Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 222038
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
337 PM EST SAT NOV 22 2014

VALID 00Z SUN NOV 23 2014 - 00Z WED NOV 26 2014


...PACIFIC NORTHWEST/GREAT BASIN/NORTHERN AND CENTRAL ROCKIES...

THE PERSISTENT AND POWERFUL 300 MB JET IS FCST TO EXTEND ACROSS
OR/NV/SOUTHERN UT WITH DIVERGENCE MAXIMA IN THE LEFT EXIT REGION
OF THE JET ACROSS THE RANGES FROM THE WA CASCADES TO ID/WASATCH OF
UT AND RANGES OF WESTERN CO.  ASCENT IS AIDED WITH FRONTAL
CONVERGENCE IN CO TONIGHT...SO HIGHER PROBABILITIES ARE SHOWN
THERE AS THE FRONTAL SNOW IS FOLLOWED BY FAVORABLE UPSLOPE
CONDITIONS.
THE WA CASCADES HAVE HIGH PROBABILITIES AS EVENING UPSLOPE FLOW
GETS AUGMENTED BY STRONG 700 MB CONVERGENCE ON THE NOSE OF A 700
MB JET COMING ONSHORE SUN MORNING AND CROSSING THE CASCADES
SHORTLY THEREAFTER. A RESPITE DEVELOPS NEAR 00Z MON AS A BUILDING
UPSTREAM 700 MB RIDGE STARTS INDUCING DRYING AND SINKING MOTION.

ENHANCED 700 MB CONVERGENCE OCCURS ON DAY 2 IN THE TETONS OF WY TO
THE RANGES OF WESTERN CO WITH
THE CORRESPONDINGLY ENHANCED OROGRAPHIC ASCENT PROVIDING THE
MAJORITY OF SNOWFALL FOR THE WINDWARD SLOPES OF THE MOUNTAINS.  IN
WA/ID...THE APPROACHING 300 MB JET MAX CONTAINS UPPER DIVERGENCE
MAX TO AID IN PRODUCING ASCENT THROUGH MONDAY.

ON DAY 3 THE 300 MB JET SHIFTS FURTHER INLAND WITH ASCENT
CONTINUING AS THE NOSE OF THE 700 MB JET NEAR 60-65 KT CROSSES WA
AND NORTHERN ID.   THE MODELS FCST A SURGE OF HEAVY PRECIPITATION
WITH WARM/MOIST ADVECTION PERSISTING ALONG WITH HIGH LAYER RH OF
90-99 PERCENT.  THE PRIMARY UNCERTAINTY IS CLIMBING SNOW
ELEVATIONS AS WARM ADVECTION CONTINUES...SO SNOW MAY CHANGE TO
RAIN IN MOST OF THE WA CASCADES. THE 700 MB WAR/MOISTURE ADVECTION
AND AREAS OF CONVERGENCE MOVE DOWNSTREAM ACROSS THE RANGES OF
WESTERN AND CENTRAL MT INTO WESTERN WY...CONTINUING THE THREAT OF
MODERATE TO HEAVY SNOWS.
THE DETERMINISTIC AND PROBABILISTIC TOTALS WERE GIVEN MORE WEIGHT
FROM THE 09Z SREF MEAN ALONG WITH THE 12Z NAM AND 00-12Z ECMWF.


...UPPER GREAT LAKES...

THERE REMAINS POTENTIAL FOR HEAVY SNOW FOR PARTS OF WISCONSIN AND
THE UPPER PENINSULA OF MICHIGAN MONDAY INTO MONDAY NIGHT.  THE
MODELS/ENSEMBLE MEANS CONTINUE WITH A WIDE SPREAD IN BOTH THE
STORM TRACK AND RATE OF CYCLONE INTENSIFICATION.. THE 12Z GFS
REACHES RECORD INTENSITY WITH THE SURFACE LOW PRESSURE AS IT
REACHES THE UP OF MI MONDAY MORNING...SIGNIFICANTLY DEEPER THAN
OTHER LOWS.  THUS LESS WEIGHTING WAS GIVEN TO THE GFS/GFS PARALLEL
SOLUTIONS.
THE 00Z ECMWF STARTED WITH A LOW TRACK FURTHER EAST...WITH THE 12Z
ECMWF THROWING IN A TREND TOWARDS FASTER MOTION AS WELL...MEANING
LESS PRECIP WOULD WRAP AROUND THE LOW LEVEL CYCLONE WEST INTO WI.
THE 12Z NAM HAD A SLOWER FORWARD MOTION ALLOWING MORE PRECIP IN
THE COLD SECTOR AND GREATER SNOW POTENTIAL.

INITIAL TEMPERATURES START AS TOO WARM FOR SNOW IN WI.  AS THE
CYCLONE DEEPENS AND PASSES BY...RAPID LOW LEVEL COLD ADVECTION
LEADS TO A CHANGE OVER FROM RAIN TO SNOW STARTING IN NORTHEAST MN
THEN CROSSING THE UP OF MI AND WI.  THE COMBINED UNCERTAINTIES
LEAVE PROBABILITIES AS HIGHER IN FAVORED LK ENHANCED AREAS
DOWNSTREAM OF LK SUPERIOR IN THE UP OF MI AND LOW TO MODERATE
ELSEWHERE IN SURROUNDING AREAS.   CYCLONE`S CIRCULATION TO HELP
GENERATE SNOWFALL PRODUCTION.  E CASE...THE PRECISE LOCATION OF
THE RAIN/SNOW LINE WILL LIKELY WAVER THE NEXT COUPLE DAYS...AS
WELL AS THE CYCLONE`S EXACT PATH AND DEPTH...ALL WHICH WILL
INFLUENCE THE LIKELIHOOD AND AMOUNT OF SNOW.  FOR THIS PARTICULAR
FORECAST PACKAGE...THE ABOVE SOLUTIONS WERE USED THE CREATE THE
DETERMINISTIC SNOW AMOUNTS.

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

PETERSEN




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