EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1100 AM EST SAT JAN 31 2015 VALID 12Z TUE FEB 03 2015 - 12Z SAT FEB 07 2015 ...OVERVIEW AND PREFERENCES... MODEL AND ENSEMBLE GUIDANCE MAINTAINS UNUSUALLY GOOD AGREEMENT AND CONTINUITY FOR THE EXPECTED LARGE SCALE FLOW INTO NEXT WEEKEND. CONUS TROUGHING WILL AMPLIFY DURING THE FIRST HALF OF THE PERIOD AS A BUILDING/SHARPENING RIDGE APPROACHES AND CROSSES THE WEST COAST. THE ERN PAC TROUGH/WRN RIDGE/ERN TROUGH PATTERN SHOULD BROADEN SOMEWHAT BY LATE NEXT WEEK BUT REMAIN FAIRLY AMPLIFIED. TO RESOLVE LINGERING DETAIL QUESTIONS WITHIN THE AGREED UPON MEAN FLOW PREFER TO START WITH A GENERAL MODEL/ENSEMBLE MEAN BLEND AMONG 00Z/06Z SOLNS... A TAD MORE TOWARD THE 00Z ECMWF/ECMWF MEAN RELATIVE TO THE 00Z-06Z GFS/06Z GEFS MEAN. ...GUIDANCE EVALUATION... MULTIPLE UNCERTAINTIES PERSIST WITHIN AND ON THE SRN PERIPHERY OF THE MEAN TROUGH ALOFT FCST TO EVOLVE OVER THE ERN HALF OF THE CONUS. THERE ARE SOME TIMING DIFFS WITH THE ENERGETIC SHRTWV PROGRESSING FROM THE NRN PLAINS THROUGH THE NORTHEAST WED-THU. MODELS SUGGEST THAT SFC LOW PRES NORTHEAST OF MAINE LIKELY MORE SIGNIFICANT FROM THE PERSPECTIVE OF PCPN COVERAGE/TYPE WOULD BE THE COMBINED ISSUES INVOLVING WEAK ERN PAC ENERGY FCST TO AMPLIFY TOWARD THE SERN STATES... AND A LEADING UPR LOW EJECTING FROM MEXICO. THERE IS STILL SIGNIFICANT MODEL/ENSEMBLE SPREAD WITH THE TRACK/TIMING OF ONE OR MORE ASSOC SFC WAVES FROM THE GULF OF MEXICO NEWD INTO THE WRN ATLC. THE 00Z UKMET IS CURRENTLY THE MOST NWWD EXTREME FOR THE SFC SYSTEM AND NEAR THE NWRN FRINGE OF THE ENSEMBLE ENVELOPE. THE 00Z-06Z GFS/00Z CMC ARE ALSO A BIT NWD/NWWD OF THE GUIDANCE AVG BUT AT LEAST THE LATEST GFS RUNS HAVE TRENDED SUFFICIENTLY SLOWER TO ACHIEVE TIMING SIMILAR THE PAST COUPLE ECMWF RUNS. GIVEN THE POSN OF THE EJECTING UPR LOW AS OF EARLY DAY 4 WED THERE SEEMS TO BE REASONABLE SUPPORT A SFC WAVE FORMING OVER THE WRN GULF ON WED... WITH NRN STREAM FLOW DETAILS BECOMING IMPORTANT THEREAFTER. NOTE THAT THE 06Z GFS/00Z CMC MAY BE OVERDONE WITH AMPLITUDE OF THE APPROACHING NRN STREAM SHRTWV. BY LATE IN THE PERIOD DIFFS IN THE DETAILS OF FLOW ACROSS SRN CANADA AND THE NRN TIER CONUS IMPACT THE POSN OF A PSBL FRONTAL BOUNDARY AFFECTING PARTS OF THE NRN CONUS. INSTABILITY OF OPERATIONAL MODEL RUNS ARGUES FOR LEANING A LITTLE CLOSER TO THE ENSEMBLE MEANS FOR THIS PART OF THE FCST BUT 06Z GEFS MEAN TRENDS OFFER MODEST SUPPORT INCLUDING SOME OF LATEST OPERATIONAL RUNS THAT PUSH THE FRONT/TRAILING SFC RIDGE SOMEWHAT FARTHER S INTO THE UPR MIDWEST/UPR GRTLKS BY NEXT SAT. ALONG AND JUST INLAND FROM THE WEST COAST... ONE OR MORE SHRTWVS HEADING INTO/AROUND/THROUGH THE MEAN RIDGE ARE OF SUFFICIENTLY SMALL SCALE TO HAVE LOW CONFIDENCE IN THEIR SPECIFICS. THE ONE NOTABLE ATTRIBUTE OF THE PREFERRED BLEND IS TO DOWNPLAY RECENT GFS RUNS... ESP THE 00Z VERSION... WHICH ARE SOMEWHAT STRONGER WITH ENERGY CROSSING THE WEST. ...SENSIBLE WEATHER HIGHLIGHTS... AREAS FROM THE CNTRL-NRN WEST COAST INTO THE ROCKIES SHOULD SEE TWO FAVORED PERIODS OF PCPN... ONE TUE-WED WITH PRIMARILY LGT-MDT AMTS AND A SECOND LIKELY HEAVIER EVENT CONFINED TO AREAS FROM NRN CA/PAC NW INTO THE NRN ROCKIES. THE LATTER EVENT SHOULD HAVE SOME MSTR SOURCE FROM LOW LATITUDES OF THE PAC HELPING TO ENHANCE PCPN POTENTIAL THOUGH THE AXIS OF BEST DEEP MSTR MAY BE FAIRLY NARROW WITH SHRTWV DETAILS HAVING SIGNIFICANT IMPACT ON TIMING/DURATION OF ENHANCED ACTIVITY. FARTHER EWD THE COMBINATION OF THE UPR LOW EJECTING FROM MEXICO AND NRN STREAM ENERGY EVENTUALLY REACHING THE SERN STATES SHOULD SUPPORT POTENTIAL FOR ENHANCED RNFL ALONG MOST OF THE GULF COAST. PSBL COVERAGE FARTHER NWD... AND POTENTIAL PTYPE ISSUES... IS MUCH MORE UNCERTAIN AND WILL TAKE FURTHER TIME TO RESOLVE. NRN LOCATIONS SHOULD SEE ONE OR TWO AREAS OF SNOW PASS THROUGH DURING THE PERIOD WHILE SOME LAKE EFFECT ACTIVITY IS ALSO PSBL. FOR TEMPS... PARTS OF THE NRN-CNTRL PLAINS SHOULD BE SOMEWHAT BELOW NORMAL FOR A DAY OR TWO EARLY IN THE PERIOD BUT OTHERWISE THE WRN-CNTRL STATES SHOULD BE QUITE WARM WITH SOME PLUS 20-30F ANOMALIES OVER PARTS OF THE PLAINS BY FRI-SAT. PLUS 10-20F ANOMALIES SHOULD PREVAIL OVER THE INTERIOR WEST. ONE CHILLY AIRMASS WITH MINUS 10-20F ANOMALIES WILL DEPART FROM THE NORTHEAST TUE AND THEN ANOTHER COOL SPELL OF SIMILAR DEGREE SHOULD CROSS THE EAST LATER IN THE WEEK. RAUSCH