Quantitative Precipitation Forecast
Issued by NWS

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305
FOUS11 KWBC 232004
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
404 PM EDT SAT APR 23 2016

VALID 00Z SUN APR 24 2016 - 00Z WED APR 27 2016


DAYS 1-3...

...CENTRAL GREAT BASIN TO THE CENTRAL AND NORTHERN ROCKIES/HIGH
PLAINS...

SNOWFALL WILL OCCUR THE CENTRAL GREAT BASIN TO THE NORTHERN
ROCKIES THIS WEEKEND AND INTO EARLY NEXT WEEK.  SATURDAY NIGHT
INTO SUNDAY...THE HEAVIEST SNOW WILL FOCUS ALONG THE RANGES OF
NORTHWEST WYOMING PLUS THE RANGES OF SOUTHWEST MONTANA AND
BIGHORNS WHILE THE INITIAL 700 MB LOW CROSSES WYOMING INTO SD.
MOIST LOW LEVEL-FLOW INTO THE TERRAIN INCREASES TO THE NORTH OF A
SURFACE LOW DEEPENING IN THE LEE OF THE NORTHERN ROCKIES. THE DAY
1 HIGHEST TOTALS ARE FORECAST OVER THE BIGHORNS DUE TO BOTH
DURATION AND A PERSISTENT UPPER DIVERGENCE MAXIMA TONIGHT INTO
EARLY SUN. A SECONDARY MAX ON DAY 2 IS POSSIBLE ALONG THE TRAILING
LOW LEVEL FRONT AND DEFORMATION ZONE IN NORTHEAST MT...WHERE THE
09Z SREF MEAN/00Z ECMWF/06Z NAM SHOW POTENTIAL FOR SEVERAL INCHES
OF SNOW.

ON SUNDAY NIGHT...AN UPPER TROUGH AMPLIFYING OVER THE WESTERN U.S.
DRIFTS EAST WITH THE MODEL MAJORITY SHOWING A CLOSED 700 MB LOW
FORMING IN NORTHEAST NV BY 12Z MON.
LOWERING TEMPERATURES COMBINED WITH STRONG LOW-MID LEVEL FORCING
SHOULD LEAD TO PERIODS OF HEAVY SNOW ACROSS NORTHEAST NEVADA ON
MONDAY...SPREADING SLOWLY NORTHEAST INTO HIGHER ELEVATIONS OF
SOUTHERN ID AND WYOMING AS THE UPPER LOW EDGES EAST NORTHEAST MON
NIGHT AND TUE.

MODELS WERE GENERALLY IN GOOD AGREEMENT WITH THE LARGE SCALE
EVOLUTION OF FLOW OVER THE WESTERN U.S....WITH MINOR TIMING/TROUGH
AMPLITUDE DIFFERENCES THAT DEVELOP WITH THE SECOND LOW CLOSING OFF
OVER THE GREAT BASIN/CO/WY.  A CONSENSUS APPROACH WAS TAKEN
WITHOUT WEIGHTING ONE SOLUTION MORE THAN OTHERS.
THE 12Z ECMWF FORECASTS MORE SNOW ON THE 12Z RUN IN EASTERN WY ON
DAY 3 AS IT STRENGTHENS THE HIGH PLAINS LEE CYCLONE FASTER THAN ON
THE 00Z RUN...RESULTING IN GREATER PRECIP WRAPPING AROUND THE LOW
INTO THE TROWAL REGION NORTHWEST OF THE CIRCULATION...WHICH IS
COLDER IN SOUTHEAST WY TUE AFTERNOON IN RESPONSE TO THE STRONGER
CIRCULATION.

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

PETERSEN

$$





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