CONFLUENCE. 1 OF THE SREF/8 OF THE 20 GEFS/ZERO OF
THE 50 ECMWF MEMBERS SUPPORT 4 INCHES OF SNOW OVER EXTREME
SOUTHWEST VIRGINIA...WHICH IS A PROBABILITY OF 9
PERCENT...ALTHOUGH THE ACTUAL PERCENTAGE OF 4 INCHES IS LESS THAN
9 PERCENT GIVEN THE MODE IS JUST 1 TO 2 INCHES.

THE PROBABILITY OF 0.25 INCHES OF ICE IS LESS THAN 10 PERCENT.

JAMES


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