Quantitative Precipitation Forecast
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000
FOUS11 KWBC 092104
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 PM EST MON JAN 09 2017

VALID 00Z TUE JAN 10 2017 - 00Z FRI JAN 13 2017

...WESTERN U.S....

DEEP ANOMALOUS PACIFIC MOISTURE SPREADING ACROSS THE WESTERN U.S.
WILL PERSIST OVER THE NEXT FEW DAYS TO FUEL EXTREMELY HEAVY
PRECIPITATION AND VERY HEAVY MOUNTAIN SNOWS...WITH SEVERAL
ADDITIONAL FEET POSSIBLE FROM PORTIONS OF THE SIERRA TO PARTS OF
THE CENTRAL ROCKIES.

THE PATTERN STARTS OFF WITH RELATIVE FLAT ZONAL FLOW OVER THE PAC
AND A DOUBLE BARREL LOW JUST OFFSHORE OF THE NW. OVER THE FIRST 24
HRS... THE CLOSED LOW JUST OFFSHORE OF WA/OR WILL PARTIALLY FILL
AND SHEAR-OUT DOWNSTREAM... WHILE A VERY POTENT SHORT WAVE OVER
THE EAST CENTRAL PAC APPROACHES NRN CA/SRN OR. STEADY WRLY TO
WSRLY FLOW WILL INCREASE ESPECIALLY BY THE END OF THE PERIOD... AS
A SLUG OF 3 TO 4 TIMES ABOVE AVG 850-700MB MOISTURE FLUX SURGES
TOWARD CA AND THE WEST COAST. THE HEAVIEST SNOWFALL WILL OCCUR
FROM OR CASCADES/NRN CA MTNS AND SIERRA TO THE TETONS/NRN WASATCH
AND CO ROCKIES.

THEN TUES EVE TO WED EVE... THE EXPLOSIVE SHORT WAVE WILL PLOW
INTO NRN CA AND SHEAR DOWNSTREAM INTO THE INTER-MOUNTAIN WEST.
THIS IMPRESSIVE SLUG OF MOISTURE TRANSPORT WILL SPREAD DOWNSTREAM
AND ONCE AGAIN THE CORRIDOR FROM NRN CA MTNS/SIERRA TO THE
TETONS/NRN WASATCH AND CO ROCKIES ALONG WITH THE SAWTOOTH OF ID
WILL LIKELY SEE THE HEAVIEST SNOWFALL ACCUMULATIONS.

FINALLY THROUGH THURS... THE SECOND CLOSED LOW OFFSHORE OF THE PAC
NW WILL DIG SOUTH AND EAST TOWARD CENTRAL CA AND BRING THE LAST
HURRAH TO THIS ANOMALOUS MOISTURE EVENT. IN FACT... MOISTURE
TRANSPORT WILL BE ONLY SLIGHTLY ELEVATED... AS HEAVY SNOW WILL
OCCUR FROM THE SIERRA INTO CENTRAL/SRN WASATCH AND CO ROCKIES.


...UPPER MS VALLEY/GREAT LAKES/NORTHEAST...

A MULTI WINTER WEATHER THREAT WILL OCCUR OVER THE NEXT THREE DAYS
WITH HEAVIEST ACTIVITY OCCURRING MON EVENING TO TUES EVENING. PAC
UPPER DYNAMICS PROGRESSING THROUGH THE INTER-MOUNTAIN WEST TODAY
WILL EJECT INTO THE CENTRAL PLAINS TUES MORNING TO INDUCE A
SURFACE LOW OVER THE MID MS VALLEY. THIS SURFACE LOW WILL
INTENSIFY WHILE LIFTING UP TOWARD THE UP OF MI AS THE 500MB SHORT
WAVE TROUGH TAKES A NEG TILT. THIS SYSTEM WILL ALSO PARTIALLY
PHASE WITH A RE-ENFORCING SHOT OF ARCTIC AIR... SO THE WEST TO
EAST PLUME OF OVERRUNNING PRECIP FROM WI TO THE ERN LAKES SHOULD
EVENTUALLY GIVE WAY TO A DEVELOPING DEFORMATION ZONE/COMMA HEAD
OVER WI INTO THE UP OF MI. THE HEAVIEST SNOWFALL APPEARS LIKELY
ACROSS NERN WI AND NRN LOWER MI WITH PERHAPS SOME LIGHT ICING ON
THE SRN EDGE OF THE PRECIP SHIELD BEFORE WARM ADVECTION OVERTAKES
THE RETREATING COLD AIR MASS.

AS THIS AREA OF CYCLOGENESIS DEPARTS THE UPPER GREAT LAKES... THE
MAJORITY OF WED WILL MAINLY BE QUIET. HOWEVER TOWARD WED
AFTN/EVENING THROUGH THURS EVENING... THE SAME SETUP OF PAC UPPER
DYNAMICS ARRIVING FROM UPSTREAM WILL TEAM WITH ANOTHER SURGE OF
ARCTIC AIR TO PRODUCE A STREAK OF SNOW AND ICE. A SURFACE WAVE
DEVELOPING OVER MO WILL SHIFT OFF TO THE NORTH AND EAST TOWARD
LAKE ONTARIO AND ALLOW THE A COLD DENSE AIR MASS TO SLICE SOUTH
AND EAST. THE HEAVY SNOWFALL AXIS WILL OCCUR FROM WI INTO MI AND
ICING WILL POTENTIALLY OCCUR FROM ERN IA/NERN MO AND NRN IL INTO
LOWER MI.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

MUSHER

$$





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