EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 115 AM EST THU JAN 26 2017 VALID 12Z SUN JAN 29 2017 - 12Z THU FEB 02 2017 ...OVERVIEW AND GUIDANCE EVALUATION... THE WRN RIDGE/ERN TROUGH MEAN PATTERN SHOULD BECOME SOMEWHAT WEAKER AND BROADER WITH TIME WHILE A LARGE ERN PAC SYSTEM ASSOC WITH A SLOW MOVING CLOSED LOW APPROACHES THE WEST COAST. WITHIN THE AGREEABLE MEAN PATTERN THERE IS STILL SIGNIFICANT SPREAD FOR SHRTWV DETAILS MON ONWARD... ORIGINATING FROM NERN PAC ENERGY ROUNDING THE WRN RIDGE EARLY IN THE PERIOD. COMPLEXITIES OF NERN PAC/ALASKA FLOW TOWARD TUE-THU BEGIN TO ADD SOME UNCERTAINTY FOR THE ERN PAC SYSTEM WHILE SOLNS REMAIN QUITE VARIED FOR TROUGH/UPR LOW ENERGY ACROSS NRN MEXICO. IT REMAINS DIFFICULT TO HAVE A LOT OF CONFIDENCE IN ONE OR TWO SPECIFIC SOLNS FOR ALL FEATURES OF INTEREST... LEADING TO PREFERRING VARIOUS WEIGHTS OF THE 18Z GFS/GEFS MEAN AND 12Z ECMWF/ECMWF MEAN AS THE BEST STARTING POINT FOR THE OVERALL FCST. FOR THE NERN PAC ENERGY ULTIMATELY FLOWING INTO THE ERN U.S. MEAN TROUGH... THE GFS/GEFS MEAN RUNS CONTINUE TO SHOW MORE AMPLITUDE THAN MOST OTHER SOLNS. THIS RELATIONSHIP HAS EXISTED FOR MULTIPLE RUNS WITH NO APPARENT TRENDING BY EITHER CLUSTER SO PREFER TO STAY FAIRLY CLOSE TO THE MIDDLE OF THE GUIDANCE SPREAD. AT THE LEADING EDGE OF DYNAMICS ALOFT THERE REMAINS DECENT AGREEMENT IN PRINCIPLE FOR A FAIRLY VIGOROUS SYSTEM REACHING THE VICINITY OF THE UPR GRTLKS AROUND DAY 5 TUE AND CONTINUING ONWARD THEREAFTER. HOWEVER THERE IS STILL A LOT OF MODEL/ENSEMBLE SPREAD FOR SFC DETAILS. THE NEW 00Z GFS HAS ONE OF THE DEEPEST SOLNS AMONG RECENT RUNS WHILE THE PAST COUPLE ECMWF RUNS THROUGH THE 12Z CYCLE HAVE SHOWN MORE EMPHASIS ON LOW PRES FARTHER NWD. THE 00Z CMC IS ON THE SRN SIDE OF THE SPREAD AND THE 00Z UKMET FARTHER NWD SO THERE ARE STILL MORE QUESTIONS THAN ANSWERS. ENSEMBLE MEANS MAINTAIN A TRACK ACROSS THE UPR GRTLKS. WITH THE LARGE SYSTEM DRIFTING TOWARD THE WEST COAST THE 12Z ECMWF MEAN APPEARED TO BE THE LESS OPTIMAL SOLN AS IT WAS ON THE LEADING SIDE OF GUIDANCE ON MOST DAYS FROM MON ONWARD. THEN BY TUE-THU THE NERN PAC TO BERING SEA PATTERN INCREASES IN COMPLEXITY AS AN UPR HIGH MAY CLOSE OFF BRIEFLY BEFORE A STRONGER RIDGE/PSBL CLOSED HIGH BUILDS OVER THE ERN BERING SEA/WRN-NRN ALASKA. UNCERTAINTY