Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 180807
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
407 AM EDT SAT APR 18 2015

VALID 12Z SAT APR 18 2015 - 12Z TUE APR 21 2015

...CENTRAL ROCKIES...

THE SNOW THREAT ASSOCIATED WITH A SLOW MOVING UPPER LOW AND LOW
LEVEL UPSLOPE FLOW AND UPPER DIVERGENCE MAXIMA IS EXPECTED TO
CONTINUE FOR ANOTHER DAY ACROSS PORTIONS OF THE MOUNTAINS OF
NORTHERN CO TO SOUTHEAST WY. SEVERAL MORE INCHES ARE POSSIBLE
BEFORE THE EVENT ENDS. BY EARLY SUN EXPECT THE HEAVY SNOW THREAT
TO WANE AS THE UPPER LOW WEAKENS AND EJECTS OUT ACROSS THE CENTRAL
PLAINS. A 700 MB WAVE TRAVERSES WY FROM NORTHWEST TO SOUTH CENTRAL
WY/ADJACENT CO WITH CONFLUENT FLOW RESULTING IN WEAK 700 MB
VERTICAL VELOCITY MAXIMA AND A FEW ADDITIONAL INCHES OF SNOW
EXPECTED.
MANUAL PROGS USED THE 12-00Z ECMWF AND 00Z GFS/21Z SREF MEAN QPF
AND TEMPERATURE PROFILES FOR THE SNOW FORECAST AND PROBABILITIES.


...NORTHERN MN AND NORTHERN WI...

PRECIPITATION WILL SPREAD ACROSS THE AREA AS A MID-UPPER LEVEL
TROUGH DRIFTS EAST ACROSS THE REGION.  RAIN CHANGING TO SNOW IS
EXPECTED SUN NIGHT-MON...AS THE NORTHERN STREAM TROUGH
AMPLIFIES...WITH POST FRONTAL COLD ADVECTION LOWERING
TEMPERATURES.  BANDS OF ENHANCED MOISTURE AND LOW LEVEL
CONVERGENCE ROTATE THROUGH THE BASE OF THE TROUGH...RESULTING IN
SNOW SHOWERS IN THE REGION.
THE WEAK ASCENT AND SHOWERY NATURE OF THE PRECIP SUGGEST LITTLE
CHANCE OF A HEAVY SNOW EVENT.  PERSISTENT SHOWERS IN FAVORABLE
DEFORMATION BANDS SHOULD RESULT IN ACCUMULATING SNOWS ACROSS
PORTIONS OF NORTHERN MN AND NORTHERN WI LATE SUN INTO MON.
THE MODELS DIFFER ON THE TIMING OF THE DEEP LAYER TROUGH AND QPF
WITHIN THE AREA COLD ENOUGH FOR SNOW.  MORE WEIGHTING WAS GIVEN TO
THE 12-00Z ECMWF AND GFS SOLUTIONS THAN OTHER FORECASTS.

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

PETERSEN


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