EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1200 PM EDT THU SEP 25 2014 VALID 12Z SUN SEP 28 2014 - 12Z THU OCT 02 2014 ...OVERVIEW... THE PATTERN ACROSS THE CONUS WILL BE RATHER BLOCKED IN NATURE AS A STRONG CLOSED LOW OCCUPIES THE SOUTHWESTERN U.S. THE 00Z GFS FORECAST ANOMALIES SUGGEST THE 500-MB HEIGHTS WILL BE APPROXIMATELY 2 STANDARD DEVIATIONS BELOW CLIMATOLOGY BEGINNING EARLY SUNDAY. THIS ANOMALY SHOULD GRADUALLY DIMINISH IN TIME AS THE UPPER LOW POTENTIALLY EVOLVES INTO MORE OF AN OPEN WAVE ACROSS THE INTERMOUNTAIN WEST/ROCKY MOUNTAIN REGION. THE OTHER FEATURE OF INTEREST WHICH WILL BE CUT OFF FROM THE PREVAILING WESTERLIES IS A SLOW-MOVING WEAKNESS ACROSS THE MIDDLE TO LOWER MS VALLEY. BOTH OF THESE SYSTEMS ARE EXPECTED TO DRAG EASTWARD AT A RELATIVELY SLOW PACE DURING THE FIRST COUPLE DAYS OF THE PERIOD. THE PATTERN BECOMES MORE PROGRESSIVE BEYOND DAY 4/MONDAY AS THE NORTHERN STREAM BEGINS TO IMPACT THE MID-LATITUDES. AN UPPER TROF DESCENDING FROM THE NORTHEASTERN PACIFIC EARLY MONDAY SHOULD EVENTUALLY REACH THE PACIFIC NORTHWEST BY DAY 5/TUESDAY HELPING TO EVENTUALLY ESTABLISH A LONGWAVE TROF ACROSS THE WESTERN HALF OF THE COUNTRY THROUGH THE MIDDLE OF NEXT WEEK. AN ADDITIONAL NORTHERN STREAM SYSTEM MAY IMPACT THE GREAT LAKES ON MONDAY/TUESDAY BUT THAT APPEARS MUCH MORE NEBULOUS. ...GUIDANCE EVALUATION/PREFERENCES... EARLY IN THE FORECAST...THE GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH THE PLACEMENT OF THE UPPER CYCLONE IN THE SOUTHWESTERN U.S. IT IS WORTH NOTING THE GFS SUITE OF SOLUTIONS ARE A TAD WEAKER ALOFT WHILE THE 576-DM SPAGHETTI PLOT INDICATES SOME OF THE 00Z ECMWF ENSEMBLE MEMBERS ARE SLIGHTLY FASTER. AS THE CLOSED LOW EVENTUALLY OPENS UP ACROSS THE ROCKIES/HIGH PLAINS EARLY NEXT WEEK...THE 00Z ECMWF ENSEMBLE MEMBERS CONTINUE TO FAVOR SOMETHING A LITTLE QUICKER THAN THE SLOWER/FLATTER 00Z GEFS MEMBERS. THE BIGGER DIFFERENCES ARISE LATER ON IN THE PERIOD WITH REGARDS TO HOW QUICKLY THE UPSTREAM SYSTEM MOVES INTO THE WESTERN U.S. THE 06Z GEFS MEAN APPEARS TO BE THE OUTLIER HERE WITH THE PLACEMENT OF THE LONGWAVE TROF ON DAYS 6 AND 7/WEDNESDAY AND THURSDAY. IT PORTRAYS A TROF AXIS WHICH IS FARTHER INLAND THAN THE MORE CLUSTERED 00Z ECMWF/CMC/NAEFS ENSEMBLE MEANS. LOOKING DOWNSTREAM...THE 00Z ECMWF/GFS/UKMET ARE REASONABLY CLUSTERED ON DAY 3 WHILE THE 06Z GFS SEEMED TO DIVERGE MORE SIGNIFICANTLY FROM THOSE SOLUTIONS. THE SPREAD BETWEEN THE GFS/ECMWF HAS DIMINISHED RELATIVE TO THE SPREAD YESTERDAY WHICH RAISED CONFIDENCE IN KEEPING DETERMINISTIC GUIDANCE IN THE BLEND THROUGH DAY 4. FOLLOWED A COMBINATION OF THE 00Z ECMWF/GFS ON DAYS 3/4 WITH A SMALL PORTION OF THE 00Z UKMET ADDED ON DAY 3. EVENTUALLY HAD TO RULE OUT THE 00Z GFS AS ITS PAST FEW RUNS HAVE OVERDEVELOPED THE SYSTEM EMERGING FROM THE NORTHERN STREAM IN THE VICINITY OF THE GREAT LAKES. GIVEN THE AFOREMENTIONED MORE PROGRESSIVE NATURE OF THE 06Z/00Z GEFS MEAN IN THE WESTERN U.S...FAVORED AN EQUAL BLEND OF THE 00Z ECMWF/NAEFS ENSEMBLE MEANS FOR THE LATTER HALF OF THE FORECAST. ...SENSIBLE WEATHER HIGHLIGHTS... THE SLOW-MOVING UPPER TROF IN THE WESTERN U.S. WILL FAVOR ABOVE NORMAL TEMPERATURES ACROSS MUCH OF THE CENTRAL TO NORTHERN STATES WITH ANOMALIES POTENTIALLY REACHING 1O TO 15 DEGREES ABOVE NORMAL. MEANWHILE...THE BELOW NORMAL HEIGHT IN THE WEST WILL KEEP CONDITIONS COOLER THAN CLIMATOLOGY WITH AN ABUNDANCE OF PRECIPITATION ACROSS THE MOUNTAINS AND ALONG THE SLOW-MOVING FRONTAL BOUNDARY. ELSEWHERE...HEAVY RAINFALL IS POSSIBLE ACROSS THE SOUTHEASTERN U.S. AHEAD OF THE WEAKNESS IN THE MID-LEVEL FLOW COMBINED WITH A WARM FRONT LIFTING OUT OF THE GULF OF MEXICO. RUBIN-OSTER