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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0701Z Apr 30, 2018)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
301 AM EDT MON APR 30 2018

VALID 12Z MON APR 30 2018 - 12Z THU MAY 3 2018

WITH THE DEPARTURE OF THE HIGHER ELEVATION SNOW ACROSS THE
NORTHEAST U.S. EARLY MONDAY, WINTER WEATHER WILL BE RELEGATED TO
THE INTERMOUNTAIN WEST AND THE ROCKY MOUNTAINS FOR THE BEGINNING
TO MIDDLE OF THE WEEK WITH A LARGE SCALE MID-UPPER LEVEL TROUGH
BECOMING FIRMLY ESTABLISHED OVER THE REGION.

THE FIRST FEATURE OF INTEREST WILL BE AN INVERTED SURFACE TROUGH
AND ACCOMPANYING 700MB LOW DEVELOPING OVER NORTHERN UTAH AND INTO
WYOMING BY THE BEGINNING OF THE DAY 1 PERIOD MONDAY MORNING, AND
THE LAST FEW RUNS OF THE GFS HAVE INDICATED THE GREATEST
REFLECTION OF THIS FEATURE.  THE COMBINATION OF STRONG 700MB
FRONTOGENETICAL FORCING, LEFT EXIT JET DYNAMICS, AND BOUNDARY
LAYER UPSLOPE FLOW IS EXPECTED TO RESULT IN SIGNIFICANT LATE
SEASON SNOW FROM THE NORTHERN WASATCH AND UINTA MOUNTAINS OF UTAH,
AND PARTICULARLY THE ABSAROKA, WIND RIVER, AND BIG HORN MOUNTAINS
OF WYOMING.  THE POTENTIAL EXISTS FOR ACCUMULATIONS IN EXCESS OF
12 INCHES ABOVE 8000 FEET, AND SOME ENSEMBLE MEMBERS ARE
INDICATING THIS SCENARIO.  THE THERMAL PROFILE IS BASED ON A BLEND
OF THE 00Z GFS/NAM AND 12Z ECMWF WITH LOCAL ADJUSTMENTS FOR
TERRAIN.

THE SECOND FEATURE WILL BE A CLOSED LOW THAT IS FORECAST TO
DEVELOP AT THE BASE OF THE TROUGH OVER THE SOUTHWEST US.  THE
SHORTWAVE PERTURBATION SHOULD TRACK ROUGHLY PARALLEL TO THE WEST
COAST THROUGH TUESDAY MORNING BEFORE EVOLVING INTO A CLOSED
MID-UPPER LEVEL LOW OVER SOUTHERN NEVADA BY TUESDAY NIGHT. 
ENHANCED UPPER LEVEL DIVERGENCE AND BOUNDARY LAYER CONVERGENCE IN
THE VICINITY OF THE LOW-MID LEVEL FRONT IS EXPECTED TO DEVELOP AS
IT CROSSES THE SIERRA NEVADA MOUNTAINS TUESDAY, AND SHOULD
CONTINUE DOWNSTREAM IN TANDEM WITH THE FRONT ACROSS NEVADA AND
THEN THE WASATCH MOUNTAINS.  BOTH THE GFS AND ECMWF SHOW 300 MB
DIVERGENCE DEVELOPING IN NORTHERN COLORADO WEDNESDAY AFTERNOON
OWING TO LEFT EXIT JET DYNAMICS, AND THIS WOULD SUPPORT INCREASING
COVERAGE OF SNOW SHOWERS.  THE QPF AND THERMAL PROFILES WERE BASED
ON A BLEND OF THE 00Z GFS/NAM AND 12Z ECMWF/EC MEAN.

D. HAMRICK