Quantitative Precipitation Forecast
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FOUS11 KWBC 262126
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
426 PM EST SAT NOV 26 2016

VALID 00Z SUN NOV 27 2016 - 00Z WED NOV 30 2016

DAY 1 TO 3...

...WESTERN U.S...

ON DAY ONE...THE UPPER TROUGH STREAMS ONSHORE INTO INLAND INTO THE
NORTHERN ROCKIES AND GREAT BASIN. THE INITIAL UPPER JET CROSSES
FROM SOUTHERN CA AND NV EAST ACROSS SOUTHERN UT AND CO.  FAVORED
LEFT EXIT REGION DIVERGENCE MAXIMA PRODUCE PERIODS OF SNOW ACROSS
THE CA SIERRA AND THEN INTO THE HIGHER ELEVATIONS OF THE SOUTHERN
WASATCH AND SAN JUANS OF CO...WHERE LOCALLY HEAVY SNOW IS
EXPECTED. THE DEEP SOUTHWEST FLOW IS AUGMENTED BY FAVORABLE 7-8
DEG/KM LAPSE RATES IN ENHANCING RESPONSE TO THE LIFT IN WESTERN
CO. PRE-FRONTAL CONVERGENCE LEADS TO A PERIOD OF SNOW IN THE
RANGES OF WESTERN WY AND NORTHEAST UT.

ON DAY TWO...CONFLUENT FLOW OVER THE NORTHEAST PACIFIC PRODUCES
ANOTHER WELL DEFINED UPPER JET MAXIMA COMING ONSHORE INTO SOUTHERN
WA AND OR...WITH THE ECMWF PRODUCING A JET MAX OF 150-160 KT.
UPPER DIVERGENCE MAXIMA ASSOCIATED WITH THE JET CORE IS EXPECTED
TO COMBINE WITH UPSLOPE FLOW
AND FAVORABLE LAPSE RATES TO PRODUCE A PERIOD OF MODERATE TO HEAVY
SNOW ACROSS THE OR CASCADES AND SOUTHERN WA CASCADES.  THE JET
MOVES FURTHER INLAND TO BRING SNOW INTO THE BLUE MNTNS OF
NORTHEAST AND RANGES IN ADJACENT ID.

AS THE UPPER LEVEL RIDGE OVER THE EASTERN PACIFIC ARCS EAST...SNOW
COVERAGE MON NIGHT INTO TUE DECREASES OVER THE NORTHWEST.  DRIER
AIR MOVES INTO THE REGION DOWNSTREAM FROM THE UPPER RIDGE...SO THE
PRIMARY AREA OF CONCERN WILL BE IN UT AND WESTERN CO...WHERE
POCKETS OF MOISTURE AND LIFT EAST OF THE UPPER JET WILL CAUSES A
FEW AREAS OF LIGHT ACCUMULATING SNOW IN TERRAIN.  IN THE ABSENCE
OF AREAS OF PERSISTENT UPPER DIVERGENCE/LOWER CONVERGENCE
COUPLETS...IT WAS HARD TO IDENTIFY A HEAVY SNOW THREAT AREA TUE.

...NORTHERN PLAINS...

A SIGNIFICANT SNOWSTORM IS EXPECTED SUN AND MON ACROSS THE NRN
PLAINS/UPPER MIDWEST.
A SURFACE LOW DEVELOPS OVER CENTRAL NE AND DEEPENS AS IT DRIFTS
ACROSS ACROSS THE DAKOTAS. THE MOISTURE WRAPS AROUND THE AREA OF
LOW PRESSURE AND ONCE IT REACHES THE COLD SECTOR...A MID LEVEL
DEFORMATION AND FRONTOGENESIS ZONE WILL PRODUCE ASCENT WEST OF THE
CIRCULATION AND RESULT IN SNOW.  THE EXPECTED ZONE OF HEAVY
SNOWFALL APPEARS LIKELY FROM CENTRAL/ WESTERN ND AND SD STARTING
LATE SUN THROUGH MON.  THE CIRCULATION MOVES SLOWLY SO THE BANDS
MAY ROTATE FURTHER WEST INTO EASTERN MT AND WY...INCLUDING AS FAR
WEST AS THE BLACK HILLS AND BIGHORNS NEAR THE WY/MT BORDER.  THE
PRECIP TYPE TRANSITION ZONE IS ACROSS THE DAKOTAS SO THE
UNCERTAINTY OF QPF IS FURTHER COMPOUNDED BY THE UNCERTAINTY OF THE
DURATION OF SNOW IN THE CENTRAL DAKOTAS. THE GFS AND GEFS MEAN
MOVE THE LOW LEVEL CIRCULATION FURTHER NORTH THAN THE
ECMWF/UKMET/CANADIAN GLOBAL...WHICH IMPACTS THE QPF AMTS AND
PRECIP TYPE.  CONFIDENCE IS AVERAGE WITH A TYPICAL SPREAD IN
CYCLONE TRACK AND QPF AMOUNTS.

...MAINE...

A SHORT WAVE ROUNDING THE BASE OF AN UPPER TROUGH OVER THE NE WILL
INDUCE A SURFACE LOW IN THE OFFSHORE WATERS. THIS LOW WILL
INTENSIFY RAPIDLY WHILE LIFTING NORTHWARD AND THEN NORTHWEST OVER
TIME. ENOUGH ATLANTIC MOISTURE WILL FEED ALONG A RELATIVELY NARROW
AXIS OF THE INVERTED TROUGH THAT PERSISTS OVER MAINE TO PRODUCE
PRECIP...WITH SNOW IN NORTHERN MAINE AND RAIN NEAR THE COAST. WITH
THE STORM TRACK WELL AWAY...POTENTIAL FOR HEAVY SNOW HAS COME
DOWN. THE SNOW SHOULD DISSIPATING ON SUN AS THE STORM DEPARTS.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PETERSEN

$$





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