EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 240 AM EDT SUN SEP 28 2014 VALID 12Z WED OCT 01 2014 - 12Z SUN OCT 05 2014 ...OVERVIEW... LATEST MODEL/ENSEMBLE SOLNS DISPLAY BETTER THAN 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 FLOW. MEANWHILE GUIDANCE FINALLY APPEARS TO BE STARTING A TREND TOWARD A COMMON SCENARIO FOR THE RECENTLY PROBLEMATIC TROUGH/UPR LOW NEAR THE EAST COAST AND ASSOC WRN ATLC SFC 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 SHOULD DEEPEN THIS WAVE SIGNIFICANTLY BY THE TIME IT REACHES WRN-UPR GRTLKS BY DAY 5 FRI. ASIDE FROM TYPICAL RUN TO RUN DIFFS THE GFS/ECMWF HAVE BEEN SHOWING THIS IDEA FOR THE PAST COUPLE DAYS. GRADUAL DEEPENING OF THE TROUGH ALOFT IN THE ENSEMBLE MEANS LEADS TO A CONSENSUS THAT IS 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. THROUGH THE 18Z CYCLE GOOD CLUSTERING IN PRINCIPLE FAVORED A COMPROMISE AMONG THE 12Z-18Z GFS/12Z ECMWF AND 18Z GEFS/12Z ECMWF ENSEMBLE MEANS. THUS FAR NEW 00Z GUIDANCE MAINTAINS SUPPORT FOR THIS APPROACH. BY DAY 7 SUN UPSTREAM NRN PAC ENERGY FLOWING AROUND THE WRN RIDGE IS FCST TO SUPPORT A SRN CANADA SFC WAVE AND WARM FRONT EXTENDING INTO THE NRN TIER CONUS. AS IS USUALLY THE CASE BY THAT TIME FRAME THERE ARE SOME MEANINGFUL DETAIL DIFFS BUT THE AFOREMENTIONED BLEND PROVIDES A GOOD INTERMEDIATE SOLN. THE NEW 00Z GFS IS SLIGHTLY FASTER THAN MOST OTHER SOLNS. ALONG THE EAST COAST... AT LEAST INTO EARLY DAY 4 THU THE NEW 00Z GUIDANCE IS SHOWING THE BEST AGREEMENT YET FOR THE TROUGH/UPR LOW FCST TO DRIFT THROUGH THE LONGWAVE MEAN RIDGE. SOLNS DIVERGE SOMEWHAT THEREAFTER. 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 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. A BRIEF PERIOD OF ATLC INFLOW COULD 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. RAUSCH