EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1157 AM EDT SAT JUN 03 2017 VALID 12Z TUE JUN 06 2017 - 12Z SAT JUN 10 2017 MORNING UPDATE... MODEL GUIDANCE REMAINED IN VERY GOOD AGREEMENT WITH THE LONG WAVE PATTERN SETTING UP OVER THE LOWER 48 NEXT WEEK...WHICH WILL BE DOMINATED BY AN AMPLIFYING UPPER TROUGH IN THE NORTHWEST...MEAN RIDGING OVER THE CENTRAL/NORTHERN ROCKIES AND PLAINS...AND PERSISTENT TROUGHING FROM THE GREAT LAKES TO THE NORTHEAST AND MID-ATLANTIC STATES. THE UPDATED DAY 3-7 FORECAST WAS BASED ON A BLEND OF THE VERY SIMILAR GFS/ECMWF/GEFS MEAN/ECMWF ENSEMBLE MEAN (WITH THE DETERMINISTIC GFS/ECMWF USED HEAVILY THROUGH THE FORECAST PERIOD DUE TO THEIR UNUSUALLY GOOD AGREEMENT WITH A LARGE UPPER LOW MOVING IN OVER THE NORTHWEST LATE NEXT WEEK)...WHICH RESULTED IN NO MAJOR CHANGES FROM CONTINUITY. HOWEVER...THERE CONTINUES TO BE SOME UNCERTAINTY WITH THE PROGRESSION OF A CLOSED LOW EXITING THE GREAT LAKES REGION ON TUESDAY. THE 06Z GFS STAYED IN SUPPORT OF THE ECMWF (WHICH HAS BEEN CONSISTENTLY ON THE FASTER SIDE OF MODEL SPREAD WITH THIS FEATURE)...BUT THE 00Z CMC/UKMET AND SEVERAL INDIVIDUAL ENSEMBLE MEMBERS SUGGEST THERE IS STILL THE POTENTIAL FOR A SLOWER EXITING OF THE CLOSED LOW THAN WHAT IS CURRENTLY IN THE FORECAST. ...PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT... MODELS/ENSEMBLES MAINTAIN REASONABLE AGREEMENT ON A FAIRLY AMPLIFIED MEAN PATTERN CONSISTING OF A ROCKIES/PLAINS RIDGE BTWN AN ERN U.S. TROUGH AND DEEPER ERN PAC TROUGH APPROACHING THE WEST COAST. HOWEVER THERE ARE PERSISTENT AND SIGNIFICANT QUESTION MARKS ABOUT EMBEDDED DETAILS, ESPECIALLY OVER THE EAST. FOR THE UPR LOW FCST TO REACH THE ERN GRTLKS BY EARLY DAY 3 TUE AND OVERALL ERN TROUGH, GUIDANCE BEGINS TO DIVERGE FROM THE START OF THE PERIOD. SIMILAR 18Z AND NEW 00Z GFS RUNS HAVE TRENDED FASTER FROM SOME PRIOR RUNS LEADING TO MORE PROGRESSIVE EJECTION OF THE UPR LOW IN A FASHION SIMILAR TO RECENT ECMWF RUNS AND THE 12Z ECMWF MEAN THAT WAS SLIGHTLY FASTER THAN EARLIER RUNS. ON THE OTHER HAND GEFS MEANS STILL HOLD BACK SOMEWHAT MORE TROUGH ENERGY, REFLECTING A COMBINATION OF POTENTIALLY SLOWER CLOSED LOW EJECTION IN SOME MEMBERS AND LINGERING ENERGY THAT REMAINS EVEN IN THE LATEST GFS RUNS/12Z ECMWF. NEW UKMET/CMC RUNS CONTINUE TO BRING THE CLOSED LOW FARTHER W/SW THAN OTHER SOLNS. THIS FCST APPEARS VERY SENSITIVE TO TWO INDIVIDUAL PIECES OF UPSTREAM ENERGY TRACKING ACROSS SRN AND CNTRL CANADA. THE UKMET/CMC ARE BOTH ON THE SLOW SIDE OF THE SPREAD WITH THE SRN FEATURE AND FAST WITH THE NRN ONE. TOWARD MID-LATE PERIOD IT SEEMS REASONABLE THAT INITIAL ERN TROUGHING SHOULD EJECT FASTER THAN THE UKMET/CMC TO SOME DEGREE GIVEN THE EVOLUTION OF CANADIAN FLOW BEGINNING TO RELOAD THE MEAN TROUGH IN RESPONSE TO THE WRN CANADA RIDGE. STILL THE DETAILS OF THIS RELOADING FLOW ARE UNCERTAIN AS WELL, IN PARTICULAR THE 12Z ECMWF IDEA OF PULLING THE CNTRL CANADA UPR LOW INTO SERN CANADA. ON THE SRN AND ERN SIDE OF THE ERN TROUGH GUIDANCE SHOWS A COLD FRONT PUSHING FROM THE SRN STATES INTO THE GULF OF MEXICO/FL PENINSULA/WRN ATLC, INTERACTING WITH A BROAD STREAM OF