Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 250836
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
435 AM EDT TUE APR 25 2017

VALID 12Z TUE APR 25 2017 - 12Z FRI APR 28 2017


...PACIFIC NORTHWEST TO THE NORTHERN AND CENTRAL ROCKIES...

A SERIES OF SHORTWAVES MOVING THROUGH A BROAD UPPER TROUGH
CENTERING OVER THE WESTERN U.S. WILL CONTINUE TO SUPPORT PERIODS
OF SNOW IN THE MOUNTAINS...WITH LOCALLY HEAVY ACCUMULATIONS
POSSIBLE ACROSS PARTS OF THE HIGH TERRAIN.

EARLY IN THE PERIOD...MODELS A SHOW A WELL-DEFINED MID-UPPER LEVEL
SHORTWAVE MOVING EAST ACROSS WY INTO THE NORTHERN PLAINS...WITH A
DEVELOPING LOW LEVEL LOW DROPPING EAST-SOUTHEAST ACROSS EASTERN WY
ON TUE.  THIS WILL SUPPORT HEAVY SNOWS ACROSS THE BIGHORNS WITH
LIGHTER ACCUMULATIONS SPREADING EAST INTO THE BLACK HILLS AND THE
ADJACENT HIGH PLAINS ON TUE.  MEANWHILE...ANOTHER ROBUST SHORTWAVE
IS FORECAST TO DIVE FURTHER SOUTH THROUGH THE GREAT BASIN INTO THE
SOUTHWEST AND SOUTHERN ROCKIES.  FAVORABLE UPPER FORCING TO THE
NORTH IS FORECAST TO HELP PRODUCE SOME MODERATE TO LOCALLY HEAVY
ACCUMULATIONS ACROSS THE CO RANGES. STRONG POST-FRONTAL
NORTHEASTERLY FLOW IS EXPECTED TO HELP BOLSTER AMOUNTS ALONG THE
SANGRE DE CRISTOS WHERE WPC PROBABILISTIC GUIDANCE SHOWS A
MODERATE RISK FOR LOCAL ACCUMULATIONS OF 8-INCHES OR GREATER ON
DAY 1 (ENDING 12 UTC WED).

BACK TO THE NORTHWEST...A SHORTWAVE RIDGE IS FORECAST TO PROVIDE
BRIEF PAUSE IN THE WET WEATHER ON TUE BEFORE GIVING WAY TO A
SHORTWAVE TROUGH POSITIONED ON THE LEADING EDGE OF A POWERFUL
UPPER JET MOVING INTO THE NORTHWESTERN U.S. EARLY WED.  THIS WILL
BRING THE RETURN OF SNOW SHOWERS TO THE CASCADES AND THEN THE
NORTHERN ROCKIES ON WED...WITH WPC PROBABILISTIC GUIDANCE
INDICATING A SLIGHT THREAT FOR LOCALLY HEAVY ACCUMULATIONS ACROSS
PORTIONS OF THE NORTHERN CASCADES...THE CENTRAL ID...SOUTHWESTERN
MT AND WESTERN WY RANGES ON DAY 2 (ENDING 12 UTC THU).

BY DAY 3 (12 UTC THU - 12 UTC FRI)...THE HEAVY SNOW THREAT IS
FORECAST TO SHIFT FURTHER SOUTH AND EAST...WITH THE HEAVY SNOW
THREAT RETURNING TO PORTIONS OF THE CENTRAL WY AND CO RANGES.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

...UPPER MIDWEST/GREAT LAKES...

THE SYSTEM CURRENTLY IMPACTING NORTHWESTERN MN...NORTHERN WI AND
THE U.P. OF MI IS EXPECTED TO WEAKEN AND SHEAR INTO WESTERN
ONTARIO ON TUE.  HOWEVER...LOW PRESSURE AND
HEAVIER PRECIPITATION IS EXPECTED TO DEVELOP AND LIFT NORTHEAST
ALONG ITS TRAILING BOUNDARY AS THE PREVIOUSLY NOTED WAVE MOVING
INTO THE NORTHERN PLAINS MOVES FURTHER EAST AND BEGINS TO PHASE
WITH THE SOUTHERN WAVE LIFTING NORTH OUT OF THE SOUTHERN ROCKIES
BY EARLY WED.  LOW LEVEL COLD AIR SUPPORTED BY A STRONG LOW LEVEL
RIDGE EXTENDING SOUTH FROM CENTRAL CANADA IS EXPECTED TO REMAIN IN
PLACE...PRODUCING MIXED PRECIPITATION NORTH OF THE ASSOCIATED
LOW...WITH SEVERAL GUIDANCE MEMBERS CONTINUING TO INDICATE A
PERIOD OF FREEZING RAIN...WITH SIGNIFICANT ICE ACCUMULATIONS
POSSIBLE FROM THE ARROWHEAD REGION OF MN TO THE WESTERN U.P. OF
MI.  WPC PROBABILISTIC GUIDANCE SHOWS A SLIGHT RISK FOR ICE
ACCUMULATIONS OF A 0.25 INCH OR MORE ACROSS PORTIONS OF THE
ARROWHEAD ON DAY 1 (ENDING 12 UTC WED)...SHIFTING SOUTHEAST TO
INCLUDE PARTS NORTHWESTERN WI AND THE WESTERN U.P. ON DAY 2
(ENDING 12 UTC THU).

PEREIRA

$$





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