EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 130 AM EST THU FEB 02 2017 VALID 12Z SUN FEB 05 2017 - 12Z THU FEB 09 2017 ...OVERVIEW... THERE ARE SOME THEMES THAT DEVELOPED IN YDAYS 00Z GUIDANCE WHICH CONTINUED INTO THE 12Z/18Z CYCLES. HOWEVER THERE IS STILL A FAIR AMOUNT OF UNCERTAINTY WITH HOW ERN PAC/SWRN CANADA ENERGY WILL ULTIMATELY AMPLIFY INTO THE ERN STATES... SUPPORTING WHAT COULD BE A FAIRLY STRONG SFC SYSTEM ONCE IT REACHES THE GRTLKS/NORTHEAST AND ERN CANADA BY DAYS 6-7 WED-THU. IN SPITE OF THE DETAIL UNCERTAINTIES ALONG THE WAY LATEST GUIDANCE SHOWS BETTER THAN AVG AGREEMENT IN PRINCIPLE FOR THE LARGE SCALE PATTERN FEATURING A DEEP TROUGH OVER THE EAST AND STRONG RIDGE JUST INLAND FROM THE WEST COAST BY NEXT THU. ...GUIDANCE EVALUATION/PREFERENCES... FOR THE OVERALL DAYS 3-7 SUN-THU PERIOD AN AVG OF THE 18Z GFS/GEFS MEAN AND 12Z ECMWF/ECMWF MEAN PROVIDED THE BEST INTERMEDIATE SOLN AMONG LATEST GUIDANCE FOR REPRESENTING CURRENT TRENDS OR CONTINUITY AS APPROPRIATE. PREFS LEANED MORE TOWARD OPERATIONAL GUIDANCE INTO 12Z TUE WITH A MORE EVEN WEIGHTING FOR THE REST OF THE PERIOD. DURING SUN-MON... FOR ABOUT THE PAST DAY GUIDANCE HAS GENERALLY LATCHED ONTO THE IDEA OF A NERN PAC UPR LOW A LITTLE FARTHER OFFSHORE THAN WHAT HAD BEEN FCST IN PRIOR CYCLE(S). IN ADDITION TO YIELDING A FARTHER WWD TRACK FOR A MID-LATITUDE ERN PAC WAVE NOW FCST TO BE JUST OFF THE PAC NW COAST ON SUN... THE CURRENT UPR LOW POSN ALLOWS FOR STRONGER NERN U.S. TROUGHING ALOFT AND ASSOC SFC DEVELOPMENT. FOR BOTH AREAS A COMPROMISE LOOKED REASONABLE FOR RESOLVING DETAIL/POSN DIFFS. CNTRL-ERN U.S. SFC DEVELOPMENT AFTER EARLY MON IS STILL AT THE MERCY OF SMALLER SCALE UNCERTAINTIES AS ENERGY NEAR THE WEST COAST/BC SHEARS INLAND AND AMPLIFIES. AS A RESULT THERE IS STILL FAIRLY BROAD MODEL/ENSEMBLE SPREAD. OF PARTICULAR NOTE THE STARTING BLEND KEPT 18Z GFS WEIGHTING SUFFICIENTLY LOW TO DOWNPLAY ITS FARTHER NWD SFC LOW TRACK THAT WAS ON THE NRN SIDE OF THE ENSEMBLE SPREAD AND PERHAPS EXTENDED TOO FAR INTO THE COLD AIR. THE 12Z UKMET WAS ONE OTHER NRN SOLN. AMONG NEW 00Z RUNS THE GFS/UKMET HAVE NUDGED SWD A BIT BUT ARE STILL NOT AS FAR S AS THE GEFS MEAN. ALSO THE 00Z UKMET/CMC ARE ON THE FAST SIDE OF THE SPREAD. ECMWF RUNS THROUGH 12Z/01 CONTINUED TO BE AMONG THE DEEPEST WITH THE SFC LOW BY WED. BY 12Z DAY 7 THU MOST MODELS/MEANS ARE UNUSUALLY AGREEABLE ALOFT ASIDE FROM DETAILS OVER THE GRTLKS/NORTHEAST AND ERN CANADA... WITH A MEAN TROUGH FROM THE GRTLKS SWD AND THE UPSTREAM RIDGE AROUND 115-120W. THE 12Z GFS/CMC WERE A LITTLE FASTER THAN CONSENSUS WITH AN APPROACHING ERN PAC TROUGH BUT THE NEW 00Z CMC HAS ADJUSTED BACK TO CONSENSUS. ...WEATHER HIGHLIGHTS/THREATS... WWD-FACING TERRAIN ACROSS THE NRN 2/3 OF THE WEST WILL REMAIN THE PROMINENT FOCUS FOR PERIODS OF MDT-HVY PRECIP DURING THE PERIOD. HIGHEST 5-DAY TOTALS SHOULD BE OVER NRN CA AND SIERRA NEVADA RANGE AND LOCATIONS ALONG THE PAC NW COAST/CASCADES. AT LEAST OVER THE WEST COAST STATES SNOW LEVELS SHOULD BE LOWEST EARLY IN THE WEEK AND THEN RISE A BIT BY THU UNDER THE INFLUENCE OF THE ERN PERIPHERY OF A SYSTEM COMING INTO THE PICTURE WELL OFFSHORE. SYSTEM OFF THE PAC NW COAST ON SUN MAY GENERATE A PERIOD OF STRONG WINDS. RECENT TREND TOWARD HIGHER HGTS ALOFT OVER THE WEST LEADS TO AN EXPECTATION OF WARMER TEMPS... ONLY MODESTLY BELOW NORMAL OVER NRN AREAS AND PERHAPS REACHING AT LEAST 10-15F ABOVE NORMAL SRN AREAS BY MIDWEEK. PRECIP HAS TRENDED NOTICEABLY LIGHTER WITH THE SYSTEM AFFECTING THE EAST ON SUN. SOME LGT SNOW IS PSBL OVER THE GRTLKS/CNTRL APLCHNS/NORTHEAST AND LGT RAIN OVER THE SOUTH. AS CNTRL-ERN U.S. LOW PRESSURE DEVELOPS FROM MON ONWARD SNOW SHOULD SPREAD ACROSS THE NRN TIER AND INTO NEW ENGLAND WHILE RAIN INCREASES IN COVERAGE/INTENSITY OVER THE MS VLY/OH VLY REGIONS AND THEN PROGRESSES EWD... WITH A NARROW TRANSITION ZONE OF VARYING PRECIP TYPES BTWN THESE AREAS. A CHANGEOVER IS PSBL AT SOME LOCATIONS AS WELL. CURRENTLY THE BEST POTENTIAL FOR SOME HVY RNFL AND HIGHEST PRECIP TOTALS IS OVER THE TN VLY/OH VLY INTO THE APLCHNS. SOME AREAS MAY SEE STRONG WINDS DEPENDING ON HOW DEEP THE SFC LOW BECOMES. EXPECT A PERIOD OF WELL ABOVE NORMAL TEMPS AHEAD OF THIS SYSTEM CNTRL-SRN AREAS WHILE TRAILING COLDER AIR WILL SPREAD SEWD FROM THE NRN PLAINS TO EAST COAST TUE ONWARD. RAUSCH