OVER THE SHAPE OF THESE RIDGES TENDS TO LOWER THE PREDICTABILITY FOR FLOW TO THE S/E. BY LATE IN THE PERIOD THE 12Z GFS WAS LEAST PREFERRED AS ITS INTERACTIONS LED TO FASTER ERN PAC SYSTEM PROGRESSION THAN OTHER SOLNS. SOLNS INCREASINGLY DIVERGE FOR NRN MEXICO ENERGY THAT SHOULD BE IN THE FORM OF A CLOSED LOW FOR AT LEAST A PORTION OF THE FCST PERIOD. FOR THE PAST DAY GFS RUNS HAVE BECOME QUITE OPEN/FAST WITH THE SHRTWV WHILE THE 12Z ECMWF WAS THE SLOWEST WITH A CLOSED LOW. THE ONLY COMMON ELEMENT IN NEW 00Z GUIDANCE THUS FAR IS FASTER PROGRESSION THAN THE 12Z ECMWF. ...WEATHER HIGHLIGHTS/THREATS... OVER THE WEST... EXPECT A LITTLE LGT PCPN OVER THE PAC NW WITH A FRONT ON SUN. THE FRONT SHOULD BECOME DRAPED OVER NRN AREAS AND MAY SERVE AS A FOCUS FOR SOME ADDITIONAL PCPN LATER IN THE PERIOD WITH THE ARRIVAL OF PACIFIC MSTR. AS THE LARGE ERN PAC SYSTEM APPROACHES EXPECT RAIN AND HIGHER ELEV SNOW TO INCREASE IN COVERAGE AND INTENSITY ALONG THE THE NRN 2/3 TO 3/4 OF THE WEST COAST AROUND MIDWEEK. FOR THE 5-DAY PERIOD HIGHEST TOTALS ARE MOST LIKELY TO BE OVER NRN CA/SWRN OR AND OVER THE OLYMPICS/VANCOUVER ISLAND. COOL TEMPS LATE IN THE WEEKEND SHOULD TREND TOWARD NEAR OR MODESTLY ABOVE NORMAL OVER THE SRN 2/3 OF THE REGION WHILE NRN AREAS SHOULD REMAIN SLIGHTLY BELOW NORMAL. TO THE E OF THE ROCKIES... THERE WILL BE ONE EPISODE OF LAKE EFFECT SNOW SUN INTO MON. THEN THE SYSTEM TRACKING INTO THE GRTLKS BY TUE SHOULD BRING AN AREA OF SYNOPTIC SCALE SNOW FROM THE NRN TIER INTO THE NORTHEAST BUT DETAILS OF THIS SYSTEM REMAIN TOO UNCERTAIN TO PINPOINT INTENSITY AND LOCATION OF HIGHEST AMTS. ANOTHER PERIOD OF LAKE EFFECT SNOW WILL LIKELY COMMENCE AS THIS SYSTEM DEPARTS. THE FL PENINSULA MAY SEE SOME LGT RNFL ON SUN. THE RNFL FCST ACROSS SRN TX IS VERY UNCERTAIN WITH DEPENDENCE ON THE FORM/TIMING OF UPR LVL ENERGY CROSSING NRN MEXICO. MOST LIKELY SCENARIO AT THIS TIME LIES BTWN THE WET ECMWF AND RELATIVELY DRY GFS. EXPECT TEMPS TO AVERAGE BELOW NORMAL OVER THE EAST THOUGH WITH A BRIEF WARMUP AROUND TUE-WED. THE PLAINS SHOULD SEE ABOVE NORMAL TEMPS FOR THE PERIOD AS A WHOLE. HOWEVER THE NRN PLAINS MAY SEE BELOW NORMAL HIGHS BY WED OR THU AFTER A WARM START TO THE PERIOD... ESPECIALLY WITH RESPECT TO MINS THAT MAY BE 20F OR MORE ABOVE NORMAL SUN-TUE. RAUSCH