Quantitative Precipitation Forecast
Issued by NWS

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661
FOUS11 KWBC 232017
QPFHSD

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

VALID 00Z MON APR 24 2017 - 00Z THU APR 27 2017


...PACIFIC NORTHWEST/NORTHERN AND CENTRAL ROCKIES/ADJACENT HIGH
PLAINS...

A SERIES OF PROGRESSIVE SHORTWAVE TROUGHS ARE EXPECTED TO CARVE
OUT A BROAD UPPER TROUGH ACROSS THE WESTERN U.S. OVER THE NEXT FEW
DAYS. ONE SHORTWAVE WILL QUICKLY CROSS THE ROCKIES TONIGHT,
BRINGING RELATIVELY LIGHT SNOW ACCUMULATIONS TO PORTIONS OF THE
NORTHERN INTERMOUNTAIN REGION ND NORTHERN ROCKIES, WHERE WPC DAY 1
(00Z MON-00Z TUE) PROBABILITIES SHOW A SLIGHT TO MODERATE RISK OF
EXCEEDING 4 INCHES OF SNOW. DURING THE DAY ON MON A SECOND,
STRONGER SHORTWAVE WILL MOVE ONSHORE IN THE PAC NW. THIS WAVE IS
EXPECTED TO HAVE THE STRONGEST HEIGHT FALLS ASSOCIATED WITH IT AS
IT MOVES INLAND, CARVING OUT THE BROAD UPPER TROUGH AS IT MOVES
INTO THE ROCKIES ON DAY 2 (00Z TUE-00Z WED). THIS SYSTEM WILL
PRODUCE SNOWS ACROSS THE CASCADES ON DAY 1, WITH WPC PROBABILITIES
SHOWING A SLIGHT TO MODERATE RISK OF EXCEEDING 4 INCHES, AND A
SLIGHT RISK OF EXCEEDING 8 INCHES ACROSS THE OR CASCADES. AS THIS
WAVE MOVES INLAND ON DAY 2 AND HEIGHTS ALONG WITH SNOW-LEVELS
FALL, MODERATE TO HEAVY SNOWS ARE EXPECTED TO DEVELOP FOR PORTIONS
OF THE NORTHERN AND CENTRAL ROCKIES. WPC DAY 2 PROBABILITIES SHOW
A MODERATE TO HIGH RISK OF EXCEEDING 4 INCHES ACROSS MUCH OF THE
CENTRAL/NORTHERN ROCKIES, WITH A SLIGHT TO MODERATE RISK OF
EXCEEDING 8 INCHES. A SLIGHT TO MODERATE RISK OF EXCEEDING 12
INCHES IS ALSO SHOWN AT THE HIGHEST ELEVATIONS OF THE BIG HORNS
AND SOUTHERN PORTIONS OF THE ABSAROKA RANGE. ADDITIONALLY ON DAY
2, RAIN MAY MIX WITH OR CHANGE TO SNOW ACROSS THE BLACK HILLS AND
PERHAPS SOME OF THE SURROUNDING AREAS. SLIGHT TO MODERATE
PROBABILITIES OF EXCEEDING 4 INCHES ARE SHOWN FOR THESE AREAS ON
DAY 2, WITH A SLIGHT RISK OF EXCEEDING 8 INCHES FOR THE BLACK
HILLS.

SNOWS ARE EXPECTED TO CONTINUE ACROSS MUCH OF THE ROCKIES ON DAY 3
(00Z WED-00Z THU) AS ANOTHER SHORTWAVE MOVES INTO THE
NORTHWEST/NORTHERN INTERMOUNTAIN REGION. A SLIGHT TO MODERATE RISK
OF EXCEEDING 4 INCHES IS SHOWN ON DAY 3 FOR THE CASCADES AS WELL
AS PORTIONS OF THE NORTHERN/CENTRAL ROCKIES, WITH A SLIGHT RISK
FOR 8 INCHES ACROSS THE TETONS, THE ABSAROKAS, AND THE WIND RIVER
MOUNTAINS. MULTI-DAY SNOWFALL TOTALS COULD EXCEED 2 FEET ACROSS
SOME OF THESE AREAS.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

...UPPER MIDWEST...

THE COLD FRONTAL BOUNDARY ACROSS THE UPPER MIDWEST AND NORTHERN
PLAINS TODAY 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. A PERIOD OF FREEZING DRIZZLE OR LIGHT FREEZING
RAIN IS POSSIBLE TONIGHT FROM PORTIONS OF ND INTO NORTHERN MN
BEFORE PRECIPITATION CHANGES TO SNOW OR SLEET. SOME 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. A SLIGHT TO MODERATE RISK OF EXCEEDING 4 INCHES IS
SHOWN FOR THESE AREAS ON THE DAY 1 WPC PROBABILITIES. OVERALL THE
GREATEST THREAT FOR ANY SIGNIFICANT ACCUMULATIONS IS EXPECTED TO
CENTER TO THE NORTH ACROSS SOUTHERN MANITOBA AND WESTERN ONTARIO.
AN ADDITIONAL AREA OF LOW PRESSURE AND HEAVIER PRECIPITATION IS
EXPECTED TO DEVELOP AND LIFT NORTHEAST ALONG THE FRONT AS THE NEXT
OF THE WESTERN U.S. SHORTWAVES MOVES OUT INTO THE CENTRAL U.S.
LATE TUE INTO TUE NIGHT/WED. 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 ACROSS THE UPPER GREAT
LAKES. WHILE ACCUMULATING SNOWS ARE POSSIBLE ACROSS NORTHEASTERN
MN (AS SHOWN BY A SLIGHT RISK FOR EXCEEDING 4 INCHES ON WPC DAY 3
SNOW PROBABILITIES), SEVERAL OF THE 12Z MODEL RUNS SHOW A PERIOD
OF FREEZING RAIN WITH THE POTENTIAL FOR SIGNIFICANT ICE
ACCUMULATIONS FROM NORTHEASTERN MN EAST ACROSS NORTHERN WI AND
WESTERN PORTIONS OF THE MICHIGAN UPPER PENINSULA. MUCH UNCERTAINTY
REMAINS AS TO THE DEGREE OF SNOW/FREEZING RAIN, AS MODELS CONTINUE
TO SHOW DIFFERENCES WITH RESPECT TO THE SURFACE LOW TRACK TUE
NIGHT/WED FROM THE MID-MS VALLEY TO THE GREAT LAKES, WHICH IN TURN
IMPACTS THE EXTENT OF THE POTENTIAL WARM LAYER ABOVE THE SURFACE
AS WELL AS THE AMOUNT OF PRECIP THAT FALLS. WPC FREEZING RAIN
PROBABILITIES THIS FORECAST CYCLE FOR DAY 3 SHOW A SLIGHT TO
MODERATE RISK OF 0.10 INCH OF FREEZING RAIN FROM NORTHEASTERN MN
ACROSS NRN WI AND THE WRN U.P. OF MICHIGAN, WITH A SLIGHT RISK OF
0.25 INCH FOR SOME OF THE SAME AREAS.

RYAN

$$





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