Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 172120
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
420 PM EST SAT FEB 17 2018

VALID 00Z SUN FEB 18 2018 - 00Z WED FEB 21 2018


DAYS 1-3...

...PACIFIC NORTHWEST TO THE ROCKIES AND NORTHERN HIGH PLAINS...

A DEEP UPPER TROUGH AMPLIFYING OVER THE WESTERN U.S. IS EXPECTED
TO PRODUCE WIDESPREAD SNOWS ACROSS THE NORTHWEST...INCLUDING THE
LOWLANDS OF WESTERN WA AND OREGON...WITH HEAVY ACCUMULATIONS
LIKELY FOR PORTIONS OF THE CASCADES AND THE ROCKIES.

A WELL-DEFINED SHORTWAVE AND ITS DEEP SURFACE CYCLONE WILL
CONTINUE TO DROP SOUTHEAST FROM VANCOUVER ISLAND INTO THE PACIFIC
NORTHWEST SAT NIGHT.  ALTHOUGH THIS SYSTEM IS EXPECTED TO SHEAR
OUT TO THE EAST SUN MORNING...A TRAILING SHORTWAVE WILL CONTINUE
TO DIG SOUTH...FURTHER AMPLIFYING THE FLOW OVER THE NORTHWEST ON
SUN.  BY LATE SUN...THE GFS SHOWS 500MB HEIGHTS DROPPING TO 2-3
STANDARD DEVIATIONS BELOW NORMAL ACROSS MUCH OF THE
NORTHWEST...GREAT BASIN AND THE NORTHERN ROCKIES.  THIS WILL BRING
SNOW LEVELS INTO THE LOWLANDS OF WESTERN WA AND OREGON.
ACCUMULATING SNOWS ARE LIKELY ALONG THE COASTAL RANGES OF
WA...OREGON AND NORTHWEST CA.  HEAVY ACCUMULATIONS ARE LIKELY FOR
PORTIONS OF THE NORTHERN CASCADES AND NORTHERN ROCKIES...FROM
NORTHERN ID AND WESTERN MT TO WESTERN WY AND NORTHERN UT...WITH
WPC DAY 1 PROBABILITIES (ENDING 00 UTC MON) SHOWING THE WIDESPREAD
POTENTIAL FOR ACCUMULATIONS OF 12-INCHES OR MORE.

MODELS SHOW THE TROUGH CONTINUING TO AMPLIFY AND SHIFT EAST ACROSS
THE WESTERN U.S. AS A STRONG SHORTWAVE DIGS SOUTHEAST ACROSS CA
INTO THE GREAT BASIN.  AT THE SURFACE...A DEEP SURFACE CYCLONE IS
FORECAST TO MOVE FROM EASTERN UT INTO WESTERN CO.  DEEP
SOUTHWESTERLY FLOW AHEAD OF THE TROUGH ALONG WITH FAVORABLE UPPER
JET FORCING IS EXPECTED TO ENCOURAGE HEAVY SNOW ACCUMULATIONS
ALONG THE WASATCH AND WESTERN CO RANGES.  FURTHER TO THE
NORTHEAST...UPSLOPE FLOW IN THE WAKE OF AN ARCTIC BOUNDARY
DROPPING SOUTH...ALONG WITH DEEP FORCING WILL SUPPORT A STRIPE
MODERATE TO LOCALLY HEAVY SNOWS EXTENDING FROM THE SOUTHEAST WY
RANGES NORTHEASTWARD INTO WESTERN SD.

HEAVY SNOW IS EXPECTED TO CONTINUE INTO MON NIGHT AND DEVELOP
ALONG THE EASTERN MOGOLLON INTO SOUTHWEST NM AS THIS AMPLIFIED
UPPER TROUGH CONTINUES TO SHIFT EAST.  ON TUE HOWEVER...MODELS
SHOW PRECIPITATION ENDING ACROSS MUCH OF THE REGION AS THE TROUGH
AXIS BEGINS TO MOVE ACROSS THE FOUR-CORNERS REGION.

...NORTHERN PLAINS TO THE UPPER/MID MS VALLEY AND UPPER GREAT
LAKES...

A SERIES OF SHORTWAVES EJECTING FROM THE WESTERN U.S. TROUGH ARE
EXPECTED TO BRING SEVERAL PERIODS OF WINTRY WEATHER TO THE REGION
OVER THE NEXT FEW DAYS.  THE PREVIOUSLY NOTED SHORTWAVE MOVING
FROM THE PACIFIC NORTHWEST INTO THE NORTHERN PLAINS SAT NIGHT IS
EXPECTED TO PRODUCE A STRIPE OF LIGHT TO MODERATE SNOWS AS IT
MOVES ACROSS THE NORTHERN PLAINS INTO THE UPPER GREAT LAKES REGION
ON SUN.  MODELS CONTINUE TO SHOW THE POTENTIAL FOR SOME LOCALLY
HEAVIER ACCUMULATIONS DEVELOPING ALONG AN AREA OF ENHANCED LOW
LEVEL WARM-ADVECTION AND FRONTOGENESIS SETTING UP ACROSS
NORTHEASTERN MN ON SUN...WITH WPC DAY 1 PROBABILITIES SHOWING A
SLIGHT RISK FOR ACCUMULATIONS OF 8-INCHES OR MORE.

