Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 260815
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
314 AM EST THU FEB 26 2015

VALID 12Z THU FEB 26 2015 - 12Z SUN MAR 01 2015


...GREAT BASIN/CENTRAL TO SOUTHERN ROCKIES/CA/OR...

AN EXTENDED PERIOD OF HEAVY SNOW IS POSSIBLE FOR THE RANGES OF
SOUTHERN UT/NORTHERN AZ/SOUTHERN CO/NORTHERN NM.

THE MAIN THREAT ON THURS WILL BE IN THE FRONT RANGE AND FOOTHILLS
OF SOUTHERN CO AND NM...AS UPPER DIVERGENCE/LOWER CONVERGENCE
MAXIMA PERSISTS ESPECIALLY IN THE SANGRE DE CRISTO RANGE. LOW
LEVEL FRONTOGENESIS AIDS UPSLOPE FLOW IN PRODUCING SNOW.  THE
SYSTEM PRODUCED SEVERAL INCHES OF SNOW UPSTREAM IN CO WED AND
SHOULD DO SO AGAIN IN NM THU.  LIGHT SNOWS SPREAD OUT ON THE
PLAINS OF THE TX PANHANDLE AS THE UPPER DIVERGENCE MAXIMA TRACKS
EAST FROM NM.

THEN ON FRI ... UPPER HEIGHT FALLS AND A POWERFUL DIGGING UPPER
JET WILL RESULT IN THE UPPER FLOW BACKING AND UPPER JET
INTENSIFYING WITH A 300 MB JET CROSSING CA THROUGH SOUTHERN NV
INTO NORTHERN AZ AND NM.  FAVORABLE SOUTHWESTERLY UPPER DIFLUENT
FLOW IN THE LEFT EXIT REGION OF THE UPPER JET LEADS TO COUPLED
UPPER DIVERGENCE/LOWER CONVERGENCE MAXIMA ACROSS SOUTHERN UT AND
CO.

850-700 MB WARM/MOISTURE ADVECTION ON THE PLAINS OF THE TX
PANHANDLE LEADS TO ANOTHER ROUND OF LIGHT SNOW...EXTENDING EAST
INTO NORTHERN CENTRAL TX AND ACROSS THE RED ROVER INTO OK AS THE
WARM/MOISTURE ADVECTION SPREADS NORTHEAST WITH TIME AS THE UPPER
JET DRIFTS NORTH ACROSS THE REGION WITH EMBEDDED UPPER DIVERGENCE
MAXIMA.

ON SAT THE UPPER JET PERSISTS OVER THE FOUR CORNERS...ALLOWING
UPPER DIVERGENCE TO PERSIST OVER MUCH OF SOUTHERN CO AND NM.  THE
AREA MOST LIKELY TO SEE VERY HEAVY SNOWFALL WILL BE IN SWRN CO
ACROSS THE SAN JUANS.  MID LEVEL FRONTOGENESIS COMBINES WITH
PERSISTENT MOIST FLOW TO PRODUCE MODERATE TO LOCALLY HEAVY SNOW
FURTHER NORTH IN THE RANGES OF CO.

PERSISTENT SNOW SHOWERS ARE EXPECTED THU AND FRI OVER THE OR
CASCADES AS THE UPPER TROUGH CROSSES THE REGION...ALLOWING FALLING
SNOW ELEVATIONS AND FOR THE COLUMN TO MOISTEN.  STEEPENING LAPSE
RATES OF 7-8 DEG C/KM ALLOW SNOW SHOWERS TO PERSIST AS THE AREA
GETS INTO THE COLD SECTOR.

MANUAL PROGS GAVE MORE WEIGHTING TO THE 12-00Z ECMWF /00Z GFS AND
21Z SREF MEAN QPF/TEMPERATURE PROFILES FOR SNOW AMOUNTS AND
PROBABILITIES.

...DAY 3 IN THE CENTRAL PLAINS TO MID MS VALLEY...

THE MODELS INDICATE RETURN LOW LEVEL SOUTH TO SOUTHWEST FLOW TO
ADVECT MOISTURE NORTH FROM THE SOUTHERN TO CENTRAL PLAINS
NORTHEAST TO THE MID MS VALLEY...WITH PRECIPITABLE WATER VALUES AS
HIGH AS HALF AN INCH BY SAT NIGHT.
THE MODELS SHOW UPPER DIVERGENCE MAXIMA DEVELOPING WITHIN A
MODESTLY COUPLED UPPER JET REGION CROSSING FROM THE CENTRAL PLAINS
NORTHEAST TO THE MID MS VALLEY.
LOW LEVEL CONVERGENCE DEVELOPS UNDERNEATH THE UPPER DIVERGENCE
MAXIMA...RESULTING IN PRECIP BREAKING OUT ACROSS THE REGION...WITH
SNOW WHERE TEMPS REMAIN BELOW FREEZING.
THE PRECIP TYPE TRANSITION ZONE LOOKS TO MOVES OUT OF TX ACROSS
EASTERN OK/SOUTHEASTERN KS AND SOUTHERN MO...WHERE WARMING ALOFT
CHANGES SNOW TO SLEET AND FREEZING DRIZZLE OR LIGHT FREEZING RAIN.

MANUAL PROGS GAVE MORE WEIGHTING TO THE 12-00Z ECMWF /00Z GFS AND
21Z SREF MEAN QPF/TEMPERATURE PROFILES FOR SNOW AMOUNTS AND
PROBABILITIES.

THE PROBABILITY OF 0.25 INCHES OR GREATER ICING IS LESS THAN 10
PERCENT.

PETERSEN

$$





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