EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 958 AM EST SUN NOV 29 2015 VALID 12Z WED DEC 02 2015 - 12Z SUN DEC 06 2015 ...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES... OUT WEST...THE MODELS/ENSEMBLES STILL ADVERTISE THE HIGH AMPLITUDE DEEP LAYER RIDGE WED-THU AND THEN THE APPROACH OF AN UPPER TROUGH TO THE WEST COAST LATE THU...MOVING ONSHORE AND INLAND INTO THE GREAT BASIN FRI AND CENTRAL TO SOUTHERN ROCKIES SAT...EMERGING ON TO THE SOUTHERN PLAINS SUNDAY 06 DEC. THE MODELS HAVE TYPICAL TIMING/AMPLITUDE/PHASING DIFFERENCES. THE 06Z RUNS OF THE GFS AND GEFS MEAN HAVE AMPLIFIED THE 500 MB TROUGH NEXT WEEKEND. WITH THE GEFS MEAN SHOWING FASTER TIMING OF THE TROUGH WITH BETTER AGREEMENT AMONG THE ECMWF AND CANADIAN ENSEMBLE MEANS...LESS WEIGHTING WAS GIVEN TO THE 00Z GEFS MEAN TO ADDRESS THE TYPICAL FAST BIAS OF THE GEFS. THE SAME IDEA APPLIES TO THE NORTHERN STREAM PORTION OF THE TROUGH AS IT CROSSES THE NORTHERN ROCKIES FRI AND OUT ON TO THE PLAINS SAT 05 DEC...WITH THE GFS SHOWING A SLIGHTLY FASTER FORWARD PROGRESSION THAN THE 00-06Z GEFS/00Z CANADIAN/00Z ECMWF ENSEMBLE MEANS...WHICH CLUSTER WELL. AS A LARGE AND INTENSE STORM WINDS UP IN THE NORTHEAST PACIFIC HEIGHTS REBOUND SMARTLY IN THE PACIFIC NORTHWEST AND NORTHERN CA NEXT FRI-SAT AS A RIDGE BUILDS DOWNSTREAM FROM THE CYCLONE. THE ECMWF/CANADIAN ENSEMBLES SHOW THE UPPER TROUGH APPROACHING AND DEAMPLIFYING AS IT MOVES ONSHORE SUN 06 DEC. A POSITIVE HEIGHT ANOMALY IN CENTRAL CANADA EXTENDS ROUTINELY DOWN INTO THE NORTHERN PLAINS/UPPER MS VALLEY/GREAT LAKES. CONSEQUENTLY IN THE EAST...THE MODELS ARE IN GOOD AGREEMENT DAYS 3-EARLY DAY 4 WITH THE CLOSED 500 MB LOW CROSSING THE LAKES AND MOVING DOWN THE ST LAWRENCE VALLEY AND EXITING OFF THE NEW ENGLAND COAST. THE SCENARIO GETS REPEATED ON DAYS 6-7 WITH THE NORTHERN STREAM TROUGH CROSSING THE NORTHERN PLAINS SAT INTO THE UPPER LAKES SUN 06 DEC WITH THE OPERATIONAL RUN MORE AMPLIFIED THAN CONTINUITY AND/OR THE ECMWF ENSEMBLE MEAN. THE 0Z ECMWF HAS POOR RUN TO RUN CONTINUITY AND DIFFERENCES FROM THE OPERATIONAL MODEL VS THE ENSEMBLE MEAN AS THE 00Z RUN AMPLIFIED A WAVE EXITING THE NORTHERN PLAINS THU AS IT MOVES ACROSS THE UPPER MS VALLEY AND THEN THE GREAT LAKES FRI AND NY/NEW ENGLAND SAT. THE ENSEMBLE MEANS IS LESS AMPLIFIED AND DOES NOT DEVELOP A CLOSED LOW LIKE THE OPERATIONAL RUN. AT THE SAME TIME THE ECMWF DEVELOPS A CLOSED 500 MB OVER NY THE 06Z GFS DEVELOPS A CLOSED HIGH. THE GEFS MEAN SHOWS A RIDGE CROSSING NY/NEW ENGLAND OVER THE WEEKEND...WITH THE ECMWF ENSEMBLE MEAN SHOWING THE TROUGH MOVING OFF THE COAST FASTER THAN THE OPERATIONAL ECMWF AND BUILDING A RIDGE ACROSS THE AREA CLOSER TO THE 00-06Z GEFS AND NAEFS MEANS. ACROSS THE SOUTHEAST TO THE MID ATLANTIC COAST...THE 06Z GFS WAS AN OUTLIER BUILDING A CLOSED 500 MB LOW NEAR THE TN/NC BORDER 00Z SAT. THE ENSEMBLE MEANS HOWS AN OPEN WAVE LIKE OTHER SOLUTIONS BUT THEN THE GEFS MEAN MOVES THE TROUGH OUT OF THE SOUTHEAST FASTER THAN THE ECMWF AND CANADIAN MEANS DO. CONSEQUENTLY...A BLEND OF THE 00Z NAEFS AND ECMWF ENSEMBLE MEANS WAS USED FOR THE FORECAST DAYS 3-7. ...SENSIBLE WEATHER HIGHLIGHTS... RAIN IS EXPECTED WED IN NEW ENGLAND AND WINDING DOWN THURSDAY AFTERNOON AS THE UPPER LOW DEPARTS. THE TAIL END OF THE COLD FRONT SLOWLY SINKS THROUGH FLORIDA WHERE MORE APPRECIABLE RAIN IS POSSIBLE. MODERATE TO HEAVY RAIN IS EXPECTED FROM NORTHERN CA/WESTERN OR-WA COAST WED-FRI. MORE RAINS ARE EXPECTED IN WESTERN WA SAT-SUN WITH THE SYSTEM NEXT WEEKEND. THE FIRST SYSTEM WILL SPLIT OFF THROUGH THE FOUR CORNERS REGION WITH BRIEFLY COOLER TEMPERATURES AND LIGHT RAIN/SNOW FOR NV/UT/CO AND INTO NM AS THE SURFACE LOW EXITS ONTO THE SOUTHERN PLAINS. SHOWER COVERAGE PICKS UP IN THE SOUTHERN PLAINS TO LOWER MS VALLEY AS RETURN FLOW FROM THE GULF OF MEXICO SUPPLIES INCREASING MOISTURE INTO THE SYSTEM. TEMPERATURES WILL BE ABOVE AVERAGE -- BY ABOUT 10-15 DEGREES -- ACROSS THE NORTHERN PLAINS DAYS 4-7. NO ARCTIC AIR INTRUSIONS ARE EXPECTED. TEMPERATURES ARE FORECAST TO BE A FEW DEGREES BELOW AVERAGE FROM TEXAS TO THE LOWER MS VALLEY AND THEN THE SOUTHEAST. PETERSEN