Quantitative Precipitation Forecast
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FOUS11 KWBC 232224
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
523 PM EST MON JAN 23 2017

VALID 00Z TUE JAN 24 2017 - 00Z FRI JAN 27 2017

DAYS 1-3...

...GREAT BASIN AND CENTRAL/SOUTHERN ROCKIES...

TROUGHING OVER THE WEST WILL CONTINUE A SNOW THREAT INTO TUESDAY.
HOWEVER BY LATER TUESDAY WILL GENERALLY SEE A DECREASE IN SNOWFALL
COVERAGE AND INTENSITY AS THE TROUGH PUSHES INTO THE PLAINS AND
MID/UPPER LEVEL RIDGING BEGINS DEVELOPING ALONG THE WEST COAST.
OVERALL MODELS WERE IN GOOD AGREEMENT...WITH WPC SNOWFALL STAYING
CLOSE TO THE MODEL CONSENSUS. MODERATE TO HIGH PROBABILITIES OF 6"
WILL BE FOCUSED ACROSS THE HIGHER TERRAIN OF NORTHWEST WY INTO
NORTHERN UT...AS WELL AS ACROSS THE COLORADO ROCKIES AND THE
MOGOLLON RIM OF AZ.

...NORTHERN PLAINS/UPPER MS VALLEY AND UPPER GREAT LAKES...

AS TROUGHING MOVES INTO THE PLAINS EXPECT TO SEE AN AREA OF
SURFACE LOW PRESSURE MOVE ACROSS THE CENTRAL PLAINS ON
TUESDAY...INTO THE GREAT LAKES REGION ON WEDNESDAY. THE
COMBINATION OF FORCING AHEAD OF THE MID LEVEL
SHORTWAVE...INCREASING SOUTHEASTERLY LOW LEVEL FLOW WRAPPING
MOISTURE AROUND THE LOW...AND INCREASING LOW/MID LEVEL
FRONTOGENESIS TO THE NORTH OF THE LOW...SHOULD SUPPORT A SHIELD OF
SNOW ACROSS PORTIONS OF SD/NE/MN/IA/WI. THE FRONTOGENESIS AND
NEGATIVE EPV SIGNATURE DOES SUPPORT SOME BANDING OF THE SNOWFALL
RESULTING IN POCKETS OF HEAVY SNOW WITHIN THE BROAD SHIELD OF
MODERATE SNOWFALL. SOME MODEL DIFFERENCES STILL REMAIN WITH
REGARDS TO THE TRACK OF THE LOW AND HOW FAR NORTH OR SOUTH THE
AXIS OF HEAVIEST SNOW ENDS UP. ON DAY 1 (0Z TUE-0Z WED) LEANED OUR
FORECAST CLOSER TO THE MORE CONSISTENT AND FURTHER SOUTH
ECMWF/UKMET SOLUTION. THE NAM IS ALSO NOT TOO FAR OFF...ALTHOUGH
PROBABLY A BIT TOO HEAVY FOR THIS TIME PERIOD. CONTINUED TO THINK
THE 12Z GFS IS TOO FAR NORTH...WITH IT GENERALLY CONTINUING TO
TREND SOUTH CLOSER TO THE NAM/ECMWF/UKMET AXIS. BY DAY 2 (0Z
WED-0Z THU) WE STAYED CLOSER TO THE 06Z GEFS MEAN AND 0Z ECMWF
ENSEMBLE MEAN POSITION...WHICH WAS GENERALLY BETWEEN THE FURTHER
NORTH GFS ND SOUTH ECMWF. THE 0Z UKMET WAS ALSO GENERALLY
REPRESENTATIVE OF OUR PREFERRED CONSENSUS.

WPC SNOWFALL PROBABILITIES SHOW A MODERATE TO HIGH RISK OF 6"-10"
FROM THIS SYSTEM STRETCHING ALONG AN AXIS CENTERED AROUND THE
SD/NE BORDER EAST TOWARDS THE MN/IA BORDER. SOME AMOUNTS AROUND A
FOOT ARE POSSIBLE EMBEDDED WITHIN THE CORE OF THIS SNOWFALL AXIS
AS WELL. GIVEN THE UNCERTAINTY ON THE EXACT AXIS OF
SNOWFALL...UNCERTAINTY ON THE NORTHERN/SOUTHERN GRADIENT REMAINS
ABOVE AVERAGE. SEE OUR PROBABILITY GRAPHICS FOR MORE DETAILS ON
EXACT SNOWFALL PROBABILITIES ACROSS THESE LOCATIONS.

...INTERIOR NEW YORK/NORTHERN PA AND NJ/ NEW ENGLAND...

