EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1025 AM EDT WED SEP 27 2017 VALID 12Z SAT SEP 30 2017 - 12Z WED OCT 04 2017 ...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES... PATTERN EVOLUTION SAT-WED WILL DEPEND ON HOW THE UPSTREAM NORTH PACIFIC OCEAN EVOLVES DURING THE NEXT FEW DAYS. THIS HAS BEEN UP FOR DEBATE AMONG THE MODELS/ENSEMBLES FOR SEVERAL DAYS RUNNING. ENSEMBLES HAVE HAD LESS CONSISTENCY THAN NORMAL, WITH THE DETERMINISTIC MODELS EVEN WORSE. THE ECMWF ENSEMBLE MEAN HAS SHOWN BETTER CONTINUITY IN THE WESTERN CONUS/EASTERN PACIFIC) SO ONCE DIFFERENCES DEVELOP ON DAY 5...INCREASED WEIGHTING WAS GIVEN TO THE ECMWF ENSEMBLE MEAN UNTIL THE DAY 7 WED 04 OCT FORECAST...AT WHICH POINT THE ECMWF ENSEMBLE MEAN WAS USED AS A MIDDLE OF THE ROAD SOLUTION BETWEEN FASTER CANADIAN ENSEMBLE MEAN AND SLOWER 06Z GEFS MEAN...WHICH BRINGS THE TROUGH ONSHORE SEVERAL HOURS SLOWER THAN THE ECMWF MEAN EARLY NEXT WEEK. DAYS 3-5 USED A BLEND OF THE 06Z GFS/06Z GEFS MEAN AND 00Z ECMWF/ECMWF ENSEMBLE MEAN. MINOR TIMING/AMPLITUDE DIFFERENCES EXIST WITH THE EXITING NORTHEAST TROUGH AND THE DEVELOPING INTERIOR NORTHWEST TROUGH. AFTER THAT, ENSEMBLES DIVERGE ON THE REINFORCING TROUGH DEVELOPING ON MONDAY WITH THE ECMWF ENSEMBLES LOWERING HEIGHTS MORE QUICKLY THAN THE CANADIAN ENSEMBLES WITH THE GEFS ENSEMBLES LAGGING WELL BEHIND NEAR THE SOUTHWEST COAST OF CANADA ON MONDAY 02 OCT. THE ENSEMBLE MEANS AGREE ON UPSTREAM RIDGING IN ALASKA...WHICH TELECONNECTS TO A PACIFIC NORTHWEST TROUGH. THE 00Z ECMWF FLIPPED TO A CLOSED LOW FURTHER SOUTH THAN THE MODEL MAJORITY 12Z WED NEAR THE CA/OR BORDER. SINCE TELECONNECTIONS SHOW A MORE OPEN TROUGH CENTERED FURTHER NORTH...MORE WEIGHTING WAS GIVEN TO THE MEANS...WHICH AVOIDS TRYING TO COMMIT TO A CHANGING OPERATIONAL SOLUTION. THE ENSEMBLES AGREE ON UPPER RIDGING EXPANDING IN THE SOUTHEAST/TN VALLEY NEXT WEEK. THIS WILL SLOW THE FRONTAL PROGRESSION IN THE NORTHERN PLAINS TO UPPER MS VALLEY WAITS FOR THE REINFORCING TROUGH TO PROVIDE A SURGE OF COLD ADVECTION TO MOVE THE FRONT EAST. ...WEATHER HIGHLIGHTS... PRECIPITATION WILL FOCUS ACROSS FLORIDA NEAR THE SLOWLY MOVING COLD FRONT THAT SHOULD EVENTUALLY STALL AND DISSIPATE BY THE MIDDLE OF NEXT WEEK. EASTERLY FLOW AND ABOVE AVERAGE PRECIPITABLE WATER VALUES SUPPORTS RAINS WITH LOCALLY HEAVY AMOUNTS. PAC NW WILL SEE BOUTS OF RAIN AND MOUNTAIN SNOW WITH EACH UPPER/SFC SYSTEM WITH ADDITIONAL RAIN FARTHER EAST OVER THE NORTHERN PLAINS INTO THE UPPER MIDWEST AS THE LEAD FRONT MOVES SLOWLY EASTWARD AND NORTHEASTWARD. A DRY PERIOD IS EXPECTED UNDER THE DEVELOPING UPPER HIGH IN THE OH VALLEY/TN VALLEY/INTERIOR SOUTHEAST. BELOW NORMAL TEMPERATURES DEVELOP AND PERSIST ACROSS THE PACIFIC NORTHWEST/NORTHERN ROCKIES/NORTHERN HIGH PLAINS...WITH DAYS WHERE READING ARE NEAR 10 DEGREES BELOW NORMAL. LIKEWISE...THE BUILDING ANTICYCLONE IN THE OH VALLEY TO TN VALLEY RESULTS IN TEMPERATURES RISING ABOVE NORMAL WITH AREAS IN THE GREAT LAKES TO UPPER OH VALLEY NEAR 10 DEGREES ABOVE NORMAL EARLY TO MIDDLE PORTIONS OF NEXT WEEK. WITH THE HIGH MOVING OFF THE COAST...ABOVE NORMAL TEMPERATURES SPREAD INTO NY/PA/NEW ENGLAND. PETERSEN/FRACASSO