Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 192009
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
308 PM EST SUN NOV 19 2017

VALID 00Z MON NOV 20 2017 - 00Z THU NOV 23 2017


DAYS 1-3...

...GREAT LAKES...

AN INITIAL PERIOD OF COLD AIR ADVECTION ACROSS LAKES HURON AND
ERIE/ONTARIO AND LEE AREA LOW LEVEL CONVERGENCE LEADS TO
PERSISTENCE OF THE LAKE EFFECT SNOW SHOWERS THIS EVENING.  THE
HEAVIEST SNOWS ARE EXPECTED TO OCCUR NEAR THE SOUTHEAST CORNER OF
LAKE ONTARIO...WITH THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION.  THE UNCERTAINTY LIES WITH BAND EVOLUTION AND
CHANGING WIND PROFILES THAT LEADS TO THE BAND(S) CHANGING
LOCATION. THE 12Z MODEL RUNS SHOW WINDS BACKING WITH TIME...SO THE
LOCATION OF BANDS SHOULD SHIFT NORTH OVERNIGHT AND MONDAY MORNING
OFF OF BOTH LAKES ERIE AND ONTARIO.  THE BANDS OFF THE SOUTHEAST
CORNER OF LK ONTARIO TONIGHT SHOULD SHIFT TO EAST OF THE LAKE MON.
 THE CHANGING LOCATION LEADS TO A LOW PROBABILITY OF A LONGER
DURATION HEAVY SNOW SNOW EVENT IN ANY ONE LOCATION.

...PACIFIC NORTHWEST/NORTHERN ROCKIES...

A VIGOROUS FRONT AND ASSOCIATED UPPER DIVERGENCE MAXIMA IN THE
COUPLED REGION OF THE JET WILL BRING HEAVY MOUNTAIN SNOWS TO THE
NORTHERN WA CASCADES SUN EVENING. WPC DAY 1 PROBABILITIES CONTINUE
TO INDICATE A SIGNIFICANT THREAT FOR ACCUMULATIONS OF A FOOT OR
MORE OVER THE HIGHER REACHES OF THE NORTHERN WASHINGTON CASCADES.

THE JET EXTENDS FURTHER INLAND INTO THE NORTHERN ROCKIES...WITH A
SECOND AREA OF HEAVY SNOW IN THE RANGES OF CENTRAL TO NORTHERN ID
AND NORTHWEST MT.  A BREAK DEVELOPS IN THE CASCADES AS DRIER AIR
ALOFT ADVECTS INTO THE REGION MONDAY.

THIS SYSTEM IS EXPECTED TO WEAKEN AND DEPART FOR THE PLAINS
MONDAY. AN UPPER JET MAXIMA EXTENDS EAST FROM OR AND ID INTO
NORTHWEST WY.  ON DAY 2 THE PRIMARY FOCUS IS WHERE UPPER
DIVERGENCE MAXIM IN THE UPPER JET CROSS OVER THE RANGES OF
NORTHWEST WY...WHERE LIGHT SNOW ARE EXPECTED MON NIGHT-EARLY TUE.
SNOW LEVELS WILL BE ON THE INCREASE AS A STRONG RIDGE CONTINUES TO
BUILD ACROSS THE WESTERN U.S.

ON DAY 3 (TUE NIGHT-WED)...WPC PROBABILITIES SHOW LITTLE POTENTIAL
FOR HEAVY SNOW ACROSS THE U.S. A FEW ENSEMBLE MEMBERS SHOW A
CONTINUATION OF LIGHT SNOW SHOWERS IN THE RANGES OF NORTHWEST WY.
MOST MODELS/ENSEMBLE MEANS DO NOT SHOW ANYTHING BEYOND A SPOTTY
INCH OR TWO.

FOR DAYS 1-3...THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN
10 PERCENT.

PETERSEN


$$




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