Quantitative Precipitation Forecast
Issued by NWS

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073
FOUS11 KWBC 272056
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
456 PM EDT THU APR 27 2017

VALID 00Z FRI APR 28 2017 - 00Z MON MAY 01 2017

...ROCKIES AND ADJACENT HIGH PLAINS...

A MAJOR LATE SEASON SNOW EVENT IS STILL ON TAP FOR THE ROCKIES
OVER THE NEXT FEW DAYS AS AN UPPER TROUGH AMPLIFIES AND CLOSES OFF
OVER THE INTERMOUNTAIN WEST.  THE COMBINATION OF LOW-LEVEL FLOW
INTO THE TERRAIN AND BELOW NORMAL TEMPERATURES WITH THE ANOMALOUS
TROUGH SHOULD SUPPORT PERIODS OF MODERATE TO HEAVY SNOW OVER THE
HIGHER ELEVATIONS OF IDAHO...WESTERN MONTANA...AND ESPECIALLY
WYOMING THURSDAY NIGHT INTO FRIDAY...WITH ACCUMULATING SNOW
POTENTIALLY SPREADING OUT INTO WESTERN NEBRASKA AS THE LEADING
EDGE OF HEIGHT FALLS WITHIN THE AMPLIFYING TROUGH EJECT EASTWARD
INTO THE CENTRAL HIGH PLAINS ON FRIDAY.  WHILE THE UPPER TROUGH
DIGS INTO THE FOUR CORNERS REGION AND WINDS INCREASE AROUND A
SURFACE LOW DEEPENING OVER THE SOUTHERN PLAINS FRIDAY NIGHT INTO
SATURDAY THE FOCUS FOR HEAVY SNOW WILL SHIFT SOUTHWARD INTO THE
WINDWARD TERRAIN OF COLORADO AND NORTHERN NEW MEXICO.
AGAIN...THERE WILL BE A CHANCE FOR ACCUMULATING SNOW TO SPREAD
EASTWARD OUT INTO THE RELATIVELY LOWER ELEVATIONS OF THE
CENTRAL/SOUTHERN HIGH PLAINS WHILE ADDITIONAL HEIGHT FALLS
PROGRESS EASTWARD SATURDAY INTO SUNDAY.

SOME OF THE GREATEST UNCERTAINTY IN THE FORECAST IS WITH HOW MUCH
SNOW CAN ACCUMULATE OVER THE LOWER ELEVATIONS...WHERE SUBTLE
SPREAD IN MODEL MASS FIELDS ARE LEADING TO CRITICAL DIFFERENCES IN
THE THERMAL PROFILES.  IN GENERAL...THE GFS/NAM HAVE BEEN COLDER
AND MORE AGGRESSIVE WITH ACCUMULATIONS THAN THE RELATIVELY WARMER
ECMWF.  THE LATEST DAY 1 WPC SNOWFALL PROBABILITIES EXTEND A
SLIGHT RISK (AT LEAST 10% PROBABILITY) OF SNOWFALL EXCEEDING 4
INCHES INTO WESTERN NEBRASKA...AND THE DAY 3 WPC PROBABILITIES ARE
HIGHLIGHTING A SLIGHT RISK OF SNOWFALL EXCEEDING 4 INCHES
EXTENDING FROM EASTERN COLORADO INTO CENTRAL NEBRASKA.


THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


GERHARDT

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