AN AREA OF LOW PRESSURE WILL MOVE FROM OFF THE MID ATLANTIC COAST
THIS EVENING TO OFF THE NEW ENGLAND COAST THROUGH THE DAY TUESDAY.
PLENTY OF MOISTURE WILL BE WRAPPED BACK INTO THE STORM...WITH THE
UPPER LEVELS ALSO BECOMING INCREASINGLY DIFLUENT. THUS WOULD
EXPECT TO SEE A SWATH OF MODERATE TO LOCALLY HEAVY PRECIPITATION
MOVE NORTHEAST ACROSS THE REGION THROUGH TUESDAY. OVERALL MODEL
DIFFERENCES WITH THE TRACK OF THE LOW AND EVOLUTION OF THE SYSTEM
ARE NOT TOO BIG. HOWEVER THERE ARE PRETTY SIGNIFICANT THERMAL
FIELD DIFFERENCES WITH REGARDS TO HOW MUCH WARM AIR ALOFT IS
ADVECTED NORTH TO THE EAST NORTHEAST OF THE 800-700 MB LOW.

OVERALL TEND TO LEAN A BIT MORE TOWARDS THE NAM THERMAL PROFILES
IN SITUATIONS LIKE THIS SINCE IT TENDS TO DO A BETTER JOB WITH THE
NORTHWARD PUSH OF THE WARM NOSE ALOFT. THUS DID IN GENERAL LEAN
THIS FORECAST MORE TOWARDS THE NAM/SREF THERMAL PROFILES. HOWEVER
THE GFS/ECMWF WERE QUITE A BIT COLDER ALOFT...PRODUCING MORE IN
THE WAY OF SNOW AND LESS IN THE WAY OF FREEZING RAIN/SLEET THAN
THE NAM. THUS DID TRY TO BLEND IN SOME OF THOSE SOLUTIONS AS
WELL...AS NOT COMFORTABLE WITH GOING ALL NAM/SREF AT THIS POINT.
BLENDING IN SOME OF THE GFS/ECMWF DID ALLOW FOR A BIT MORE
SNOW/SLEET AND LESS FREEZING RAIN ACROSS PORTIONS OF NORTHERN PA
INTO SOUTH CENTRAL NY...AND CUT BACK ON SOME OF THE FREEZING RAIN
OVER NORTHERN MAINE. OVERALL IT LOOKS LIKE A WINTRY MIX OF
PRECIPITATION OVER MUCH OF CENTRAL/NORTHERN NEW ENGLAND . SNOW MAY
ONLY BE THE PREDOMINATE TYPE ACROSS PORTIONS OF WESTERN NY ON THE
BACKSIDE OF THE 800-700MB LOW. MUCH OF NEW ENGLAND WILL PROBABLY
END UP SEEING SLEET AS THE PREDOMINATE PTYPE...WITH SOME FREEZING
RAIN AS WELL.

THE MODERATE TO HIGH PROBABILITIES OF 4"+ OF SNOW/SLEET ARE THUS
CONFINED TO MAINLY CENTRAL/WESTERN NY INTO NORTHERN ME. MODERATE
PROBABILITIES OF REACHING 8" ARE GENERALLY CONFINED TO SOUTH
CENTRAL NY ON THE COLDER SIDE OF THE SYSTEM...AND ACROSS FAR
NORTHERN MAINE. GIVEN WARM NOSE ALOFT UNCERTAINTY THERE DOES
REMAIN SOME UNCERTAINTY ON THESE HIGHER AMOUNTS...AND THUS A
SLIGHT CHANCE OF 6"+ DOES EXTEND INTO EASTERN NY AND PORTIONS OF
VT...SO WILL HAVE TO CONTINUE TO MONITOR. A MODERATE TO HIGH
THREAT OF 0.1" OF FREEZING RAIN EXTENDS FROM NORTHERN PA NORTHEAST
INTO MICH OF CENTRAL/NORTHERN NEW ENGLAND. CURRENTLY LOOKS LIKE A
40-70% CHANCE OF A QUARTER INCH OF ICE ACROSS PORTIONS OF EASTERN
MAINE...AND A 10-20% CHANCE OF REACHING 0.5". AGAIN UNCERTAINTY
WITH THE EXACT ICING AMOUNTS IS DEPENDENT ON EXACTLY HOW WARM
ALOFT IT GETS AND THUS WHETHER THE DOMINANT PTYPE IS SLEET OR
FREEZING RAIN. THE NAM WOULD SUGGEST EVEN HIGHER ICING AMOUNTS
WOULD OCCUR....WITH THE GFS/ECWMF NOT AS AGGRESSIVE.

CHENARD

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