EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 241 AM EDT SUN JUN 19 2016 VALID 12Z WED JUN 22 2016 - 12Z SUN JUN 26 2016 ...PATTERN OVERVIEW... AROUND A PERSISTENT SRN ROCKIES/PLAINS RIDGE... EXPECT THE MEAN TROUGH JUST OFF THE WEST COAST TO TREND WEAKER BY NEXT WEEKEND WHILE ANOTHER MEAN TROUGH REMAINS NEAR THE EAST COAST. WITHIN THIS GENERAL SCENARIO THERE IS STILL A FAIR AMOUNT OF UNCERTAINTY REGARDING SPECIFICS OF ENERGY EJECTING FROM THE ERN PAC TROUGH ALONG WITH ASSOC SFC EVOLUTION AND CONVECTION. ...GUIDANCE/UNCERTAINTY ASSESSMENT... ALBEIT WITH CONSIDERABLE SPREAD STILL EXISTING... FOR ABOUT THE PAST DAY THE OPERATIONAL MODELS HAVE STARTED TO KEY ON A LEADING SHRTWV EJECTING THROUGH THE PAC NW IN THE SHORT RANGE AND REACHING SRN CANADA/NRN HIGH PLAINS BY AROUND 12Z DAY 3 WED. THIS SHRTWV THEN SUPPORTS A SFC WAVE THAT CROSSES THE ERN HALF OF THE COUNTRY WED-THU AND REACHES THE WRN ATLC BY FRI. WITH THE ARRIVAL OF THE 12Z/18Z CYCLE OF GUIDANCE THE MODELS HAD PROVIDED ENOUGH OF A SIGNAL TO ADJUST CONTINUITY IN THAT DIRECTION BUT NOT TO THE EXTENT OF THE 18Z GFS/12Z UKMET THAT WERE STRONGEST AND FARTHEST NWD WITH THE SFC WAVE. THE 18Z GEFS MEAN WAS ALSO SUPPORTIVE OF A MORE MODERATE WAVE WHILE THE 12Z ECMWF/CMC MEANS REMAINED ILL-DEFINED. IN TERMS OF THE LARGE SCALE EVOLUTION THIS CHANGE IN CONTINUITY KEEPS THE EAST COAST MEAN TROUGH LESS AMPLIFIED FOR A WHILE... WAITING UNTIL PASSAGE OF THE EARLY-MID PERIOD SYSTEM BEFORE THE UPR TROUGH GAINS AS MUCH AMPLITUDE AS PREVIOUSLY FCST. AMONG NEW 00Z GUIDANCE THE GFS IS STILL RATHER STRONG/NWD WITH THE SFC WAVE. THE UKMET HAS ADJUSTED AWAY FROM ITS 12Z RUN BUT THE CMC IS QUITE WEAK. WITHIN THE ERN PAC TROUGH THE PRIMARY FEATURE OF INTEREST REMAINS THE UPR LOW FCST TO TRACK OVER/NEAR VANCOUVER ISLAND AND THEN CONTINUE INLAND. PERSISTENTLY HIGH SPREAD FOR TIMING AND SHIFTING TRENDS HAVE FAVORED MAINTAINING AN INTERMEDIATE SOLN. OVER THE PAST DAY THE CONSISTENTLY SLOWER GFS/GEFS MEAN CLUSTER HAS SHOWN SOME ACCELERATION IN A PARTIAL TREND TOWARD THE ECMWF/ECMWF MEAN... A DAY AFTER THE ECMWF MEAN HAD TRENDED SOMEWHAT SLOWER IN A NOD TO THE GFS/GEFS. ADDING TO THE TREND-SHIFTING THE 12Z CMC MEAN WAS SLOWER FROM A DAY EARLIER. TOWARD THE END OF THE PERIOD AND BEYOND THERE IS REASONABLE AGREEMENT ON THE ESTABLISHMENT OF MEAN TROUGHING TO THE S OF ALASKA WHICH WOULD FAVOR FLATTER FLOW OVER THE PAC NW. THIS WOULD RECOMMEND A SOLN AT LEAST SOMEWHAT FASTER THAN THE SLOW END OF THE ENVELOPE. AN ADDED WILD CARD IN THE FCST NEAR THE WEST COAST IS A SEPARATE WEAKER UPR LOW TO THE SW OF THE AFOREMENTIONED FEATURE. SOLNS HAVE RANGED FROM IT GETTING CAPTURED BY THE NRN STREAM SYSTEM... AS IN THE 18Z GFS... TO LINGERING FOR A WHILE BEFORE COMING ASHORE AS IN THE 00Z GFS/CMC AND PAST COUPLE RUNS OF THE ECMWF. CONFIDENCE IS MINIMAL FOR THIS FEATURE GIVEN THE DIFFICULTY GUIDANCE HAS HAD WITH LEADING FEATURES. THE UPDATED FCST USED VARIOUS COMPONENTS OF THE 12Z-18Z GFS/12Z ECMWF AND 18Z GEFS/12Z ECMWF MEANS TO CAPTURE A MODERATE DEPICTION OF CONTINUITY CHANGES OVER THE ERN HALF OF THE LOWER 48 WED INTO FRI WHILE MAINTAINING AN INTERMEDIATE SOLN FOR ENERGY WITHIN THE ERN PAC TROUGH. AFTER DAY 4 THU THE 12Z ECMWF TRENDED OUT OF PHASE RELATIVE TO ENOUGH OTHER GUIDANCE TO FAVOR ITS EXCLUSION AND CONFIDENCE IN GFS SPECIFICS DECLINED TO 10-20 PCT MID-LATE PERIOD SO BY THEN THE ENSEMBLE MEANS DOMINATED THE FCST. ...WEATHER HIGHLIGHTS/THREATS... EXPECT HOT WEATHER TO CONTINUE OVER A MAJORITY OF THE WEST/PLAINS WITH SOME LOCATIONS SEEING HIGHS AT LEAST 10F ABOVE NORMAL FOR ONE OR MORE DAYS. ANOMALIES FOR MORNING LOWS MAY BE A LITTLE MORE EXTREME AT SOME LOCATIONS SO RECORD WARM LOWS MAY BE MORE NUMEROUS THAN RECORD HIGHS. ACROSS NRN PARTS OF THE WEST PASSAGE OF ONE OR MORE SHRTWVS/SFC FRONTS MAY KEEP TEMPS MORE MODERATE AND BRING ONE OR MORE EPISODES OF CONVECTION THAT MAY EXTEND INTO THE NRN PLAINS. FARTHER EWD IMPORTANT DETAILS ARE YET TO BE RESOLVED BUT THERE IS GRADUALLY INCREASING SIGNAL TOWARD THE EXISTENCE OF A PLAINS TO WRN ATLC SYSTEM WED ONWARD WHICH WILL BE ACCOMPANIED BY ORGANIZED CONVECTION/RNFL. SOME OF THIS ACTIVITY MAY BE LOCALLY HVY AND/OR STRONG. INTRODUCTION OF THIS SYSTEM LEADS TO A LONGER DURATION OF ABOVE NORMAL TEMPS OVER THE SOUTHEAST. ASSOC FRONT SHOULD SETTLE NEAR THE EXTREME SOUTHEAST BY LATE IN THE PERIOD AND COULD HELP TO FOCUS DIURNALLY ENHANCED CONVECTION. RAUSCH