EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 311 AM EDT FRI OCT 14 2016 VALID 12Z MON OCT 17 2016 - 12Z FRI OCT 21 2016 ...WRN US HEAVY PCPN ENDS EARLY NEXT WEEK WITH NEW FOCUS INTO THE SERN US LATER NEXT WEEK... ...GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER HIGHLIGHTS/THREATS... THE NEXT IN A SERIES OF POTENT TROUGH/JET ENERGIES SLAM INTO AND ACROSS THE COOLING WRN US MID-LATITUDES AGAIN MON IN A CONTINUING VERY WET AND UNSETTLED FLOW PATTERN THREAT. STRONG DYNAMICS AND A LINGERING MOISTURE CONNECTION WILL PRODUCE A BURST OF HEAVIER PCPN INCLUDING ELEVATION SNOWS. MAX ENERGY PROGRESSES TO THE N-CENTRAL US TUE TO SUPPORT CYCLOGENESIS/FRONTOGENESIS...BUT MOISTURE MAY PROVE RELUCTANT TO RETURN IN ERNEST. SUSPECT HEAVIEST PCPN WILL OCCUR OVER SRN CANADA AROUND THE MAIN LOW. THE TRAILING FRONT WILL FOCUS WIDESPREAD BUT MODEST PCPN FOR THE MOST PART BUT PROVIDE POST-FRONTAL COOLING ACROSS THE CENTRAL THEN ERN US AS THE DEEPENED MAIN LOW LIFTS INTO ERN CANADA. PREFER A COMPOSITE PROGRESSION CLOSER TO THE 12/18 UTC GFS AND 12 UTC ECMWF IN FLATTENED FLOW VS THE SLOWER 12 UTC UKMET. THIS SEEMS WELL SUPPORTED BY ENSEMBLES AND NOW THE MORE RECENT 00 UTC UKMET HAS TRENDED FASTER TO FURTHER BOLSTER FORECAST CONFIDENCE. ADDITIONAL PACIFIC TROUGH/JET ENERGIES PROGRESS INTO THE WEST ON THE HEELS OF THE LEAD SYSTEM TUE WITH A LESSER EFFECT. THIS MAY END THE WET PATTERN. THERE SEEMS TO BE ABOVE NORMAL PREDICTABILITY ASSOCIATED WITH SUBSEQUENT POST SYSTEM RIDGE BUILDING OVER THE WRN NOAM DOWNSTREAM OF MORE AMPLE MID-LATER WEEK ERN/NERN PACIFIC TROUGH AMPLIICATION THAT IS COMMON TO MOST GUIDANCE. RECENT MODELS AND ENSEMBLES HAVE ACCORDINGLY SHOWN A STRONG TREND TO ALLOW THIS FLOW TRANSITION TO MEANWHILE SUPPORT AN INCREASING THREAT FOR MID-UPPER LEVEL TROUGH AMPLIFICATION AND SEPARATION LATER WEEK ACROSS THE E-CENTRAL/SRN US. THIS COULD PROVIDE A CONNECTION WITH UNDERCUT CLOSED LOW ENERGY THAT SLOWLY TUCKS BACK OVER FL THEN THE GULF OF MEX NEXT WEEK AND ALLOW DEEP LOW LATITUDE MOISTURE WORK UP INTO THE SRN/SERN US ALONG/AHEAD OF THE WAVY TRAILING FRONT TO FUEL HEAVY RAIN. THE 12 UTC ECMWF OFFERS A DEEPER SURFACE LOW APPROACH THREAT THAN MOST GUIDANCE...BUT THE 18 UTC GFS HAS TRENDED TO SHOW MORE LOWER LEVEL CYCLONNIC FLOW EMINATING FROM THE GULF. THE 12/00 UTC CANADIAN RUNS STILL ALSO OFFERS A LESS LIKELY TROPICAL LOW THREAT UP THE SE/ERN COAST THAT HAS MINIMAL ENSEMBLE SUPPORT. THE CANADIAN HAS A HISTORICALLY HIGH BIAS WITH THESE TYPES OF SYSTEMS...BUT ANY THREAT WILL BE MONITORED GIVEN POTENTIAL LOWER LATITUDE CONNECTION WITH FLOW AMPLIFICATION. OVERALL...THE WPC MEDIUM RANGE PRODUCT SUITE HAS BEEN PRIMARILY DERIVED FROM A COMPOSITE BLEND OF REASONABLY WELL CLUSTERED GUIDANCE FROM THE 18 UTC GEFS MEAN...12 UTC NAEFS/ECMWF ENSEMBLE MEANS...AND PERHAPS THE 18 UTC GFS TO ADD A BIT MORE DETAIL FROM A MODEL THAT SEEMS TO FOLLOW THE ABOVE THEMES/TRENDS/CONTINUITY CONSISTENT WITH LINGERING UNCERTAINTY. SCHICHTEL