THE NEXT ROUND OF WINTRY WEATHER IS EXPECTED TO DEVELOP A BIT
FURTHER SOUTH AS SOUTHERN STREAM ENERGY CURRENTLY CENTERED OFF OF
NORTHERN BAJA EJECTS THOUGH THE SOUTHWEST INTO THE CENTRAL U.S.
WITH A WEAK SURFACE LOW TRACKING NORTHEAST ACROSS THE MID MS
VALLEY MON AFTERNOON.  MODELS SHOW A STRIPE OF LIGHT TO MODERATE
SNOWS DEVELOPING IN THE WARM ADVECTION PATTERN AHEAD OF THE LOW
AND ALONG A WELL-DEFINED LOW-MID LEVEL BAROCLINIC ZONE THAT IS
FORECAST TO EXTEND EAST-NORTHEAST FROM CENTRAL MN INTO NORTHERN WI
AND THE U.P. OF MI. A WINTRY MIX IS EXPECTED FURTHER TO THE
SOUTH...WITH ACCUMULATING ICE POSSIBLE FROM EASTERN NEB TO
NORTHERN LOWER MI.

AS THE WESTERN TROUGH CONTINUES TO SHIFT EAST ON TUE...MODELS SHOW
A MORE DEFINED SURFACE LOW DEVELOPING ALONG THE RIGHT-ENTRANCE
REGION OF STRENGTHENING UPPER JET AND TRACKING NORTHEAST ACROSS
THE MID MS VALLEY ON TUE.  THIS WILL BEGIN TO DRAW A COPIOUS
AMOUNT OF MOISTURE NORTH INTO THE UPPER MIDWEST...SETTING THE
STAGE FOR A POTENTIALLY SIGNIFICANT ICING EVENT FOR PORTIONS OF
THE MID MS VALLEY TO THE UPPER GREAT LAKES AS THIS WARM MOIST AIR
IS DRAWN ACROSS THE TOP OF A SHALLOW ARCTIC AIRMASS AND FROZEN
GROUND.  WPC DAY 3 PROBABILITIES (ENDING 00 UTC WED) SHOW AT LEAST
A SLIGHT RISK FOR ICE ACCUMULATIONS OF 0.25 INCH OR MORE FROM
EASTERN NEB TO NORTHERN LOWER MI.

...NORTHEAST...

A FAST-MOVING SHORTWAVE CURRENTLY ASSOCIATED WITH WIDESPREAD
PRECIPITATION SPREADING FROM THE OH/TN VALLEYS INTO THE MID
ATLANTIC REGION IS FORECAST TO MOVE QUICKLY FROM THE OH VALLEY
ACROSS THE MID ATLANTIC AND NORTHEAST OVERNIGHT.  SURFACE PRESSURE
DEVELOPING ALONG THE MID-ATLANTIC COAST THIS EVENING IS EXPECTED
TO TRACK EAST-NORTHEASTWARD OVERNIGHT...MOVING SOUTHEAST OF THE
SOUTHERN NEW ENGLAND COAST SUN MORNING.  GUIDANCE CONTINUES TO
SHOW FAVORABLE UPPER JET DYNAMICS AND LOW TO MID LEVEL
FRONTOGENESIS SUPPORTING A STRIPE OF MODERATE PRECIPITATION NORTH
OF THE LOW...WITH SIGNIFICANT SNOW ACCUMULATIONS POSSIBLE ACROSS
PORTIONS OF SOUTHERN NY AND CENTRAL/SOUTHERN NEW ENGLAND.  OVERALL
CONSENSUS OF THE 12 UTC MODELS WAS FOR A SLIGHT SHIFT NORTHWARD
WITH HEAVIER QPF AND SNOW AMOUNTS...RESULTING IN HIGHER
PROBABILITIES FOR HEAVIER ACCUMULATIONS EXTENDING FURTHER NORTH
INTO UPSTATE NY AND CENTRAL NEW ENGLAND.  WPC DAY 1 PROBABILITIES
(ENDING 00 UTC MON) NOW SHOW A MODERATE RISK FOR SNOW
ACCUMULATIONS OF 4-INCHES OR MORE EXTENDING FURTHER NORTH INTO
CENTRAL NEW ENGLAND.  WPC PROBABILITIES ALSO SHOW A SLIGHT RISK
FOR ACCUMULATIONS OF 8-INCHES OR MORE EXTENDING FROM THE LOWER
HUDSON VALLEY INTO SOUTHERN AND CENTRAL NEW ENGLAND.

PEREIRA

$$





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