Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 230912
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
511 AM EDT SUN APR 23 2017

VALID 12Z SUN APR 23 2017 - 12Z WED APR 26 2017


...PACIFIC NORTHWEST/NORTHERN AND CENTRAL ROCKIES...

SHOWERS ARE FORECAST BECOME MORE NUMEROUS ACROSS THE REGION BY
EARLY SUN AS A SHORTWAVE RIDGE GIVES WAY TO A SERIES OF
PROGRESSIVE SHORTWAVE TROUGHS THAT ARE EXPECTED TO CARVE OUT A
BROAD UPPER TROUGH THAT WILL EXTEND ACROSS THE WESTERN U.S.
EXPECT SNOW SHOWERS TO DEVELOP ALONG THE NORTHERN TO CENTRAL
CASCADES AND PORTIONS OF THE NORTHERN ROCKIES FROM CENTRAL ID TO
NORTHWESTERN WY ON SUN.  BUT WITH SNOW LEVELS EXPECTED TO BE
FAIRLY HIGH...WIDESPREAD HEAVY ACCUMULATIONS ARE NOT EXPECTED
THROUGH EARLY MON.

SHOWERS ARE EXPECTED TO CONTINUE ACROSS PACIFIC NORTHWEST AND
NORTHERN ROCKIES INTO EARLY TUE WHILE EXTENDING SOUTH INTO THE
CENTRAL ROCKIES WITH THE ARRIVAL OF A SECOND...MORE ROBUST
SHORTWAVE.  AMPLE MOISTURE AND LOWER SNOW LEVELS ARE EXPECTED TO
RAISE THE POTENTIAL FOR HEAVIER SNOW ACCUMULATIONS ACROSS PORTIONS
OF THE CASCADES AND NORTHERN ROCKIES.  A MID LEVEL WAVE DEVELOPING
OVER WY MON NIGHT IS EXPECTED TO HELP ACCENTUATE THE LOW LEVEL
INFLOW/UPSLOPE FLOW INTO THE SOUTHWESTERN MT...NORTHWESTERN  AND
CENTRAL WY RANGES...RAISING THE THREAT FOR LOCALLY HIGH ELEVATION
SNOWS THERE AS WELL TUE NIGHT INTO WED.

ON TUE MODELS SHOW THE TROUGH BEGINNING TO AMPLIFY AND SHIFT EAST
INTO THE PLAINS...WITH SHOWERS DIMINISHING FROM NORTH TO SOUTH
ACROSS MUCH OF WY INTO CO BY EARLY WED.   FURTHER NORTHWEST...SNOW
SHOWERS ARE EXPECTED TO CONTINUE ACROSS THE MOUNTAINS AS A SERIES
OF SHORTWAVES EMBEDDED WITHING BROADLY DIFFLUENT ALOFT CONTINUE TO
INFLUENCE THE REGION.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

...NORTHERN NORTH DAKOTA/MINNESOTA...

THE COLD FRONT CURRENTLY SAGGING SOUTH ACROSS THE UPPER MIDWEST
AND NORTHERN PLAINS IS EXPECTED TO LINGER ACROSS THE REGION INTO
EARLY MON...BEFORE LIFTING BACK TO THE NORTH AHEAD OF A DEVELOPING
LOW ASSOCIATED WITH ONE OF THE PREVIOUSLY NOTED SHORTWAVES MOVING
ACROSS THE WEST.  SOME LIGHT SNOW ACCUMULATIONS ARE POSSIBLE
ACROSS FAR NORTHERN MN BEFORE PRECIPITATION LIKELY CHANGES OVER TO
RAIN ON MON.  SOME LIGHT SNOW ACCUMULATIONS ARE ALSO POSSIBLE ON
THE BACKSIDE OF THE SYSTEM OVER NORTHERN ND...BUT OVERALL THE
GREATEST THREAT FOR ANY SIGNIFICANT ACCUMULATIONS IS EXPECTED TO
CENTER TO THE NORTH ACROSS SOUTHERN MANITOBA AND WESTERN ONTARIO.
THIS SYSTEM IS EXPECTED TO WEAKEN AS IT LIFTS INTO WESTERN ONTARIO
ON TUE.  HOWEVER...LOW PRESSURE AND HEAVIER PRECIPITATION IS
EXPECTED TO DEVELOP AND LIFT NORTHEAST ALONG THE BOUNDARY AS THE
NEXT OF THE WESTERN U.S. SHORTWAVES MOVES OUT INTO THE CENTRAL
U.S.  STRONG SURFACE HIGH PRESSURE SUPPORTED BY CONFLUENT FLOW
ALOFT IS FORECAST TO CENTER OVER CENTRAL CANADA WED MORNING.
STRONG NORTHEASTERLY WINDS BETWEEN THE HIGH AND THE LOW LIFTING UP
FROM THE SOUTH WILL DRAW MUCH COLDER AIR FROM CANADA DOWN ACROSS
THE UPPER MIDWEST.  THIS WILL SET THE STAGE FOR A MIXED
PRECIPITATION EVENT ALONG THE WESTERN SHORES OF LAKE SUPERIOR WED
MORNING.  WHILE ACCUMULATING SNOWS ARE POSSIBLE ACROSS NORTHWEST
MN...SEVERAL OF THE 00 UTC MODELS RUNS SHOW A PERIOD OF FREEZING
RAIN WITH SIGNIFICANT ICE ACCUMULATIONS FURTHER TO THE EAST ACROSS
NORTHWESTERN WI INTO THE WESTERN U.P. OF MI.

PEREIRA





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