Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 032108
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
407 PM EST SAT DEC 03 2016

VALID 00Z SUN DEC 04 2016 - 00Z WED DEC 07 2016


DAYS 1-3...

...NORTHWEST/NORTHERN AND CENTRAL ROCKIES/NORTHERN PLAINS...

A COMPLEX UPPER TROUGH OVER THE NORTHERN PACIFIC/ALASKA THIS
MORNING WILL DROP SOUTHEASTWARD AND AMPLIFY AS VERY COLD AIR OVER
ALASKA AND NORTHWEST CANADA BEGINS TO FILTER SOUTHWARD ACROSS
WESTERN CANADA.  THE AMPLIFYING TROUGH...IN CONJUNCTION WITH A
DEVELOPING CUTOFF RIDGE OVER NORTHERN ALASKA WILL SET THE STAGE
FOR A LARGE OUTBREAK OF COLD AIR THAT ULTIMATELY WILL AFFECT THE
US...INITIALLY THE NW US. AS THE TROUGH MOVES SOUTHEASTWARD ACROSS
NORTHWEST US...PACIFIC MOISTURE AND AN INITIAL SURGE OF COLD AIR
WILL PRODUCE HEAVY AMOUNTS OF SNOW ESPECIALLY OVER THE WASHINGTON
AND OREGON CASCADES AND SPREADING EASTWARD ACROSS THE HIGHER
TERRAIN OF THE NORTHWEST AS SNOW LEVELS START TO DROP FROM 2000 TO
4000 FEET TODAY OVER WASHINGTON AND OREGON TO BELOW 1000 FEET BY
SUNDAY TO NEAR SEA LEVEL BY TUESDAY.  AS AN INITIAL IMPULSE MOVES
EASTWARD FROM THE MAIN TROUGH ACROSS THE NORTHWEST ON DAY
1...HEAVIEST SNOW WILL OCCUR ALSO OVER THE MOUNTAINS OF CENTRAL
AND NORTHERN IDAHO/WESTERN MONTANA INTO NORTHWESTERN WYOMING BY
SUNDAY EVENING WHERE THE HIGHEST ELEVATIONS WERE LIKELY TO HAVE AT
LEAST 6 TO 12 INCHES WITH ACCUMULATIONS EXPECTED TO EXCEED A FOOT
IN SOME OF THESE LOCATIONS.

AS THIS INITIAL IMPULSE PUSHES EASTWARD ACROSS THE NORTHWESTERN
CORNER OF THE NATION...INCLUDING THE NORTHERN
ROCKIES...SIGNIFICANT SNOW MOVES FARTHER SOUTH AND EASTWARD
BRINGING SNOW INTO NORTHERN NEVADA/THE WASATCH AND UNINTA IN UTAH
AND INTO THE NORTHERN COLORADO ROCKIES.  HEAVIEST SNOW IS EXPECTED
TO CONTINUE ACROSS THE MOUNTAINS OF NORTHERN AND WESTERN WYOMING
WITH AN ADDITION 6 TO 10 INCHES MOST LIKELY WHILE SNOW WILL ALSO
CONTINUE ALONG PORTIONS OF THE CASCADES AND INTO THE LOWER COASTAL
RANGES OF WASHINGTON AND OREGON AS SNOW LEVELS CONTINUE TO DROP.
ADDITIONAL ACCUMULATIONS OF GREATER THAN 4 INCHES ARE POSSIBLE IN
PORTIONS OF THE CENTRAL IDAHO MOUNTAINS/THE UINTA IN UTAH AND MUCH
OF WESTERN AND NORTHERN COLORADO INTO PORTIONS OF WESTERN MONTANA.

