Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 210843
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
343 AM EST SUN JAN 21 2018

VALID 12Z SUN JAN 21 2018 - 12Z WED JAN 24 2018


...CENTRAL ROCKIES AND PLAINS THROUGH UPPER MS VALLEY INTO GREAT
LAKES/NORTHERN NEW ENGLAND...

A MULTI-DAY WINTER STORM WILL IMPACT A LARGE PORTION OF THE
COUNTRY TODAY THROUGH THE EARLY PART OF NEXT WEEK WITH HEAVY
SNOWFALL AND A POSSIBLE TRANSITION ZONE OF FREEZING RAIN/SLEET.

A PRONOUNCED SOUTHERN STREAM TROUGH IS LOCATED EARLY THIS MORNING
OVER THE FOUR CORNERS REGION. THIS INTENSE STORM SYSTEM WILL EJECT
AND DEEPEN OUT OVER THE PLAINS TODAY, WITH A LARGE CLOSED 500MB
LOW PROGRESSING FROM CO/NORTHERN NM INTO KS, WHILE A DEVELOPING
WAVE OF SURFACE LOW PRESSURE WILL FORM NEAR THE NWRN TX PANHANDLE
AND TRACK NORTHEASTWARD TOWARD NERN KS/NWRN MO. THIS SURFACE
LOW WILL GRADUALLY BEGIN THE PROCESS OF CYCLOGENESIS AND
CAPITALIZE ON INCREASING MOISTURE CONTENT FROM THE GULF OF MEXICO
FOR A FULL-FLEDGED WINTER CYCLONE TO DEVELOP. THE OVERNIGHT
GUIDANCE SHOWS VERY MINIMAL SPREAD WITH MASS FIELDS AND CONVERGING
MODEL SOLUTIONS PROVIDED CONFIDENCE ON CRITICAL THERMALS. IN FACT,
WPC WAS ABLE TO USE A MULTI-MODEL CONSENSUS FOR PTYPE. THE NWRN
SECTION OF THE STORM SYSTEM WILL LIKELY SEE A FLOURISHING
DEFORMATION ZONE AND COMMA HEAD OF INTENSE BANDING HEAVY SNOW FROM
NERN CO/NWRN KS AND SWRN NE THROUGH ALL OF CENTRAL NE INTO THE
NERN PORTION OF CORN-HUSKER STATE. MEANWHILE, A POTENTIALLY
PROMINENT TRANSITION ZONE OF SLEET/FREEZING RAIN APPEARS POSSIBLE
FROM NORTHERN IA AND SERN MN THROUGH SOUTH CENTRAL WI AND CENTRAL
LOWER MI.

THEN ON MON, THE IMPRESSIVE WINTER STORM WILL CONTINUE TO PRESS
OFF TO THE NORTH AND EAST AND REACH LOWER MI INTO THE OH VALLEY BY
TUES MORNING. ONCE AGAIN, WIDESPREAD HEAVY SNOWFALL AND EXTENSIVE
ICING WILL BE POSSIBLE. THE INCREASING CONFIDENCE IN WPC QPF AND A
MULTI-MODEL ENSEMBLE APPROACH WITH THERMALS SUGGESTS A VERY NARROW
AXIS OF HEAVY SNOWFALL ACCUMULATIONS FROM NWRN IA/SERN MN THROUGH
NORTH CENTRAL WI INTO THE UP OF MI, WHICH MAY INCLUDE THE MSP/STP
METRO AREA, ESPECIALLY SERN SECTION OF THE TWIN CITIES, IN A HIGH
END EVENT. THE ICING COULD BE A CONSIDERABLE PROBLEM FROM SOUTH
CENTRAL WI AND NORTHERN LOWER MI INTO SERN ONTARIO AND SPILLING
INTO PARTS OF INTERIOR NEW ENGLAND, AS THE SHALLOW COLD AIR MASS
HAS DIFFICULTY ERODING.

FINALLY ON TUES, THE POWERFUL BUT PROGRESSIVE SYSTEM WILL SWEEP UP
INTO THE NERN QUAD OF THE COUNTRY, WITH THE MAIN SURFACE LOW OVER
SOUTHERN QUEBEC GRADUALLY GIVING WAY TO A TRIPLE POINT LOW OVER
MAINE AND NOVA SCOTIA BY WEDNESDAY MORNING. THE BULK OF THE HEAVY
SNOW WILL IMPACT QUEBEC BUT MAY CLIP NORTHERN MAINE, WHILE
DEVELOPING CYCLONIC FLOW ON THE BACKSIDE OF THE SYSTEM COULD START
LAKE EFFECT SNOW DOWNWIND OF THE GREAT LAKES. THE INITIAL SURGE OF
MOISTURE INTO NEW ENGLAND MAY RESULT IN SOME ICING FROM NH UP
THROUGH MAINE UNTIL THE COLD AIR CAN BE SCOURED OUT.

...NORTHWEST INTO NORTHERN INTER-MOUNTAIN WEST...

NOT TO BE OUTDONE AND ON THE HEELS OF THE WINTER STORM EXITING THE
CENTRAL ROCKIES, A CLOSED LOW OVER THE NERN PAC WILL STREAM WAVES
OF UPPER DYNAMICS ALONG WITH A RATHER EXTENDED FETCH OF PAC
MOISTURE INTO THE NWRN QUAD OF THE COUNTRY ON SUN. A POSSIBLE
RIVER OF PAC MOISTURE TRANSPORT WILL
TRANSITION DOWN THE COAST FROM WA TO NORTHERN CA. AS A RESULT,
EXPECT HEAVY OROGRAPHIC SNOWFALL TO OCCUR FROM THE WA
CASCADES/OLYMPICS AND OR CASCADES INTO THE NORTHERN CA MTNS AND
NORTHERN SIERRA, WHILE ACCUMULATIONS SHOULD ALSO STACK UP ACROSS
THE OR BLUE MTNS AND ID BITTERROOTS. THE ONSHORE FETCH INTO THE
PAC NW SHOULD GRADUALLY RELAX SOME ON MON BUT EXPECT SOME
ADDITIONAL ACCUMULATIONS IN THE FAVORED TERRAIN FROM THE NW TO THE
NORTHERN ROCKIES AND INTER-MOUNTAIN WEST. THEN ON TUES, AN
EVOLVING UPPER VORTEX AND TROUGH NEAR THE GULF OF AK/NERN PAC WILL
STEER A RATHER POTENT SHORT WAVE TROUGH WITH A TREMENDOUS FETCH OF
SWRLY UPPER DIFLUENT FLOW AND PAC MOISTURE TRANSPORT INTO THE NW.
SNOW LEVELS MAY INCREASE WITH THIS TYPE OF SYSTEM ARRIVING BUT
HEAVY SNOW SHOULD STILL BE A THREAT FOR THE WA CASCADES INTO THE
BLUE MTNS AND NORTHERN BITTERROOTS.

MUSHER



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