EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1156 AM EDT TUE SEP 09 2014 VALID 12Z FRI SEP 12 2014 - 12Z TUE SEP 16 2014 ...PATTERN OVERVIEW... GUIDANCE AGREES FAIRLY WELL THAT AN AMPLIFYING ERN PAC TROUGH AND WEST COAST RIDGE DRIFTING INTO WRN NOAM WILL SUPPORT TROUGHING OVER THE ERN HALF OF NOAM. THIS PATTERN... MORE TYPICAL OF THE COLD SEASON THAN LATE SUMMER OR EARLY FALL... SHOULD YIELD BELOW TO MUCH BELOW NORMAL TEMPS OVER MOST OF THE ERN 2/3 OF THE CONUS. THIS AMPLIFIED LARGE SCALE PATTERN SHOULD HAVE ABOVE AVERAGE PREDICTABILITY BUT THERE ARE EMBEDDED INTERMEDIATE TO SMALLER SCALE FEATURES THAT PRESENT SOMEWHAT GREATER UNCERTAINTY. ...GUIDANCE EVALUATION/PREFERENCES... DURING THE FIRST HALF OF THE PERIOD THE PRIMARY FCST ISSUE INVOLVES THE SHRTWV PROGRESSING EWD/NEWD FROM THE NRN HALF OF THE PLAINS AND ASSOC SFC REFLECTION. OVER THE PAST 12-24 HRS MOST GUIDANCE IS SHOWING A FAIRLY CONCENTRATED UPR FEATURE WITH THE PAST TWO ECMWF RUNS AND 00Z UKMET/CMC/ECMWF MEAN ALL SHOWING A WELL DEFINED SFC SYSTEM TRACKING FROM THE GRTLKS INTO QUEBEC DURING SAT-SUN. 00Z/06Z GFS RUNS ARE FASTER THAN THIS PRIMARY CLUSTER WITH THE SHRTWV DUE IN PART TO FASTER PROGRESSION OF A TROUGH OVER CNTRL CANADA. GFS HANDLING OF THE SHRTWV ALOFT LEADS TO MINIMAL INLAND SFC DEVELOPMENT IN ITS FCST. AT THIS TIME THERE APPEARS TO BE SUFFICIENT SUPPORT FOR ADJUSTING CONTINUITY TOWARD THE ECMWF CLUSTER SO INTO EARLY DAY 5 SUN THE FCST IS BASED ON A BLEND OF THE 00Z ECMWF/ECMWF MEAN. FROM LATE DAY 5 THROUGH DAY 7 TUE THERE ARE COMBINED UNCERTAINTIES OF A COMPACT UPR LOW/TROUGH THAT MAY MOVE INTO THE NWRN STATES AS WELL AS SHRTWV/AMPLITUDE DETAILS WITH THE MEAN TROUGH DOWNSTREAM. FOR NOW PREFER TO LEAN TOWARD THE 06Z GEFS/00Z ECMWF MEANS. THE 00Z ECMWF MAY BE TOO AGGRESSIVE IN BREAKING DOWN THE WRN RIDGE AND CONFIDENCE IS TOO LOW IN REMAINING OPERATIONAL SOLNS FOR THE INCOMING ERN PAC FEATURE. FARTHER EWD THE 00Z ECMWF EVOLUTION OVER THE NORTHWEST LEADS TO FLATTER THAN CONSENSUS TROUGHING OVER THE EAST WHILE THE 00Z-06Z GFS/00Z CMC DEVELOP MORE EWD/SEWD AMPLITUDE TO THE TROUGH THAN OTHER SOLNS WHICH IS AN OCCASIONAL BIAS OF THOSE MODELS. IN ADDITION SHRTWV DETAILS BECOME SUFFICIENTLY UNCERTAIN TO RECOMMEND DOWNPLAYING ANY PARTICULAR OPERATIONAL SOLN FOR WAVINESS ALONG THE SLOW MOVING/STNRY FRONTAL BNDRY NEAR THE EAST COAST. GUIDANCE IS SHOWING ANOTHER ERN PAC TROPICAL SYSTEM TRACKING OFFSHORE BAJA CALIF. 00Z/06Z GFS RUNS ARE CURRENTLY FARTHEST NWD WITH THIS FEATURE DUE TO A WEAKER RIDGE ALOFT TO THE N. CONSULT THE FINAL SFC ISSUANCE BY 19Z FOR TODAYS NHC/WPC COORDINATED TRACK. ...SENSIBLE WEATHER HIGHLIGHTS... EARLY IN THE PERIOD EXPECT A PERIOD OF UPSLOPE FLOW ALONG THE ERN SLOPES OF THE SRN HALF OF THE ROCKIES... TO THE S OF A STRONG SFC HIGH THAT SHOULD BE IN THE MID 1030'S MB AS OF EARLY FRI. PSBL SNOW IN THE SHORT RANGE PERIOD WILL LIKELY TAPER OFF EARLY IN THE MEDIUM RANGE BUT MAX TEMPS MAY BE 20-30F BELOW NORMAL FROM PARTS OF THE ERN SLOPES OF THE ROCKIES/HIGH PLAINS INTO THE NERN PLAINS ON FRI WITH A FAIRLY BROAD AREA OF 10-20F BELOW NORMAL READINGS EXTENDING INTO SAT. AT SOME LOCATIONS FRI HIGHS MAY BE CLOSE TO CALENDAR DAY RECORDS FOR COOLEST MAX TEMP. CNTRL-ERN STATES SHOULD REMAIN COOL SUN-TUE BUT MORE IN THE MINUS 5-12F RANGE. EXPECT PCPN TO ACCOMPANY THE LEADING COLD FRONT AND PSBL GRTLKS/QUEBEC SYSTEM. SLOWEST FRONTAL PROGRESSION/WAVINESS MAY ALLOW FOR SOME ENHANCEMENT OR REPEAT ACTIVITY OVER PARTS OF THE MID ATLC/SOUTHEAST. IT WILL LIKELY TAKE SOME TIME TO RESOLVE PRECISE DETAILS OVER THAT REGION DUE TO TYPICALLY LOW PREDICTABILITY OF IMPORTANT SMALLER SCALE SHRTWV DETAILS. OVER THE WEST... THE RIDGE ALOFT BUILDING INTO THE REGION SHOULD SUPPORT ABOVE NORMAL TEMPS MOST DAYS WITH HIGHEST ANOMALIES OF PLUS 10-15F AT SOME LOCATIONS WITHIN WA/OR/ID AND EXTENDING INTO WRN MT BY DAY 7 TUE. NEAR THE END OF THE PERIOD LOCATIONS OVER THE SOUTHWEST WILL NEED TO MONITOR THE POTENTIAL FOR ERN PAC TROPICAL MSTR TO APPROACH THE REGION. BY DAY 7 TUE SOLNS VARY WIDELY WITH IMPORTANT DETAILS ALOFT SO CONFIDENCE IN ANY PARTICULAR SOLN IS LOW AT THIS TIME. RAUSCH