AS THIS SHORTWAVE SYSTEM LIFTS NORTHEASTWARD...MODEL DIFFERENCES
ARE SIGNIFICANT ON DAY 2/SUNDAY EVENING INTO MONDAY AS SNOW IS
EXPECTED TO STREAK NORTHEAST ACROSS EASTERN MONTANA INTO NORTH
DAKOTA.  WHILE SOME MODELS GIVE SIGNIFICANT SNOW POSSIBLY GREATER
THAN 4 INCHES...ENSEMBLE PROBABILITIES REMAIN AT 30 PERCENT OR
LOWER FOR GREATER THAN 4 INCHES OF SNOW DUE TO THE LARGE
VARIABILITY IN SOLUTIONS.  THERE SEEMS TO BE MORE PREDICTABLE
SNOWFALL IN NORTHERN NORTH DAKOTA INTO ADJACENT MANITOBA ON DAY 3/
MONDAY EVENING INTO TUESDAY AS THE SHORTWAVE APPEARS TO
CONSOLIDATE AND GENERATE A SURFACE LOW ALONG THE LEADING EDGE OF
THE COLD FRONT.  AT THIS POINT...SOME OF THE VERY COLD AIR FROM
NORTHWESTERN CANADA WILL BE MAKING AN APPEARANCE ACROSS THE
NORTHERN ROCKIES INTO THE NORTHERN PLAINS. WHILE SNOWFALL
EXCEEDING 4 INCHES OF SNOW IS EXPECTED TO FALL ALONG THE BORDER OF
NORTH DAKOTA/NW MINNESOTA NORTHWARD...HEAVIEST SNOW IS LIKELY TO
FALL ACROSS MANITOBA.

AS THE REMAINING SHORTWAVE ENERGY MOVES SOUTHEASTWARD ACROSS THE
NORTHWEST...SNOW LEVELS WILL FALL ACROSS WASHINGTON AND
OREGON...ALLOWING SNOW TO FALL CLOSER TO THE COAST ALTHOUGH ONLY
LIGHT AMOUNTS ARE EXPECTED EXCEPT OVER WESTERN OREGON...WHERE THE
SOUTHERN CASCADES AND SOME OF THE COASTAL RANGES OF SOUTHWESTERN
OREGON INTO EXTREME NORTHWESTERN CALIFORNIA HAVE A LOW TO MODERATE
PROBABILITY OF 4 INCHES OF SNOW OR MORE.

...MIDWEST/NORTHEAST/MIDDLE ATLANTIC...

A NEGATIVELY TILTED ALBEIT WEAKENING UPPER TROUGH MOVES FROM THE
MIDWEST TOWARD THE NORTHEAST US ON SUNDAY AND MONDAY.  THIS SYSTEM
APPEARS TO SHEAR OUT SUBSTANTIALLY AS IT APPROACHES AND INTERACTS
WITH A SHORTWAVE UPPER RIDGE.  WHILE THIS SYSTEM APPEARS TO OUTRUN
A SIGNIFICANT UPPER LOW OVER NORTHWESTERN MEXICO...IT APPEARS TO
TAP INTO MOISTURE FROM THE LARGE RAINMAKING SYSTEM OVER THE GULF
COAST STATES. AS A RESULT...WET SNOW IS LIKELY AS LIFT AHEAD OF
THE TROUGH PRODUCES SOME OF THE FIRST SIGNIFICANT SNOW OF THE
SEASON FOR PARTS OF THE MIDWEST...INCLUDING CHICAGO/MILWAUKEE AND
PORTIONS OF IOWA/SOUTHEAST MINNESOTA AND WISCONSIN.  THERE IS A
LOW TO MODERATE...20 TO 60 PERCENT CHANCE OF GREATER THAN 4 INCHES
OF SNOW ACROSS EASTERN IOWA INTO NORTHWESTERN ILLINOIS AND
SOUTHERN WISCONSIN WHILE LIGHTER AMOUNTS ARE PROBABLE ELSEWHERE.
AS THE SYSTEM HEADS EAST AND WEAKENS ON MONDAY...MOSTLY LIGHT SNOW
WILL FALL ACROSS MICHIGAN/NORTHERN PENNSYLVANIA/INTERIOR NEW YORK.

AS THE SOUTHERN CUTOFF SYSTEM MOVES EAST AND NORTHEASTWARD ON
TUESDAY...RAIN WILL SPREAD NORTHEASTWARD WHILE MARGINALLY COLD AIR
WILL REMAIN OVER THE INTERIOR PORTIONS OF THE MIDDLE ATLANTIC
STATES AND NORTHERN APPALACHIANS...WHERE PRECIPITATION COULD START
OF CHANGE OVER TO SNOW AND POSSIBLY SOME FREEZING RAIN FROM
WESTERN VIRGINIA/WEST VIRGINIA/WESTERN MARYLAND INTO SOUTHWEST
PENNSYLVANIA AND NEW ENGLAND.  THE PRECIPITATION WILL STILL LIKELY
BE FALLING BY THE END OF THE FORECAST PERIOD DAY 3/TUESDAY BUT
PROBABILITIES FOR 4 INCHES OF SNOW FOR GREATER WILL LIKELY BE LESS
THAN 10 PERCENT.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

KOCIN

$$




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