Quantitative Precipitation Forecast
Issued by NWS

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471
FOUS11 KWBC 230819
QPFHSD

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

VALID 12Z MON JAN 23 2017 - 12Z THU JAN 26 2017

DAYS 1-3...

...RANGES FROM CA TO THE GREAT BASIN AND CENTRAL/SOUTHERN
ROCKIES...

THE MODELS INDICATE THE PLUME OF ENHANCED MOISTURE AND VERTICAL
MOTION SHIFTS INLAND IN CONCERT WITH THE UPPER LEVEL JET MAXIMA
FROM CALIFORNIA ACROSS THE GREAT BASIN WITH 700 MB VERTICAL MOTION
AND RELATIVE HUMIDITY MAXIMA CROSSING INTO THE RANGES OF WESTERN
WY AND NORTHERN UT AND THEN INTO WESTERN CO...WITH A SECONDARY
MAXIMA IN THE MOGOLLON RIM IN AZ.
AS THE 700 MB WAVE DEPARTS FOR THE PLAINS ON TUE...THE STRENGTH OF
ASCENT AND RESULTANT PRECIPITATION WANES ACROSS THE CENTRAL AND
SOUTHERN ROCKIES...WITH LIGHT ADDITIONAL SNOW WHERE HIGH RELATIVE
HUMIDITY PERSISTS IN THE RANGES OF SOUTHEAST WY AND CO AS THE
UPPER TROUGH DRIFTS SLOWLY EAST ACROSS THE REGION.  A FOOT OR MORE
OF SNOW WILL BE POSSIBLE ACROSS PARTS OF THE UT WASATCH/WY TETONS
AND CO ROCKIES.

CA FINALLY GETS A BREAK ON DAY 2 AS THE UPPER TROUGH MOVES AWAY
FROM THE STATE AND THE MID-UPPER RIDGE APPROACHES FROM THE EASTERN
PACIFIC.  THE MODELS SHOWS A 700 MB WAVE APPROACHING ON DAY 3.
DOWNSTREAM FROM THE WAVE MODEST WARM/MOIST ADVECTION OCCURS AND A
PERIOD OF SNOW IS POSSIBLE IN THE RANGES OF NORTHWEST CA. WITH THE
APPROACHING 700 MB WAVE DEAMPLIFYING WITH TIME...THE POTENTIAL FOR
HEAVY SNOW IS LIMITED.

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

ON MON THE 700 MB WAVE CROSSES WY AND ADJACENT NORTHERN CO AND
THEN CLOSES OFF INTO A LOW THAT CROSSES NEAR THE SD/NE BORDER BY
TUE MORNING  AND THEN TURNS EAST NORTHEAST TO THE UPPER MS VALLEY
SOMEWHERE NEAR THE WI/IA BORDER BY WED MORNING.  THE MODELS FCST A
WELL DEFINED SWATH OF WARM/MOISTURE ADVECTION IN ADVANCE OF THE
CIRCULATION AND THEN CONVERGENCE MAXIMA AS THE CIRCULATION CROSSES
ALONG THE LOW TRACK.  A PRECIP MAXIMA IS FORECAST ALONG THIS PATH
AND ALSO EXTENDING A FEW COUNTIES FURTHER NORTH INTO THE LOW LEVEL
JET AXIS.
THE MODELS ARE IN BETTER THAN AVERAGE AGREEMENT ON THE LOW TRACK
DAY 2 WITH SPREAD GROWING ON DAY 3 AS THE NAM/21Z SREF MEAN EXTEND
THE CIRCULATION A LITTLE FASTER AND FURTHER NORTH  THAN THE
UKMET/ECMWF. WPC FOLLOWED A CONSENSUS OF THE GEFS MEAN/GFS/ECMWF
AXIS OF ACCUMULATING SNOW FROM WY THROUGH SD/NRN NE INTO THE UPPER
MS VALLEY AND ADJACENT UPPER GREAT LAKES.

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

THE MODELS FORECAST A CYCLONE TO MOVE OFF THE MID ATLANTIC COAST
ON MONDAY WHILE A BLOCKING RIDGE OF HIGH PRESSURE TO THE NORTH
WILL LOCK IN LOW LEVEL COLD AIR OVER NEW ENGLAND.   ATLANTIC AND
GULF MOISTURE ADVECTING INLAND AROUND THE CIRCULATION GETS LIFTED
BY WELL DEFINED UPPER DIVERGENCE/LOWER CONVERGENCE COUPLETS TO
YIELD WIDESPREAD PRECIP ACROSS PA/NJ/NEW YORK AND NEW ENGLAND.

COLD AIR IS INITIALLY LACKING WITH THE 00Z SOUNDINGS AT ALBANY AND
BUFFALO NY WELL ABOVE FREEZING IN THE LOWEST COUPLE HUNDRED MB SO
COOLING IS NEEDED TO PRODUCE SNOW. THE MODELS DO FORECAST A
GRADUAL COOLING TO OCCUR ACROSS NY/NEW ENGLAND...WITH COLD AIR
AROUND THE HIGH ADVECTING ACROSS NORTHERN NEW ENGLAND.  THE COLD
AIR IN CENTRAL AND WESTERN NY AND ADJACENT PA WOULD HAVE TO BE
FROM DYNAMIC COOLING AND THIS IS TRICKY TO PREDICT.

THE THREAT OF SNOW IS GREATER ACROSS HIGHER ELEVATIONS OF WRN AND
NORTHERN NY AND ADJACENT NORTH CENTRAL PA ON DAY 1...AND IN
NORTHERN VT/NH/MAINE ON DAY 2 ADJACENT TO THE ST LAWRENCE VALLEY.
MODELS REMAIN SPLIT ON THE PRECIP TYPE WITH A MIXTURE OF
SNOW/SLEET/FREEZING RAIN LEAVING CONFIDENCE BELOW NORMAL IN
INTERIOR NY/NEW ENGLAND.  BY WED... THE  STORM WILL LIFT UP INTO
THE CANADIAN MARITIMES...WITH SNOW TAPERING ACROSS NORTHERN MAINE.


THE PROBABILITY OF SIGNIFICANT FREEZING RAIN ON DAY 3 IS LESS THAN
10 PERCENT.

PETERSEN

$$





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