Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 222110
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
410 PM EST WED FEB 22 2017

VALID 00Z THU FEB 23 2017 - 00Z SUN FEB 26 2017

...NORTHERN AND CENTRAL ROCKIES TO THE UPPER MIDWEST...

HEAVY SNOWS ARE EXPECTED ACROSS PORTIONS OF THE ROCKIES FROM
SOUTHWESTERN MT TO UT AND NORTHERN CO AND THEN ALONG A NARROW AXIS
EXTENDING EAST ACROSS SOUTHERN SD AND NORTHERN NEB AND
NORTHEASTWARD ACROSS THE MID MO AND UPPER MS VALLEYS INTO THE
UPPER GREAT LAKES REGION.

A WELL-DEFINED SHORTWAVE MOVING THROUGH THE BASE OF A BROAD UPPER
TROUGH IS EXPECTED TO MOVE ACROSS THE GREAT BASIN INTO THE CENTRAL
ROCKIES LATE WED INTO THU MORNING.  INCREASING EASTERLY FLOW IN
CONCERT WITH LOW TO MID LEVEL FRONTOGENESIS AND FAVORABLE FORCING
ALOFT IS EXPECTED TO SUPPORT HEAVY SNOWS ALONG THE CENTRAL AND
EASTERN WY RANGES...EXTENDING EAST INTO WESTERN NEB AND SOUTHERN
SD...WITH ACCUMULATIONS OF A FOOT OR MORE POSSIBLE BY THU EVENING.

LATE THU...GUIDANCE SHOWS THE SHORTWAVE ASSUMING A NEGATIVE TILT
AS IT MOVES FROM THE CENTRAL ROCKIES INTO THE HIGH PLAINS WITH A
STRONG SURFACE LOW MOVING OUT ACROSS KS.  AS A MID-UPPER LEVEL
CENTER CLOSES OFF OVER THE CENTRAL PLAINS THE LOW IS EXPECTED TO
TURN TO THE NORTHEAST...TRACKING ACROSS THE MID MO VALLEY THU
NIGHT.  STRONG LOW LEVEL WARM ADVECTION AND FAVORABLE UPPER JET
DYNAMICS IS EXPECTED TO SUPPORT A BAND OF MODERATE TO HEAVY SNOWS
DEVELOPING AHEAD OF THE LOW...LIFTING NORTHEAST FROM THE MID MS
VALLEY INTO THE UPPER GREAT LAKES THU NIGHT-FRI MORNING.
MEANWHILE...HEAVY SNOWS ARE EXPECTED TO DEVELOP ON THE NORTHWEST
SIDE OF THE SURFACE LOW...WITH LOW TO MID LEVEL FRONTOGENESIS
SUPPORTING BANDED HEAVY SNOW FROM SOUTHEASTERN SD AND EASTERN NEB
INTO NORTHERN IA...SOUTHERN MN AND CENTRAL WI.  FOR THE 24-HR
PERIOD ENDING FRI EVENING...WPC PROBABILISTIC GUIDANCE SHOWS AT
LEAST A SLIGHT RISK FOR ACCUMULATIONS OF A FOOT OR MORE.

THE LOW IS EXPECTED TO QUICKLY LIFT TO THE NORTH ACROSS THE GREAT
LAKES...WITH THE HEAVY SNOW THREAT QUICKLY DIMINISHING AS THE LOW
TRACKS INTO SOUTHERN ONTARIO SAT MORNING.

WITH THE MODELS IN FAIRLY GOOD AGREEMENT...THE WPC FORECAST
FOLLOWED A BLEND OF THE NAM...GFS AND THE ECMWF THROUGH THU
EVENING.  BEYOND DAY 1 HOWEVER...THE MODELS BEGIN TO DIVERGE WITH
THE NAM...THE SREF AND A FEW OF THE HI-RES MEMBERS...SLOWER AND
MORE AMPLIFIED WITH THE LOW THAN THE GFS AND ECMWF.  THE WPC
FORECAST GAVE MORE WEIGHT TO RECENT RUNS OF THE GFS AND THE
ECMWF...KEEPING HEAVIER AMOUNTS FURTHER TO THE SOUTH ACROSS THE
PLAINS AND UPPER MIDWEST.  ALTHOUGH THE GFS AND ECMWF HAVE BEEN
FAIRLY CONSISTENT OVER THEIR PAST FEW RUNS...THEY HAVE SHOWN A
SLIGHT SHIFT TO THE SOUTH...WHICH IS REFLECTED IN THE WPC FORECAST
AS WELL.  IN ADDITION TO FORECAST SPREAD...FORECAST CONFIDENCE IS
LIMITED BY WHAT SOME OF THE GUIDANCE SHOWS TO BE A PRONOUNCED DRY
SLOT BEHIND THE INITIAL SHOT OF WARM ADVECTION
PRECIPITATION...WHICH MAY IN TURN LIMIT ACCUMULATIONS ACROSS
PORTIONS OF THE UPPER MIDWEST.

THE PROBABILITY OF ICE ACCUMULATIONS GREATER THAN 0.25 IS LESS
THAN 10 PERCENT DAYS 1-3.

PEREIRA

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