EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 147 AM EST TUE JAN 13 2015 VALID 12Z FRI JAN 16 2015 - 12Z TUE JAN 20 2015 ...OVERVIEW... CONFIDENCE IN THE FRI-SUN PART OF THE FCST IS FINALLY INCREASING NOW THAT GUIDANCE IS CLUSTERING BETTER FOR THE EVOLUTION OF SHRTWV ENERGY EXPECTED TO BE ENTERING WRN NOAM NEAR THE START OF THE PERIOD. HOWEVER THE TYPICALLY LOWER PREDICTABILITY OF A PROGRESSIVE/LOW AMPLITUDE PATTERN... SUCH AS THAT IN THE CURRENT FCST FOR MOST OF THE PERIOD... COMES INTO PLAY BY THE FIRST HALF OF NEXT WEEK AS EVIDENCED BY GUIDANCE SPREAD AND CONTINUITY CHANGES IN SOME SOLNS. THE PACIFIC ORIGIN OF FLOW ALOFT SHOULD SUPPORT A PERIOD OF RELATIVELY WARM TEMPS OVER MOST OF THE LOWER 48... AND HEAVIEST PCPN CONCENTRATED FROM THE CNTRL-NRN WEST COAST INTO THE NRN ROCKIES WITH LIMITED COVERAGE/INTENSITY OF PCPN OVER MOST OTHER AREAS. ...GUIDANCE EVALUATION AND PREFERENCES... AFTER MULTIPLE DAYS OF GUIDANCE BEING AT ODDS REGARDING PAC ENERGY REACHING WRN NOAM LATE THIS WEEK AND ITS EVENTUAL DOWNSTREAM EVOLUTION... THE PAST 12-24 HRS OF GFS/GEFS SOLNS HAVE TRENDED TOWARD THE ECMWF CLUSTER THAT HAD SHOWED EARLIER PASSAGE OF ENERGY THROUGH THE INITIAL WRN NOAM MEAN RIDGE AND THEN PROGRESSION OF A TROUGH ACROSS THE NRN HALF OF THE CONUS. EVEN WITH BETTER AGREEMENT IN PRINCIPLE INDIVIDUAL SOLNS STILL DIFFER IN AMPLITUDE AND TIMING OF THE TROUGH WITH THE 12Z ECMWF LEANING A TAD FAST/AMPLIFIED AND LATEST GFS/PARALLEL GFS RUNS SOMEWHAT SLOWER. A COMPROMISE AMONG THE 18Z GEFS/12Z ECMWF MEANS... WITH 2/3 WEIGHTING GIVEN TO THE ECMWF MEAN GIVEN THAT IT HAS BEEN THE APPARENT DESTINATION OF RECENT GFS/GEFS TRENDS... PROVIDES THE BEST INTERMEDIATE SOLN AMONG OPERATIONAL SOLNS FOR DAYS 3-5 FRI-SUN. MINOR MANUAL ENHANCEMENTS WERE MADE IN THE SFC FCST WHERE SUFFICIENT MODEL CONSENSUS EXISTS. FROM NEAR THE WEST COAST ON SUN AND DOWNSTREAM THEREAFTER THE PAST 12-24 HRS OF MODEL/ENSEMBLE GUIDANCE HAS MADE SOME SIGNIFICANT ADJUSTMENTS IN SHRTWV EMPHASIS. SPECIFICALLY THE SHRTWV EXPECTED TO BE NEAR THE WEST COAST AS OF EARLY SUN HAS NOW TRENDED MUCH FLATTER SO THAT AN AREA OF SFC LOW PRESSURE THAT HAD BEEN DEPICTED FROM THE PLAINS INTO THE MIDWEST IS MUCH WEAKER IF EXISTING AT ALL. UPSTREAM ENERGY IS THEN FCST TO BEGIN AMPLIFYING NEAR OR INLAND FROM THE WEST COAST IN RESPONSE TO A BUILDING ERN PAC RIDGE. THIS LATTER TROUGH SHOWS GREATER THAN AVG CONTINUITY IN DEPTH/LONGITUDE AMONG RECENT ECMWF MEANS WHILE GEFS MEANS HAVE BEEN TRENDING FASTER. THE DEEP/CLOSED SOLN OF THE 12Z ECMWF IS FAIRLY EXTREME RELATIVE TO THE FULL ENSEMBLE SPREAD BUT NOT AN OUTLIER. TELECONNECTIONS RELATIVE TO THE POSITIVE HGT ANOMALY CENTER THAT DEVELOPS OVER THE ERN PAC BY THE D+8 TIME FRAME SUPPORT A TROUGH THAT IS FAIRLY WELL INLAND. THE ECMWF MEAN COULD STILL BE PLAUSIBLE GIVEN SUFFICIENT PROGRESSION AFTER DAY 7 BUT ENOUGH UNCERTAINTY EXISTS TO FAVOR ADJUSTING THE 70 PCT ECMWF MEAN WEIGHTING THROUGH DAY 5 GRADUALLY BACK TO 50 PCT BY DAY 7 TUE. ...SENSIBLE WEATHER HIGHLIGHTS... THE PRIMARY FOCUS FOR HVY RNFL AND HIGH ELEV SNOW SHOULD BE FROM THE PAC NW/NRN CA COAST INTO THE NRN ROCKIES... WITH ACTIVITY LIKELY TRENDING SOMEWHAT LIGHTER BY NEXT MON-TUE AS TERRAIN-FOCUSING WESTERLY FLOW ALOFT SHOULD BECOME MORE AMPLIFIED. NARROW BAND OF MSTR ORIGINATING FROM MID-LWR LATITUDES OF THE PAC/ANOMALOUSLY HIGH PWATS REACHING THE PAC NW COAST MAINTAIN REASONABLE CONFIDENCE IN THIS EVENT. RECENT GUIDANCE TRENDS TOWARD FLATTER SHRTWV ENERGY ENTERING THE WEST AROUND DAY 5 SUN LEAD TO LESSER EXTENT OF MEASURABLE PCPN SWD FROM THE MOST FAVORED AREA. THE REMAINDER OF THE CONUS SHOULD SEE BELOW AVG COVERAGE/INTENSITY OF PCPN DURING THE PERIOD. LOCATIONS FROM THE EXTREME NRN TIER ACROSS THE GRTLKS/NRN NEW ENGLAND MAY SEE ONE OR MORE EPISODES OF MOSTLY LGT SNOW/MIX... WHILE LATE IN THE FCST A LITTLE MSTR MAY TRY TO LIFT NWD FROM THE GULF OF MEXICO BUT DUE TO CHANGES ALOFT THIS EVOLUTION IS DELAYED COMPARED TO FCSTS FROM 12-24 HRS AGO. EXPECT ABOVE NORMAL TEMPS TO PREVAIL ACROSS THE LOWER 48 ASIDE FROM A CHILLY FRI ALONG THE EAST COAST... WITH GREATEST ANOMALIES OF PLUS 10-20F OR HIGHER OVER THE NRN TIER STATES. LOCATIONS FROM THE GRTBASIN INTO THE CNTRL PLAINS MAY ALSO SEE SOME PLUS 10-15F ANOMALIES ON ONE OR MORE DAYS. ON AVG THE MIN TEMPS SHOULD BE A LITTLE FARTHER ABOVE NORMAL THAN DAYTIME HIGHS. RAUSCH