EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 238 AM EDT SUN OCT 09 2016 VALID 12Z WED OCT 12 2016 - 12Z SUN OCT 16 2016 ...PATTERN OVERVIEW... GUIDANCE MAINTAINS GOOD AGREEMENT AND CONTINUITY IN DEPICTING THE ESTABLISHMENT OF AN ERN PACIFIC MEAN TROUGH ALOFT THAT WILL PROMOTE A MULTI-DAY PERIOD OF ENHANCED PCPN FROM THE CNTRL-NRN WEST COAST INTO THE NRN ROCKIES... WITH LOW AMPLITUDE MEAN FLOW PREVAILING ACROSS MUCH OF THE LOWER 48. PRIMARY UNCERTAINTIES IN THE FCST INVOLVE SPECIFICS OF SHRTWV ENERGY ENTERING THE WEST EARLY IN THE PERIOD AND CONTINUING ACROSS THE CONUS THEREAFTER FOLLOWED BY ERN PAC-WRN U.S. DETAILS SFC/ALOFT LATE IN THE PERIOD. ...GUIDANCE EVALUATION... THE UPDATED FCST INCORPORATES THE MOST COMMON ASPECTS OF THE 18Z GFS/12Z ECMWF AND THEIR ENSEMBLE MEANS WITH MORE OPERATIONAL MODEL EMPHASIS DAYS 3-4 WED-THU AND MORE ENSEMBLE MEAN WEIGHTING LATE. DAY 7 SUN USES THE MEANS EXCLUSIVELY. THE RESULTING BLEND YIELDS SOME DETAIL REFINEMENTS WHILE MAINTAINING FAIRLY GOOD CONTINUITY OVERALL. THERE IS STILL A FAIR AMOUNT OF UNCERTAINTY REGARDING DETAILS OF DIFFUSE SHRTWV ENERGY ENTERING THE WEST WED-THU AND CONTINUING EWD THEREAFTER. HOW THIS SHRTWV EVOLVES WILL DETERMINE COVERAGE/INTENSITY OF PCPN FROM THE PLAINS EWD. CURRENT OR RECENT GFS/ECMWF/CMC RUNS HAVE ALL SHOWN POTENTIAL FOR ENERGY IN THE SRN PART OF THE SHRTWV TO SEPARATE SOMEWHERE BTWN THE SWRN U.S./NWRN MEXICO AND THE SRN PLAINS. THE FULL RANGE OF GUIDANCE SUGGESTS THE 12Z/18Z GFS RUNS MAY PULL OFF THE SRN ENERGY TOO FAR WWD... AND INDEED THE NEW 00Z GFS HAS ADJUSTED EWD. INTERESTINGLY THE 00Z GFS ENDS UP NOT FAR FROM THE 00Z/08 ECMWF BUT THE 12Z RUN IS AMONG THE FASTEST SOLNS. REMAINING 00Z GUIDANCE THUS FAR SUPPORTS FASTER PROGRESSION AND LESS SEPARATION CLOSER TO THE 12Z ECMWF SCENARIO. OVER THE ERN PAC/WRN U.S. THE FCST LOOKS FAIRLY GOOD INTO DAY 5 FRI. THE DOMINANT FEATURE WILL BE A DEEP SFC LOW FCST TO EVOLVE TO THE W OF VANCOUVER ISLAND WITH SOME FINER DETAILS OF TRACK/TIMING/DEPTH YET TO BE DETERMINED. BY DAYS 6-7 SAT-SUN THE 12Z/18Z GFS RUNS FLATTEN THE ERN PAC TROUGH AND SEND MORE ENERGY INTO THE WEST COMPARED TO OTHER GUIDANCE INCLUDING RECENT GEFS MEANS. THIS LEADS TO THOSE GFS RUNS HAVING A SFC LOW TRACK INTO OREGON AND SPREADING MSTR FARTHER SEWD ACROSS THE WEST. AN OVERWHELMING MAJORITY OF MODEL/ENSEMBLE SOLNS KEEP ANY SFC LOWS OFFSHORE. EVEN WITH THE QUESTIONABLE LEADING SYSTEM IN THE 12Z/18Z GFS... THE GFS RUNS AND 12Z ECMWF AGREE ON THE EXISTENCE OF ANOTHER STRONG SFC LOW JUST OFFSHORE THE PAC NW DAY 7 SUN. THE 00Z GFS COMPARES BETTER TO THE PREFERRED MEANS LATE IN THE PERIOD. ...WEATHER HIGHLIGHTS/THREATS... MSTR APPEARS TO BE ON TRACK TO REACH THE PAC NW AROUND WED NIGHT-THU. EXPECT PCPN OF VARYING INTENSITY TO PERSIST THROUGH AND BEYOND NEXT WEEKEND FROM THE CNTRL-NRN WEST COAST INTO NRN ROCKIES. FAVORED LOCATIONS FROM THE NRN CA COAST NWD INTO THE PAC NW SHOULD SEE HIGHEST TOTALS WHICH COULD REACH OR EXCEED 5-10 INCHES. PARTS OF THE NORTHWEST WILL ALSO LIKELY SEE PERIODS OF STRONGER WINDS FROM THU ONWARD WITH SPECIFICS DETERMINED BY EVOLUTION OF ONE OR MORE POTENTIALLY STRONG ERN PAC SYSTEMS. MEANWHILE A COLD FRONT PUSHING SEWD FROM THE GRTLKS-PLAINS WED ONWARD WILL BE ACCOMPANIED BY AREAS OF RNFL THAT SHOULD DECREASE IN COVERAGE/INTENSITY AS THE FRONT REACHES THE ERN STATES. SHRTWV ENERGY ENTERING THE WEST AROUND MIDWEEK WILL GENERATE ANOTHER AREA OF RAIN OVER THE PLAINS/MS VLY BY THU-FRI. UNCERTAINTY IN SPECIFICS ALOFT... AND CONSENSUS FCST FOR FAIRLY STRONG SFC HIGH PRESSURE OVER THE ERN STATES... LOWER CONFIDENCE IN DETERMINING HOW MUCH MSTR WILL ULTIMATELY EXTEND INTO THE APLCHNS/MID ATLC BY FRI NIGHT-SAT. A SYSTEM ALONG/N OF THE CANADIAN BORDER MAY BRING SOME LGT PCPN INTO THE GRTLKS LATE IN THE PERIOD. LGT NELY LOW LVL FLOW MAY BRING PERIODS OF LGT RAIN TO PARTS OF THE FLORIDA PENINSULA. CHILLY HIGH PRESSURE BUILDING INTO THE PLAINS/MS VLY EARLY IN THE PERIOD WILL SUPPORT HIGHS OF 10-20F BELOW NORMAL OVER THE NRN-CNTRL PLAINS ON WED. BY THE LATTER HALF OF THE PERIOD THE WEST COAST STATES/NRN ROCKIES SHOULD SEE BELOW NORMAL HIGHS WITH PERSISTENT CLOUDS/PCPN AND COOL HIGH PRESSURE SHOULD KEEP THE NRN 2/3 OF THE EAST NEAR TO SLIGHTLY BELOW NORMAL. ELSEWHERE BY NEXT WEEKEND EXPECT A FAIRLY BROAD AREA OF ABOVE NORMAL READINGS FOR BOTH MIN AND MAX TEMPS. RAUSCH