EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1159 AM EDT THU JUN 22 2017 VALID 12Z SUN JUN 25 2017 - 12Z THU JUN 29 2017 ...PATTERN OVERVIEW/MODEL EVALUATION... AN AMPLIFIED WRN RIDGE/ERN TROUGH PATTERN WILL TREND FLATTER WITH TIME, AS ERN/NERN PAC TROUGH ENERGY ERODES THE WRN RIDGE WITH THIS EVOLUTION EVENTUALLY LEADING TO A WEAKER ERN U.S. MEAN TROUGH. DOMINANT UNCERTAINTIES CARRY OVER FROM PREVIOUS CYCLES. THESE INCLUDE TRACK/TIMING OF THE NERN PAC UPR LOW MOVING INTO CANADA, DETAILS OF THE TROUGH TO THE S OF THE UPR LOW, AND FARTHER EWD THE SHRTWV DETAILS WITHIN THE ERN U.S. MEAN TROUGH. FROM THE ERN PAC INTO THE CENTRAL PART OF THE CONTINENT, GFS/GEFS RUNS CONTINUE TO TRACK THE NERN PAC UPR LOW SOMEWHAT FARTHER SWD THAN MOST OTHER SOLNS THUS LEADING TO LOWER HGTS ALOFT OVER THE WEST. WHILE THE SRN TRACK HAS BEEN SOMEWHAT CONSISTENT OVER THE PAST DAY OR TWO IN THE GFS, TIMING HAS VARIED CONSIDERABLY. THIS INCLUDES THE 00Z/06Z GFS RUNS WHICH ARE SLOWER/FASTER RESPECTIVELY. TROUGHING TO THE S OF THE UPR LOW WILL INCORPORATE A LOWER LATITUDE UPR LOW FCST TO BE OFFSHORE THE WEST COAST AROUND 40N LATITUDE AS OF 12Z MON. THE COMBINATION OF THIS ENERGY WILL SUPPORT SRN CANADA/NRN TIER LOW PRESSURE AND ASSOC FRONTAL SYSTEM. THERE APPEARS TO BE A GENERAL TREND OVER RECENT ENSEMBLE MEAN RUNS TOWARD A SLIGHTLY FASTER BUT BETTER DEFINED SYSTEM. THE FASTER TREND SEEMS REASONABLE GIVEN THE EVOLUTION TOWARD FLATTER FLOW ALOFT. STILL PREFER TO TILT THE FCST BLEND TO THE N OF THE GFS FOR THE UPR LOW TRACKING INTO CANADA BUT THERE HAS BEEN ENOUGH PERSISTENCE TO GIVE ITS SOLNS PARTIAL MINORITY CONSIDERATION. TELECONNECTIONS RELATIVE TO THE ALEUTIANS NEG HGT ANOMALY CENTER AND NERN PAC POS ANOM CENTER IN D+8 CHARTS CONTINUE TO SUPPORT POTENTIAL FOR SOME DEGREE OF MEAN TROUGHING ALONG OR INLAND FROM THE WEST COAST. THIS ALSO FAVORS AN INTERMEDIATE SOLN WITH A LITTLE MORE WRN TROUGHING THAN THE ECMWF/ECMWF MEAN LATE IN THE PERIOD, THOUGH IT SHOULD BE NOTED THAT THE ECMWF MEAN DOES EVENTUALLY DEVELOP SOME TROUGHING AFTER DAY 7 THU. OVER THE EAST THE THEME CONTINUES TO BE ABOVE AVG CONFIDENCE IN THE MEAN TROUGH BUT LOW CONFIDENCE IN THE DETAILS. MODELS ARE STILL SHUFFLING AROUND FROM RUN TO RUN FOR EXACTLY HOW ONE OR MORE SFC WAVES EVOLVE NEAR THE EAST COAST INTO EXTREME ERN CANADA IN ASSOC WITH SHRTWV ENERGY ALOFT. THE GENERAL CONSENSUS FROM THE PAST COUPLE DAYS OF