EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 305 AM EDT SAT OCT 15 2016 VALID 12Z TUE OCT 18 2016 - 12Z SAT OCT 22 2016 ...GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER HIGHLIGHTS/THREATS... MAJOR TROUGH ENERGIES IN WHAT HAS BEEN A TURBULENT EPISODE OVER THE WRN US PROGRESS TO THE N-CENTRAL US MON TO SUPPORT CYCLOGENESIS/FRONTOGENESIS. 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. DEEP MOISTURE MAY PROVE RELUCTANT TO RETURN IN ERNEST IN ANTICIPATION OF UPSTREAM TROUGH AMPLIFICATION AND FRONTAL WAVE DEVELOPMENT BACK OVER VICINITY OF THE S-CENTRAL PLAINS TUE. THEREAFTER...THERE STILL SEEMS TO BE ABOVE NORMAL PREDICTABILITY WITH CONCURRENT RIDGE BUILDING OVER THE WRN NOAM DOWNSTREAM OF MORE AMPLE MID-LATER WEEK ERN/NERN PACIFIC TROUGH AMPLIICATION THAT IS COMMON TO MOST GUIDANCE. HOWEVER....THE ULTIMATE SHAPE OF THIS RIDGE HAS BECOME HIGHLY UNCERTAIN WITH RESPECT TO SUBSEQUENT DOWNSTREAM TROUGH AMPLIIFATION....BUT WHERE? THE GFS IS BACK OVER THE ROCKIES/PLAINS AND THE ECMWF IS MORE PROGRESSIVE OVER THE E-CENTRAL THEN ERN/SERN US. THE ENSEMBLE MEANS OVER A MUCH MORE COMPATABLE AND COMPROMISE SOLUTION IN BETWEEN. WITH THIS IDEA AND AMPLITUDE POTENTIAL A CONNECTION COULD STILL DEVELOP WITH UNDERCUTTING LOW ENERGY THAT SLOWLY TUCKS BACK OVER FL THEN THE GULF OF MEX AND ALLOW DEEPER LOW LATITUDE MOISTURE WORK UP INLAND FROM THE SRN/SERN US ALONG/AHEAD OF THE WAVY TRAILING FRONT TO FUEL HEAVY RAIN. OVERALL...THE WPC MEDIUM RANGE PRODUCT SUITE HAS BEEN PRIMARILY DERIVED FROM A COMPOSITE BLEND OF THE 12 UTC GEFS MEAN/NAEFS/ECMWF ENSEMBLE MEANS IN A PATTERN WITH RAPIDLY INCREASING FORECAST SPREAD OVER TIME. FORECAST PREDICTABILITY IS BELOW AVERAGE GIVEN THAT DESPITE ENSEMBLE MEAN COMPATABILLITY...DETERMINISTIC MODEL AND INDIVIDUAL ENSEMBLE MEMBER GUIDANCE HAS BECOME HIGHLY VARIED OVER THE PAST FEW RUNS AND OFFERS CHANGING DAILY TRENDS WITHOUT A STRONG COMPELLING METEOROLOGICAL REASON TO EMBRACE A PARTICULAR SOLUTION YET. SCHICHTEL