EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 226 AM EDT WED JUN 21 2017 VALID 12Z SAT JUN 24 2017 - 12Z WED JUN 28 2017 ...PATTERN OVERVIEW/MODEL EVALUATION... THE PRIMARY CONCERNS ARE HEAVY RAIN POTENTIAL ON SAT 24 JUNE WITH THE REMNANTS OF CINDY IN TN/SRN APPALACHIANS AND THEN A GRADUAL ABATEMENT OF THE SOUTHWESTERN US HEATWAVE EARLY NEXT WEEK. THE MODELS/ENSEMBLE MEANS SHOW AN AMPLIFYING EASTERN US TROUGH DAYS 3-5 WITH THE TREND TOWARDS A DEAMPLIFICATION ON DAY 7 WED 28 JUN. THE TROUGH DEAMPLIFICATION OCCURS AS HEIGHT RISES OVER THE NORTHERN PLAINS IN RESPONSE TO AN EASTERN PACIFIC TROUGH MOVING TOWARDS THE PACIFIC NORTHWEST. WITHIN THE TROUGH ACROSS THE UPPER MS VALLEY/GREAT LAKES/NORTHEAST...THERE ARE DIFFERENCES FROM MODEL TO MODEL AND RUN TO RUN WITH THE HANDLING OF SECONDARY WAVES MOVING INTO THE BASE OF THE TROUGH AND EJECTING NORTHEAST OUT OF THE TROUGH. WITH LOW PREDICTABILITY IN SHRTWV SPECIFICS...MANUAL PROGS FAVORED THE ENSEMBLE MEANS NEXT WEEK. THE 18Z GFS/GEFS MEAN AND CANADIAN ENSEMBLE MEAN WERE FASTER TO LOWER HEIGHTS IN THE PACIFIC NORTHWEST IN RESPONSE TO THE SOUTH DRIFT OF A CLOSED LOW OVER WESTERN CANADA THAT HAD DRIFTED ONSHORE THE THE NORTHEAST PACIFIC. THE 12Z ECMWF/ECMWF ENSEMBLE MEAN WERE SLOWER IN MOVING THE LOW SOUTH. THE UPSTREAM OMEGA BLOCKING PATTERN LED TO THE LIKELIHOOD OF SLOW FORWARD MOTION...SO THE 18Z FASTER GFS SOLUTION WAS NOT USED ON DAYS 6-7...SO TEMPERATURES WOULD NOT COOL AS FAST AS THE GFS IN THE PACIFIC NORTHWEST AS A RESULT. THE MODELS AGREE ON THE ANTICYCLONE CENTERED OVER AZ/NM TO BE IN PLACE DAY 3 AND THEN SINK SOUTH INTO NORTHWEST NM WITH GRADUAL HEIGHT FALLS OCCURRING AS AN EASTERN PACIFIC TROUGH APPROACHES CA. MINOR TIMING/PHASING DIFFERENCES IN BOTH FEATURES LED TO A CONSENSUS-BASED APPROACH. THE APPROACH OF THE EASTERN PACIFIC TROUGH FORCES THE HIGHER HEIGHTS TO MOVE FURTHER INLAND WITH THE RIDGE AXIS PROGRESSING EAST ACROSS THE GREAT BASIN AND THEN ROCKIES EARLY NEXT WEEK AND FINALLY THE PLAINS BY THE MIDDLE OF NEXT WEEK. THE FCST STARTED WITH A BLEND OF THE OPERATIONAL 18Z GFS/12Z ECMWF WITH THE 18Z GEFS MEAN AND 12Z ECMWF ENSEMBLE MEAN FOR DAYS 3-5...SHIFTING TO GREATER WEIGHTING ON THE 18Z GEFS AND 12Z ECMWF ENSEMBLE MEANS DAYS 6-7. ...WEATHER HIGHLIGHTS... MOISTURE FROM TROPICAL STORM CINDY RIDES UP ALONG THE COLD FRONT...PRESENTING A HEAVY RAINFALL THREAT IN THE TN VLY INTO CNTRL-SRN APLCHNS DAY 3 SAT 24 JUN. EXPECT AREAS OF SHWRS/TSTMS AHEAD OF AND ALONG THE FRONT AS IT DRIFTS INTO/THROUGH THE SRN STATES NEXT WEEKEND INTO NEXT WEEK. THERE MAY ALSO BE SOME SHOWERS OVER THE GREAT LAKES AND VICINITY UNDER THE CORE OF THE UPR TROUGH AND AS AS SECONDARY WAVES CROSS THE REGION. A PERIOD OF LOW LVL UPSLOPE FLOW BEHIND THE MAIN FRONT MAY ENHANCE CONVECTION OVER THE SRN ROCKIES/HIGH PLAINS OF TX/NM IN THE EARLY TO MIDDLE PORTIONS OF NEXT WEEK. EXPECT THE HEAT OVER THE SOUTHWEST TO BECOME LESS EXTREME WITH TIME AS THE CORE OF THE RIDGE ALOFT OVER THE SOUTHWEST GRADUALLY SINKS SWD INTO MEXICO. HIGHS ARE FORECAST TO BE 10-15 F ABOVE NORMAL IN INTERIOR WA/OR CONTINUING INTO NV/ID DAYS 3-5...WITH HEIGHT FALLS LEADING TO A GRADUAL AIRMASS MODIFICATION TO LESS WARM VALUES DAYS 6-7. BELOW TO WELL BELOW NORMAL HIGH TEMPS OVER THE PLAINS LATE THIS WEEK INTO THE WEEKEND WILL SPREAD EWD TO LEAVE MUCH OF THE ERN HALF OF THE LOWER 48 WITH BELOW NORMAL READINGS BY NEXT SUN-TUE. THE AIRMASS RECOVERS SO THE PLAINS WARM TO ABOVE NORMAL VALUES BY THE MIDDLE OF NEXT WEEK. PETERSEN