Quantitative Precipitation Forecast
Issued by NWS

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000 FOUS11 KWBC 180918 QPFHSD PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 418 AM EST THU DEC 18 2014 VALID 12Z THU DEC 18 2014 - 12Z SUN DEC 21 2014 ...WESTERN U.S.... SNOWS ARE EXPECTED TO DEVELOP IN HIGHER ELEVATIONS OF THE PACIFIC NORTHWEST AND NORTHERN ROCKIES LATER TONIGHT AND EARLY FRIDAY AS A WELL DEFINED UPPER TROUGH APPROACHES AND ASCENT GETS GENERATED BY AN UPPER LEVEL JET STREAK IN ADVANCE OF THE LOW. THIS INDUCES UPPER DIVERGENCE/LOWER CONVERGENCE MAXIMA PEAKING OVER WASHINGTON BEFORE WEAKENING AS IT MOVES INLAND OVER THE NORTHERN ROCKIES. LIKEWISE...SNOWS OCCURS OVER HIGHER ELEVATIONS OF THE OR/NORTHERN CA RANGES AS A JET MAX ROUNDS THE BASE OF THE TROUGH AND UPPER DIVERGENCE AIDS UPSLOPE FLOW IN PRODUCING ASCENT...LIKELY RESULTING IN SEVERAL INCHES AT HIGHER ELEVATIONS. FROM LATE FRIDAY THROUGH SATURDAY...THE MODELS/ENSEMBLES SHOW A WELL DEFINED UPPER JET MAXIMA MOVING WEST TO EAST FROM THE NORTHEAST PACIFIC AND EVENTUALLY INTO OR SAT. HIGHER AMOUNTS ARE EXPECTED IN THE WA CASCADES AS WELL DEFINED UPPER DIVERGENCE MAXIMA OCCUR INT HE LEFT EXIT REGION OF THE UPPER JET. THE GFS AND EC STILL DEPICT 850-700 MB MOISTURE FLUXES INCREASING TO 3-4 STANDARD DEVIATIONS ABOVE NORMAL IN WESTERN OR. THE UNCERTAINTY RELATES TO QPF AMOUNTS WHILE IN THE FORM OF SNOW. THE MODELS SHOW RAPID WARMING AS STRONG LOW LEVEL SOUTHWEST FLOW PRODUCES WARMING TEMPERATURES...WITH RAPIDLY RISING SNOW LEVELS AS A RESULT. BY SATURDAY...THOUGH...HEIGHTS COME DOWN ENOUGH WHERE THE AREAL COVERAGE OF SNOW AND AMOUNTS INCREASE QUITE A BIT WHEN COMPARED WITH DAYS 1/2 ACROSS PARTS OF THE PAC NW. ...CENTRAL PLAINS DAY 1... A 700 MB WAVE WITH A POSSIBLE CLOSED CIRCULATION WILL CONTINUE TO MOVE FROM NEB/KS EASTWARD INTO PARTS OF MO. WHILE SOME ADDITIONAL LIGHT SNOWFALL AMOUNTS ARE POSSIBLE IN THIS AREA AFTER 12Z THIS MORNING...WITH A FEW PLACES IN NORTHEAST KS AND ADJOINING AREAS MAY SEE ANOTHER INCH OR TWO...THE WINDOW OF OPPORTUNITY TO ACCUMULATE AN ADDITIONAL 4 INCHES OF SNOW IS QUITE SHORT. FREEZING PCPN WILL BE ISOLATED IN NATURE AND QUITE LIGHT. CONSEQUENTLY...NO AREAS FOR SNOW OR ICING DEPICTED HERE. ...NORTHEAST DAY 1... A LOW AT THE SURFACE AS WELL AS IN THE LOW/MID LEVELS WILL CONTINUE TO PULL AWAY FROM NEW ENGLAND. DESPITE WEAKENING MESOSCALE FORCING...SOME LIGHT SNOW SHOULD CONTINUE ACROSS PARTS OF NORTHERN/WESTERN ME TODAY AS NORTHERLY LOW LEVEL WINDS FORCES COLD AIR WITH HI RH UPSLOPES. THERE WAS ENOUGH ENSEMBLE AND OPERATIONAL MODEL SUPPORT FOR A SLIGHT RISK OF 4 INCHES TO CONTINUE INTO THE DAY TODAY ACROSS NORTHERN ME. THIS ALSO HAPPENS TO BE THE AREA WHERE TEMPERATURES REMAIN COLD ENOUGH TO SNOW ALL DAY . THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. BANN $$

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