GUIDANCE HAS BEEN FOR SFC FEATURES TO BE FAIRLY WEAK. THERE IS BETTER AGREEMENT ON TRAILING HIGH PRESSURE BUILDING FROM THE PLAINS INTO THE EAST. AFOREMENTIONED TELECONNECTIONS YIELD A HINT OF FLAT CYCLONIC FLOW OVER THE EAST FOR LATE PERIOD AND BEYOND. AN OPERATIONAL BLEND INCORPORATING VARIOUS ASPECTS OF THE 00Z-06Z GFS AND 00Z ECMWF/UKMET/CMC REPRESENTS FCST PREFS WELL FROM DAY 3 SUN INTO DAY 5 TUE WHILE ADDING SOME 06Z GEFS/00Z ECMWF MEAN INPUT HELPS TO TONE DOWN DETAIL UNCERTAINTIES LATER IN THE PERIOD. THE RESULTING FCST IS FAIRLY CLOSE TO CONTINUITY ALOFT WHILE SFC DETAILS ADJUST A LITTLE MORE TO REFLECT THE MOST COMMON IDEAS OF LATEST GUIDANCE. ...WEATHER HIGHLIGHTS... A SLOWLY MOVING OR STALLED WAVY FRONT NEAR THE GULF COAST/NRN FLORIDA WILL PROVIDE A FOCUS FOR PERIODS OF SHWRS/TSTMS. ALSO HIGH PRESSURE TO THE N OF THE FRONT WILL PROMOTE A PERIOD OF LOW LVL UPSLOPE FLOW AND POTENTIAL CONVECTIVE ENHANCEMENT ALONG THE ERN SLOPES OF THE SRN ROCKIES/SRN HIGH PLAINS. IN BOTH CASES SOME LOCALLY HVY ACTIVITY IS PSBL. ERN PAC UPR LOW ENERGY EJECTING INLAND MAY PROVIDE A BRIEF PERIOD OF CONVECTIVE POTENTIAL OVER THE NORTHWEST MON-TUE. EXPECT GREATER COVERAGE/INTENSITY OF CONVECTION TO SPREAD ACROSS THE PLAINS/MS VALLEY FROM ABOUT TUE NIGHT ONWARD AHEAD OF ENERGY ALOFT EMERGING FROM THE WRN U.S./SWRN CANADA AND ASSOC SFC SYSTEM. SOME OF THIS CONVECTION MAY BE STRONG AND/OR HEAVY BUT IT WILL TAKE SOME TIME TO RESOLVE THE MOST FAVORED FOCUS WITH A REASONABLE DEGREE OF CONFIDENCE. LOCATIONS FROM THE UPR MS VALLEY THROUGH GREAT LAKES/NORTHEAST MAY SEE SOME DIURNALLY FAVORED PRECIP UNDER THE CORE OF THE UPR TROUGH SUN ONWARD, WITH A GRADUAL DIMINISHING OF ACTIVITY FROM WEST TO EAST CORRESPONDING TO TROUGH PROGRESSION. CONTINUE TO EXPECT A MODERATION OF TEMPS ACROSS MUCH OF THE LOWER 48 AS THE PATTERN ALOFT TRENDS LESS AMPLIFIED BY DAYS 6-7 WED-THU, AT WHICH TIME MOST MIN/MAX ANOMALIES SHOULD SETTLE INTO THE SINGLE DIGITS. EARLIER IN THE PERIOD THE NWRN STATES MAY SEE SOME HIGHS 10-20F OR MORE ABOVE NORMAL WHILE AREAS TO THE S MAY BE 10-15F ABOVE NORMAL. A FEW DAILY RECORD HIGHS/WARM MINS ARE PSBL. MEANWHILE AN AREA FROM THE CNTRL HIGH PLAINS INTO UPR MS VLY MAY SEE HIGHS 10-20F BELOW NORMAL ON SUN WITH MUCH OF THE REST OF THE CNTRL-ERN U.S. FAIRLY COOL AS WELL. AN ISOLD RECORD LOW/COOL MAX MAY BE PSBL ESPECIALLY WHERE THERE IS A SHORTER PERIOD OF RECORD. RAUSCH