EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1033 AM EDT SAT AUG 08 2015 VALID 12Z TUE AUG 11 2015 - 12Z SAT AUG 15 2015 ...OVERVIEW AND EVALUATION/PREFERENCES...... A CLOSED MID LEVEL ANTICYCLONE IS FORECAST TO DRIFT WEST OUT OF THE SOUTHERN PLAINS ACROSS THE SOUTHERN ROCKIES INTO THE SOUTHWEST US. FURTHER WEST A CLOSED LOW OFF THE CA COAST GRADUALLY WEAKENS AND EJECTS INTO THE NORTHWEST AND NORTHERN ROCKIES...REACHING THE NORTHERN PLAINS BY THE END OF THE PERIOD. A TROUGH PERSISTS IN THE EASTERN US. THE 00Z-06Z GFS/00Z ECMWF ARE SUFFICIENTLY SIMILAR TO EACH OTHER AND THEIR MEANS TO ALLOW A CONSENSUS APPROACH TO BE USED...WITH SLIGHTLY GREATER WEIGHTING OF THE MODELS THROUGH DAY 5 AND SLIGHTLY MORE WEIGHTING OF THE ENSEMBLE MEANS DAYS 6-7. ...WESTERN US TO THE NORTHERN PLAINS... THE 00Z-06Z GFS/00Z ECMWF AND THEIR 00Z ENSEMBLE MEANS SHOW A CLOSED 500 MB LOW OFF THE OR/ADJACENT NORTHERN CA COASTS TUE AND WED 12 AUG AND THEN WEAKENING AS THE TROUGH EJECTS NEWD AS NERN PAC SHRTWV ENERGY APPROACHES. THE 00-06Z GFS ARE MORE AMPLIFIED WITH THE EJECTING WAVE ACROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES VS THE ECMWF. A SFC BNDRY MAY DROP INTO THE NRN HIGH PLAINS DAY 5 SOUTH OF CANADIAN LOW PRESSURE TIME BEFORE LOW PRES DEVELOPS IN THE NORTHERN ROCKIES AND MOVES THE FRONT BACK NORTH WITH A COLD FRONT MOVING EAST FROM THE NORTHERN ROCKIES DAY 6 ONTO THE PLAINS DAY 7. THE 00Z-06Z GFS ARE MORE AMPLIFIED ALOFT AND BRINGS THE LEADING FRONT FARTHER S/SE THAN THE 00Z ECMWF/00Z CANADIAN AND THEIR RESPECTIVE ENSEMBLE MEANS OVER THE NORTHERN PLAINS DAYS 6-7. THE 00Z GEFS MEAN IS LESS AMPLIFIED THAN THE GFS AND CLOSE IN AGREEMENT TO THE ECMWF ENSEMBLE MEAN TROUGH AMPLITUDE. THE 00Z ECMWF ALSO BUILDS THE 500 MB ANTICYCLONE FURTHER WEST ACROSS THE SOUTHWEST US THAN ITS ENSEMBLE MEAN AND THE 00Z GFS/CANADIAN GLOBAL AND THEIR ENSEMBLE MEANS. TELECONNECTIONS WITH THE TROUGH OVER KAMCHATKA TROUGH PERSISTENT LOWER HEIGHTS OFF THE WEST COAST...WHICH LEAN AGAINST THE HIGH CONTINUING TO BUILD WEST. CONSEQUENTLY...LOWER WEIGHTING WAS GIVEN TO THE OPERATIONAL 00Z ECMWF DAY 7...SAT 15 AUG. ...EASTERN US... LEADING ERN TROUGH ENERGY WILL BRING AN AREA OF LOW PRESSURE FROM THE LOWER GREAT LKS/OH VLY THROUGH THE NORTHEAST... WITH TRIPLE POINT LOW REDEVELOPMENT JUST OFF THE NJ COAST 00Z WED WITH THE NEW LOW CENTER MOVING ADJACENT TO THE NEW ENGLAND COAST 12Z WED AND NEAR NEW BRUNSWICK BY 00Z THU. A WAVY FRONT THEN TRAILS SOUTH ACROSS THE EASTERN CAROLINAS AND SOUTHERN GA WITH GOOD CLUSTERING OF SOLUTIONS. THE FRONT SLOWLY DISSIPATES OVER THE WEEKEND ON THE SOUTHEAST/EASTERN GULF COAST OVER THE WEEKEND. A CONSENSUS OF THE 06Z/00Z ECMWF AND THEIR ENSEMBLE MEANS WAS USED. THE 00Z GFS WAS AN OUTLIER SHOWING A CLOSED 500 MB LOW DEVELOPING NEAR THE ONTARIO/QUEBEC BORDER 00Z SAT AND MOVING INTO QUEBEC SAT. THE 06Z GFS RUN BACKED OFF THE CLOSED LOW WITH A MORE PROGRESSIVE WAVE THAT AGREES BETTER WITH THE THE 00Z ECMWF AND ITS ENSEMBLE MEAN...AS WELL AS THE 00-06Z GEFS MEAN...SO THE 06Z GFS WAS USED INSTEAD OF THE 00Z RUN. ...SENSIBLE WEATHER HIGHLIGHTS... SFC LOW PRES ACROSS NEW ENGLAND TUE 11 AUG SUPPORTS A PERIOD OF SHOWERS AND RAIN DAY 3. THE TRAILING FRONT MAY ALSO BE ACCOMPANIED BY SOME AREAS OF ENHANCED RAINFALL IN FLORIDA... WITH MULTIPLE DAYS OF SHOWERS/STORMS PSBL OVER FL AS THE SRN PART OF THE FRONT STALLS. UPR LOW NEAR THE WEST COAST SHOULD SUPPORT SOME SCT RNFL WITH A MORE ORGANIZED EVENT PSBL ONCE IT EJECTS NEWD. THIS SYSTEM AND LEADING FRONT NEAR THE US-CANADIAN BORDER MAY GENERATE SCT CONVECTION OVER PARTS OF THE NRN TIER THU-SAT. MEANWHILE EXPECT PERIODS OF CONVECTION IN MONSOONAL FLOW IN THE SOUTHERN TO CENTRAL ROCKIES. THE UPPER TROUGH MOVING ONSHORE WITH THE EJECTING WEST COAST UPR LOW SHOULD RESULT IN SOME BELOW NORMAL TEMPERATURES DEVELOPING AS WELL. TEMPERATURES TRANSITION FROM ABOVE NORMAL IN THE PACIFIC NORTHWEST DAY 3 AND 4 TO BELOW NORMAL DAY 5...THU 13 AUG. PETERSEN/RAUSCH