MOIST SWLY/W-SWLY FLOW FLOW ALOFT. SOME INDIVIDUAL SOLNS HAVE BEEN DEPICTING ONE OR MORE SFC WAVES OF VARYING CHARACTER ALONG/AHEAD OF THE FRONT. LATEST GUIDANCE IS SUGGESTING THAT ANY WAVES THAT FORM WILL MORE LIKELY BE IN RESPONSE TO DYNAMICS ALOFT AND ALONG THE FRONTAL BNDRY. CONFIDENCE IS STILL LOW ON SPECIFICS OF ENERGY PROGRESSING EWD FROM THE WRN GULF COAST AND PSBL INTERACTING NRN STREAM FLOW ALONG WITH THE ASSOC SFC WAVES, BUT THE ECMWF/GFS REPRESENT THE SFC WAVE POTENTIAL IN PRINCIPLE. THE MOST PROMINENT TRENDS OVER THE PAST 24-36 HRS FOR THE TROUGH NEARING THE WEST COAST HAVE BEEN TOWARD A MORE AMPLIFIED FEATURE WITH A FARTHER SWD EMBEDDED CLOSED LOW. OPERATIONAL GFS/ECMWF RUNS ARE FARTHEST S WITH THE UPR LOW TRACK BY DAYS 6-7 FRI-SAT WITH THE GEFS MEAN SHOWING MORE OF A TREND IN THIS DIRECTION THAN THE 12Z ECMWF MEAN AND ESPECIALLY THE 12Z CMC MEAN. IN THE OPERATIONAL RUNS GREATEST STANDARDIZED ANOMALIES WITHIN THE TROUGH JUST S OF THE UPR LOW REACH THE MINUS 2-3 RANGE. GIVEN THE RELATIVE NEWNESS OF THE TREND A SOLN BTWN THE MODELS AND ENSEMBLE MEANS LOOKS MOST REASONABLE AT THIS TIME, WITH ENOUGH OF A TREND EXISTING TO TRACK THE UPR LOW S OF THE CMC/ECMWF MEANS LATE IN THE PERIOD. THE UPDATED FCST STARTED WITH A BLEND OF VARYING WEIGHTS OF THE 18Z GFS/GEFS MEAN AND 12Z ECMWF/ECMWF MEAN, WITH A LITTLE 12Z GFS INCLUDED AS WELL DAYS 3-5 TUE-THU FOR ITS SLOWER ERN U.S. UPR LOW. OPERATIONAL MODEL WEIGHT WAS SUFFICIENTLY LOW TO DOWNPLAY THE LOWEST CONFIDENCE ASPECTS OF EACH RUN. THE RESULTING FCST YIELDED THE DESIRED CONTINUITY FOR UPR LVL FLOW OVER THE EAST WITH THE ONLY SFC ADJUSTMENT BEING A MORE SUPPRESSED GULF/FL PENINSULA/WRN ATLC FRONT LATE IN THE PERIOD. MEANWHILE THE BLEND HAS THE ERN PAC UPR LOW TRACKING TOWARD VANCOUVER ISLAND BY SAT. ...WEATHER HIGHLIGHTS... THE SRN TIER COLD FRONT PUSHING INTO THE GULF OF MEXICO/FL PENINSULA AND THEN LIKELY STALLING, IN COMBINATION WITH IMPULSES ALOFT AND BROAD MOIST FLOW ALONG/S OF THE FRONT, WILL PROVIDE A FOCUS FOR AREAS OF HEAVY RAIN DURING THE PERIOD. THE FL PENINSULA SHOULD HAVE THE GREATEST POTENTIAL FOR SIGNIFICANT TOTALS OVER THE 5-DAY PERIOD. SOME ENHANCED RNFL IS ALSO PSBL OVER THE NERN STATES WITH THE UPR LOW AFFECTING THE REGION FOR A PORTION OF NEXT WEEK. THE CNTRL-SRN ROCKIES WILL SEE EPISODES OF SHWRS/TSTMS WITH SOME ACTIVITY EXTENDING NEWD ALONG A FRONT PUSHING INTO THE NRN TIER. MEANWHILE THE STRONG UPR TROUGH NEARING THE WEST COAST WILL BRING A DECENT AMOUNT OF MSTR/RAIN FOR THE TIME OF YEAR INTO THE NRN HALF OF THE WEST COAST AND EXTENDING INTO THE EXTREME NRN ROCKIES. WEST COAST STATES WILL SEE A COOLING TREND LATE WEEK WITH THE ARRIVAL OF THE UPR TROUGH. IN ADVANCE OF THE COOLER AIR, EXPECT WELL ABOVE NORMAL TEMPS WITH DECENT COVERAGE OF AT LEAST PLUS 10-20F ANOMALIES ACROSS THE WEST AND EVENTUALLY EXTENDING INTO THE NRN PLAINS. LOCATIONS FROM THE ERN GRTLKS/CNTRL APLCHNS INTO NEW ENGLAND SHOULD SEE COLD ANOMALIES OF SIMILAR MAGNITUDE EARLY IN THE PERIOD. MORE BROADLY, GENERALLY COOL READINGS OVER MUCH OF THE EAST THROUGH MIDWEEK SHOULD STEADILY MODERATE TOWARD NORMAL. RAUSCH