Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 240901
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
501 AM EDT MON APR 24 2017

VALID 12Z MON APR 24 2017 - 12Z THU APR 27 2017


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

A SERIES OF SHORTWAVES WILL CONTINUE TO MOVE THROUGH A BROAD UPPER
TROUGH...PRODUCING WIDESPREAD MOUNTAIN SNOW SHOWERS...WITH LOCALLY
HEAVY ACCUMULATIONS...FROM THE CASCADES AND NORTHERN SIERRA TO THE
NORTHERN AND CENTRAL ROCKIES ON MON.  SOME OF THE HEAVIEST
ACCUMULATIONS ARE EXPECTED TO CENTER ALONG THE SOUTHWESTERN
MT...NORTHWESTERN AND CENTRAL WY RANGES.  ENHANCED MID-UPPER LEVEL
LIFT...AFFORDED BY A WELL-DEFINED MID LEVEL SHORTWAVE AND
LEFT-EXIT REGION UPPER JET DYNAMICS...ALONG WITH A LOW LEVEL
CENTER DEVELOPING OVER CENTRAL WY...IS EXPECTED TO RAISE THE
THREAT FOR LOCALLY HEAVY ACCUMULATIONS.  WPC PROBABILISTIC
GUIDANCE INDICATES AT LEAST A SLIGHT RISK FOR 8-INCHES OR MORE
ACROSS MUCH OF THIS REGION ON DAY 1 (ENDING 12 UTC TUE)...WITH A
SLIGHT RISK FOR 12-INCHES ACROSS SOME OF THE HIGHER PEAKS.  THERE
IS ALSO A SIGNIFICANT CHANCE FOR HEAVY SNOWS ALONG PORTIONS OF THE
OREGON ROCKIES ON MON...WHERE FAVORABLE UPPER JET DYNAMICS AND A
STRONG MID LEVEL SHORTWAVE WILL PLAY A ROLE AS WELL.

BY EARLY TUE...AS THE UPPER TROUGH AXIS SHIFTS EAST AND A
SHORTWAVE RIDGE BUILDS...SHOWERS ARE EXPECTED TO BRIEFLY DIMINISH
ACROSS THE NORTHWEST. SNOW SHOWERS WILL CONTINUE FURTHER EAST
HOWEVER ACROSS THE NORTHERN AND CENTRAL ROCKIES...WITH
PROBABILISTIC GUIDANCE CONTINUING TO SHOW THE POTENTIAL FOR
LOCALLY HEAVY AMOUNTS ACROSS SOME OF THE HIGHER PEAKS.

AS SHOWERS WANE ACROSS THE ROCKIES LATE TUE INTO EARLY
WED...PRECIPITATION IS EXPECTED TO RETURN TO THE NORTHWEST AS THE
RIDGE QUICKLY GIVES WAY TO A SHORTWAVE TROUGH ON THE NOSE OF A
POWERFUL JET THAT IS FORECAST TO EXTEND SOUTHEAST FROM EASTERN
PACIFIC ACROSS THE PACIFIC NORTHWEST AND INTO THE GREAT BASIN BY
EARLY THU.  THIS WILL BRING A RENEWED CHANCE FOR LOCALLY HEAVY
SNOW ACCUMULATIONS TO PORTIONS OF THE NORTHERN/CENTRAL CASCADES
AND THE NORTHERN ROCKIES.

THE PROBABILITY OF SIGNIFICANT IS LESS THAN 10 PERCENT.

...NORTHERN PLAINS/UPPER MIDWEST...

LOW TO MID LEVEL FRONTOGENESIS IS EXPECTED TO SUPPORT SOME LIGHT
SNOW ACCUMULATIONS ACROSS NORTHERN ND INTO NORTHWESTERN MN...NORTH
AND WEST OF AN AREA LOW PRESSURE THAT IS FORECAST TO TRACK ACROSS
SD MON BEFORE LIFTING NORTHEAST ACROSS MN MON NIGHT INTO TUE.
OVERALL GUIDANCE CONTINUES TO AGREE THAT THE HEAVIEST
ACCUMULATIONS ASSOCIATED WITH THIS SYSTEM WILL CENTER ACROSS
SOUTHERN MANITOBA INTO WESTERN ONTARIO.  THIS SYSTEM IS EXPECTED
TO 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  NEXT OF THE WESTERN U.S.
SHORTWAVES MOVES OUT INTO THE CENTRAL U.S.  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 INDICATING SEVERAL HOURS OF FREEZING RAIN...RESULTING IN
SIGNIFICANT ICE ACCUMULATIONS 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 IN THE ARROWHEAD
OF DAY 2 (ENDING 12 UTC WED)...SHIFTING SOUTHEAST INTO
NORTHWESTERN WI AND THE WESTERN U.P. ON DAY 3 (ENDING 12 UTC THU).

PEREIRA

$$





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