Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 021945
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
344 PM EDT SAT MAY 02 2015

VALID 00Z SUN MAY 03 2015 - 00Z WED MAY 06 2015

...SNOW...

...CO ROCKIES - CONDITIONS WILL SUPPORT WIDESPREAD DIURNALLY
DRIVEN SHOWER ACTIVITY SUNDAY AND MONDAY AFTERNOON/EVENING...BUT
ABOVE NORMAL TEMPERATURES ACROSS THE REGION SHOULD KEEP  SNOW
ACCUMULATIONS CONFINED TO THE HIGHEST PEAKS OF THE COLORADO
ROCKIES.  TEMPERATURES FALL AS THE UPPER LOW EJECTS ACROSS THE
FOUR CORNERS INTO CO..WITH SNOW ACCUMULATIONS MORE LIKELY AT
HIGHER ELEVATIONS ABOVE 10K FT. THE PRIMARY THREAT FOR SIGNIFICANT
ACCUMULATIONS APPEARS TO BE IN THE SAN JUAN MNTNS OF SOUTHWEST CO
INTO THE RANGES OF CENTRAL CO.

LOW ACCUMULATIONS IN THE GFS/ECMWF/12Z NAM/12Z UKMET RESULTED IN
SLIGHT RISK AREAS OF AT LEAST 4 INCHES OF SNOW DURING THE DAY 2
AND 3 FORECAST PERIODS.  THERE WAS BETTER THAN AVERAGE AGREEMENT
IN THE TIMING OF THE MID-UPPER LEVEL TROUGH.

...PACIFIC NORTHWEST...
HEIGHT FALLS AND TEMPERATURE DECLINES OCCUR AS THE BROAD 700-500
MB CIRCULATION APPROACHES BRITISH COLUMBIA.  SOUTH OF THE
CIRCULATION...BANDS OF 700 MB CONVERGENCE/300 MB CONVERGENCE
DEVELOP WITH SHOWERS EXPECTED IN THE OLYMPICS AND CASCADES OF WA.
GFS FCST SOUNDINGS SHOW LAYERS OF DESCENDING MOTION WITH UPSLOPE
CONDITIONS NEEDED TO AID ASCENT.  THE FLOW GRADUALLY WEAKENS WITH
TIME AS THE MID LEVEL CIRCULATION APPROACHES. LOW ACCUMULATIONS IN
THE GFS/ECMWF/09Z SREF MEAN/12Z NAM RESULTED IN SLIGHT RISK AREAS
OF AT LEAST 4 INCHES OF SNOW DURING THE DAY 2 AND 3 FORECAST
PERIODS.

...ICE...

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

PETERSEN



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