Quantitative Precipitation Forecast
Issued by NWS

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885 FOUS11 KWBC 230737 QPFHSD PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 337 AM EDT SAT SEP 23 2017 VALID 12Z SAT SEP 23 2017 - 12Z TUE SEP 26 2017 DAYS 1-3... ...GREAT BASIN AND CENTRAL TO NORTHERN ROCKIES... A SLOW MOVING LOW LEVEL FRONTAL BNDRY COMBINES WITH AN UPPER TROUGH TO PRODUCE AREAS OF SNOW IN HIGHER ELEVATIONS ACROSS UT/WY/NORTHERN CO OVER THE NEXT FEW DAYS. THE THREAT WANES ONCE THE UPPER TROUGH WEAKENS AND MOVES NORTHEAST EARLY NEXT WEEK. THE INITIAL CIRCULATION DRIFTS NORTHEAST FROM UT INTO WY ON DAY 1. 700 MB CONVERGENCE NEAR THE LOW PRODUCES ASCENT...AIDED IN THE RANGES OF WESTERN WY LIKE THE WIND ROVER WHERE MOIST EASTERLY FLOW TURNS UPSLOPE SAT NIGHT-SUN MORNING. ON DAY 1 SNOW FALL AMOUNTS TIED MORE CLOSELY TO THE CANADIAN REGIONAL GEM AND THE MEAN OF THE HIGH RESOLUTION WINDOW FORECASTS. ON DAY 2...THE INITIAL CIRCULATION IS FORECAST TO DRIFT NORTHEAST FROM THE UT UINTA MOUNTAINS ACROSS WY AND GRADUALLY WEAKEN. PERSISTING 700 MB CONVERGENCE LEADS TO CONTINUING SNOW IN THE UT UINTAS/SOUTHWEST WY THAT SPREAD ACROSS THE BIGHORNS AND MEDICINE BOW/LARAMIE MNTS. THE MODELS SPLIT ON MONDAY/TUE THE PHASING OF THE UPPER TROUGH ONCE THE INITIAL LEAD WAVE EXITS THROUGH THE NORTHERN PLAINS. THE 00Z NAM DEVELOPS AN ANOMALOUS 700 MB CIRCULATION IN CO...LEADING TO HEAVIER SNOW TOTALS THAN THE OTHER MODELS IN THE CO RANGES. LESS WEIGHTING WAS GIVEN TO THE NAM UNTIL OTHER MODELS JOIN ITS SOLUTION. THE ECMWF/GFS FORECASTS HAVE RELATIVELY LIGHT AMOUNTS GIVEN WEAK LOW LEVEL WINDS AND RESULTANT MODEST CONVERGENCE SIGNALS. THE MAJORITY CLUSTER OF SOLUTIONS WAS PREFERRED AND GIVEN THE MOST WEIGHTING. THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. PETERSEN $$

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