EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 226 AM EDT WED JUL 05 2017 VALID 12Z SAT JUL 08 2017 - 12Z WED JUL 12 2017 ...HOT ACROSS THE WEST & NORTHERN PLAINS FRIDAY AND SATURDAY... ...PATTERN/MODEL PREFERENCES... THE MODELS ARE IN BETTER THAN AVERAGE AGREEMENT ON THE PERSISTENCE OF THE CLOSED ANTICYCLONE OVER THE SOUTHWEST TO THE CENTRAL ROCKIES AND UPSTREAM CLOSED LOW OVER THE NORTHEAST PACIFIC AND DOWNSTREAM GREAT LAKES AND NORTHEAST UPPER LEVEL TROUGH. THE PRIMARY DIFFERENCES FOCUS ON TWO AREAS: THE FIRST IS THE AMPLITUDE OF THE EASTERN TROUGH...WITH THE 18Z GFS/GEFS FASTER DEAMPLIFYING THE TROUGH THAN THE 12Z ECMWF/ECMWF ENSEMBLE MEAN AND 12Z NAEFS ENSEMBLE MEAN. GIVEN THE PERSISTENCE OF THE UPSTREAM HIGH...THE PERSISTENCE OF THE DOWNSTREAM TROUGH IS PREFERRED AND THUS MORE WEIGHTING WAS GIVEN TO THE ECMWF ENSEMBLE MEAN AND 12Z NAEFS ENSEMBLE MEAN. THE ISSUE WITH THE 12Z ECMWF WAS THE DEVELOPMENT OF A WAVE NEAR HUDSON'S BAY SATURDAY AND SATURDAY NIGHT THAT DEVELOPS INTO A CLOSED LOW WHICH PLUNGES SOUTHEAST TO NORTH OF NY STATE AND MONTREAL QUEBEC BY 12Z TUE 11 JUL. THERE ARE FEW 12Z ECMWF ENSEMBLE MEMBERS AS AMPLIFIED AS THE OPERATIONAL RUN OR THAT DEVELOP A CLOSED LOW IN THE SAME AREA...SO THE OPERATIONAL 12Z ECMWF WAS NOT INCLUDED AFTER DAY 5 IN FAVOR OF THE BETTER CONTINUITY WITH THE ECMWF ENSEMBLE MEAN AND ITS COUNTERPARTS IN THE 18Z GEFS AND 12Z NAEFS MEANS. THE SECOND AREA OF DIFFERENCES IS IN WESTERN TO SOUTHERN CANADA AND THE NORTHERN ROCKIES TO THE PLAINS TO UPPER MS VALLEY. THE 12-18Z RUNS OF THE GFS BUCKLED NORTHWEST FLOW AND DEVELOPED A WAVE THAT RESULTED IN LOW PRESSURE IN THE NORTHERN PLAINS SUN TO LK SUPERIOR 12Z MON...WITH A TRAILING FRONT CROSSING THE LAKES MON INTO EARLY TUE. WITH THE GEFS MEMBERS SPLIT ON THE WAVE DEVELOPMENT AND A MINORITY IN THE ECMWF AND ECMWF ENSEMBLES...I WILL WAIT FOR A GREATER NUMBER OF OTHER SOLUTIONS TO INDICATE THE WAVE DEVELOPING LIKE THE GFS BEFORE COMMITTING TO IT. THE INITIAL CLOSED LOW IN THE NORTHEAST PACIFIC IS FORECAST BY MOST MODELS TO WEAKEN AND DRIFT INLAND...WITH THE FLOW DEAMLPLIFYING UNTIL A SECOND CLOSED LOW MOVES SOUTHEAST FROM THE ALEUTIANS TO TAKE ITS PLACE. THE 12Z ECMWF REFORMS A NEW CLOSED 700-5O0 MB LOW FURTHER INLAND IN WESTERN CANADA THAT BRINGS THE TROUGH FURTHER SOUTH ACROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES. WITH BETTER AGREEMENT AMONG THE ECMWF ENSEMBLE MEAN AND 18Z GFS/18Z GEFS MEAN/12Z NAEFS MEAN...THE FORECASTS USED THE MAJORITY CLUSTER AND NOT THE 12Z ECMWF. THE PRESSURES/FRONTS, 500 HPA HEIGHTS, AND WINDS WERE DERIVED FROM A BLEND OF THE DETERMINISTIC GFS/ECMWF AND THEIR CORRESPONDING MEANS (INCLUDING NAEFS) FOR DAYS 3-5. A BLEND OF THE 12Z ECMWF ENSEMBLE MEAN WITH LESS WEIGHT ON THE 12Z NAEFS MEAN AND 18Z GEFS MEAN WAS USED FOR DAYS 6 TUE 11 JUL AND DAY 7 WED 12 JUL. ...SENSIBLE WEATHER HIGHLIGHTS... SCATTERED RECORD HIGHS APPEAR LIKELY THIS COMING WEEKEND CENTERED OVER THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS/DESERT SOUTHWEST DUE TO THE STRONG RIDGE EXPECTED TO BE CENTERED OVER THE GREAT BASIN/INTERMOUNTAIN WEST. HIGHS OF 100-105F ARE EXPECTED THROUGH THE LOWER VALLEYS OF THE GREAT BASIN AND MONTANA PLAINS. A SYSTEM MOVING INTO THE PACIFIC NORTHWEST WILL LOWER HEIGHTS/TEMPS ALOFT AND LEAD TO DECREASING TEMPERATURES BACK TOWARDS SUMMERTIME NORMALS EARLY NEXT WEEK. IN THE EASTERN STATES, SHOWERS AND STORMS ARE FORECAST TO OCCUR ACROSS THE GREAT LAKES AND NORTHEAST WITH EACH FRONT THAT PROGRESSES ACROSS THESE AREAS. ACROSS THE SOUTHEAST, GULF COAST, AND FLORIDA, SCATTERED TO NUMEROUS MAINLY AFTERNOON/EVENING SHOWERS/STORMS WILL DEVELOP EACH DAY. A WAVY FRONT STALLED NEAR THE CAROLINA COASTLINE SHOULD ACT AS A FOCUS FOR SHOWER/STORM DEVELOPMENT. MONSOONAL MOISTURE ADVECTING INTO THE SOUTHWEST...CENTRAL AND SOUTHERN ROCKIES SHOULD SUPPORT WIDELY SCATTERED TO SCATTERED SHOWERS/STORMS DEVELOPING THROUGH THE PERIOD. RETURN MOISTURE ADVECTING NORTHWARD THROUGH THE PLAINS/MIDWEST SHOULD RESULT IN AN INCREASE IN SHOWERS/STORMS NEXT WEEK. PETERSEN/ROTH