Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 210756
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
355 AM EDT THU SEP 21 2017

VALID 12Z THU SEP 21 2017 - 12Z SUN SEP 24 2017


DAYS 1-3...

NORTHERN ROCKIES

THE HIGHLY AMPLIFIED UPPER LEVEL PATTERN WILL CONTINUE TO CLOSE
OUT THE WEEK AND GOING INTO THE WEEKEND WITH AN ANOMALOUS UPPER
LEVEL TROUGH BECOMING RE-ESTABLISHED OVER THE WESTERN THIRD OF THE
CONTINENTAL U.S., WITH A POTENT SHORTWAVE DROPPING SOUTHWARD FROM
THE PACIFIC NORTHWEST COAST SERVING TO AMPLIFY THE TROUGH.  MODELS
ARE INDICATING 500MB HEIGHT ANOMALIES DROPPING TO 1-2 STANDARD
DEVIATIONS BELOW NORMAL ACROSS THE NORTHERN ROCKIES AS A CLOSED
CENTER DEVELOPS OVER IDAHO, WITH ANOMALOUSLY COLD THERMAL PROFILES
FOR LATE SEPTEMBER.  FAVORABLE UPPER LEVEL JET DYNAMICS ALONG WITH
700-850MB FRONTOGENESIS ARE EXPECTED TO CREATE A FAVORABLE
ENVIRONMENT FOR MODERATE TO HEAVY SNOW ACCUMULATIONS ACROSS MUCH
OF THE NORTHERN ROCKIES, AND SOME LIGHTER AMOUNTS FOR THE HIGHER
RANGES OF CENTRAL NEVADA AND EXTENDING AS FAR WEST AS THE SIERRA.


THE SURFACE LOW THAT WILL ACCOMPANY THE SHORTWAVE IMPULSE IS
EXPECTED TO TRACK ACROSS CENTRAL UTAH TO SOUTHERN WYOMING, WITH
MUCH LOWER FREEZING LEVELS OVER THE NORTHWEST WYOMING, WESTERN
MONTANA, AND CENTRAL IDAHO RANGES DURING THIS FORECAST PERIOD.
THE HEAVIEST SNOW IS EXPECTED FOR THE WIND RIVER AND ABSAROKA
MOUNTAINS, WHERE THE GREATEST PROBABILITIES OF AT LEAST A FOOT OF
SNOW EXIST.  NORTHEASTERLY FLOW NORTH OF THE FRONTAL BOUNDARY WILL
FAVOR THE NORTHERN AND EASTERN SLOPES.  SOME LIGHT SNOW IS
POSSIBLE FOR THE HIGHEST ELEVATIONS OF THE UINTAS AND THE COLORADO
ROCKIES, MAINLY ABOVE 10000 FEET.  THE SNOW IS EXPECTED TO TAPER
OFF DURING THE DAY 3 PERIOD ON SATURDAY WITH SURFACE HIGH PRESSURE
BUILDING IN WITH DRY AIR ADVECTION.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT
NATIONWIDE.

HAMRICK

$$





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