EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1152 AM EDT SUN SEP 28 2014 VALID 12Z WED OCT 01 2014 - 12Z SUN OCT 05 2014 ...OVERVIEW... MODEL/ENSEMBLE SOLNS DISPLAY AT LEAST AVG CLUSTERING/CONTINUITY IN THE LARGE SCALE... WITH AN AMPLIFIED/DEEP AND SLIGHTLY NEGATIVELY TILTED TROUGH PROGRESSING FROM THE W-CENTRAL STATES TO A POSN COVERING THE ERN HALF OF THE CONUS BY LATE IN THE WEEKEND. THIS TROUGH WILL PUSH A WAVY COLD FRONT FROM THE PLAINS TO EAST COAST. AT THE SAME TIME FAIRLY STRONG UPSTREAM RIDGING ALOFT WILL BUILD OVER THE WEST. THIS AMPLIFIED PATTERN COULD BE ENHANCED DEPENDING ON HOW WRN PAC T.S. KAMMURI INTERACTS WITH SURROUNDING/DOWNSTREAM FLOW. MEANWHILE GUIDANCE FINALLY APPEARS TO BE STARTING A TREND TOWARD A COMMON SCENARIO FOR THE RECENTLY PROBLEMATIC LEAD TROUGH/UPR LOW NEAR THE EAST COAST AND TO A LESSER EXTENT AN ASSOC WRN ATLC SFC LOW EVOLUTION. ...GUIDANCE EVALUATION/PREFERENCES... WITHIN THE W-CNTRL TO ERN CONUS MEAN TROUGH... WRN CONUS TO PLAINS SHRTWV ENERGY DAYS 3-4 WED-THU IS FCST TO DEVELOP A S-CNTRL PLAINS WAVE THAT LIFTS NEWD. MOST OPERATIONAL SOLNS THEN SUGGEST THAT AMPLIFYING WRN CANADA ENERGY IMMEDIATELY UPSTREAM MAY DEEPEN THIS WAVE SIGNIFICANTLY BY THE TIME IT REACHES WRN-UPR GRT LKS BY DAY 5 FRI. ASIDE FROM PROBLEMATIC RUN TO RUN DIFFS...THE GFS/ECMWF HAVE BEEN SHOWING THIS IDEA FOR THE PAST COUPLE DAYS AND BLENDING OF THE ENSEMBLES RESULTED IN A LESS DEEP LOW AMID UNCERTAINTY. GRADUAL DEEPENING OF THE TROUGH ALOFT IN THE ENSEMBLE MEANS LEADS TO A CONSENSUS THAT IS ALSO A TAD FASTER WITH THE FRONT TRAILING FROM THIS SFC LOW DURING THE LATTER HALF OF THE PERIOD. DEPENDING ON EXACTLY HOW SHRTWV ENERGY EVOLVES THERE COULD ALSO BE A WEAK FRONTAL WAVE NEAR THE EAST COAST BY NEXT SUN. OUR PREFERENCE FOR THE ENSEMBLE MEANS SUGGESTS MINIMAL SUPPORT OF THE 00 UTC ECMWF THAT HAS BROKEN RUN TO RUN CONTINUITY WITH A MORE PROGRESSIVE/LESS AMPLIFIED MID-UPPER LEVEL TROUGHING AND PATTERN BY THEN. BY DAY 7 SUN UPSTREAM NRN PAC ENERGY FLOWING AROUND THE WRN RIDGE IS FCST TO SUPPORT A S-CENTRAL CANADAIAN SFC WAVE AND WARM FRONT EXTENDING INTO THE N-CENTRAL US. AS IS USUALLY THE CASE BY THAT TIME FRAME THERE ARE SOME MEANINGFUL DETAIL DIFFS BUT THE AFOREMENTIONED BLEND PROVIDES A GOOD INTERMEDIATE SOLN. ALONG THE EAST COAST...INTO EARLY DAY 4 THU GUIDANCE IS SHOWING MODEST AGREEMENT FOR THE TROUGH/UPR LOW FCST TO DRIFT THROUGH THE LONGWAVE MEAN RIDGE. SOLNS DIVERGE MORE OVER TIME. THIS REMAINS A DIFFICULT FCST GIVEN TYPICAL DIFFICULTIES OF RESOLVING WEAK ENERGY WITHIN A MEAN RIDGE. IN PARTICULAR WILL HAVE TO WATCH THE STRENGTH OF RIDGING SFC/ALOFT OVER THE CANADIAN MARITIMES... IF SUFFICIENT IT COULD LEAD TO A LINGERING SYSTEM AND EVEN A BRIEF PERIOD OF RETROGRESSION FOR THE SYSTEM OF INTEREST. ...SENSIBLE WEATHER HIGHLIGHTS... ALONG THE SFC FRONT CROSSING THE ERN HALF OF THE CONUS... EXPECT THE BEST POTENTIAL FOR HEAVIEST RNFL FROM THE ERN PLAINS/MS VLY INTO THE WRN-UPR GRTLKS IN ASSOC WITH STRONGEST DYNAMICS ALOFT/SFC WAVE DEVELOPMENT ALONG WITH SOME INPUT OF MSTR FROM GULF INFLOW. SPC IS ALSO OUTLOOKING AN ASSOCIATED THREAT FOR SEVERE WEATHER INVOF OK/KS/MO WED INTO THU. A BRIEF PERIOD OF ATLC INFLOW COULD THEN ALSO ENHANCE AMTS OVER THE NORTHEAST LATE IN THE PERIOD BUT TO WHAT EXTENT WILL DEPEND ON SPEED OF THE FRONT. MEANWHILE THE FRONT EXTENDING FROM THE WRN ATLC SYSTEM MAY FOCUS RNFL OVER FLORIDA AND ELY LOW LVL FLOW MAY SUPPORT RNFL OVER SRN TX FOR A TIME. BY THE END OF THE FCST PERIOD THE LARGE SCALE PATTERN... PERHAPS MORE REMINISCENT OF WINTER... SHOULD YIELD AN UNUSUALLY LARGE AREA OF DRY WEATHER ACROSS THE LOWER 48. COLDEST ANOMALIES FOR DAYTIME TEMPS SHOULD FOLLOW THE CORE OF THE UPR TROUGH AND BE MOST PRONOUNCED DAYS 3-5 WED-FRI WITH READINGS 10-15F BELOW NORMAL FROM PARTS OF THE GRTBASIN/ROCKIES INTO THE NRN PLAINS. EXPECT A BROAD AREA OF MIN TEMPS 10-20F ABOVE NORMAL IN THE WARM SECTOR AHEAD OF THE COLD FRONT WITH LESS EXTREME ANOMALIES FOR HIGHS. AFTER A COOL START TO THE PERIOD... WRN LOCATIONS WILL SEE A TREND TO ABOVE NORMAL TEMPS AS RIDGING ALOFT BUILDS INTO THE REGION. SCHICHTEL