EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 209 AM EDT SAT SEP 06 2014 VALID 12Z TUE SEP 09 2014 - 12Z SAT SEP 13 2014 ...NORBERT MOISTURE SPREADS OUT FROM THE SOUTHWEST NEXT WEEK AS LEAD COLD CANADIAN AIR DIGS FROM NWRN US AND ROCKIES INCREASINGLY THROUGH THE CENTRAL AND ERN US... ...PATTERN OVERVIEW... PERSISTENT UPPER-LEVEL RIDGING ALONG THE WEST COAST OF CANADA AND EASTERN GULF OF ALASKA PRODUCES AN AMPLIFIED PATTERN DOWNSTREAM IN THE CENTRAL PORTION OF THE NORTH AMERICAN CONTINENT. MID-PERIOD---REMNANT NORBERT MID-LEVEL MOISTURE STREAKS INTO THE BASE OF THE UPPER-LEVEL TROUGH AND PROCEEDS DOWNSTREAM ACROSS THE CENTRAL PLAINS THEN EAST-CENTRAL US. MID-LEVEL MOISTURE ASSOCIATED WITH NORBERT WILL FUEL PREDECESSOR EARLY PERIOD RAINS THAT MIGRATES DOWNWIND OVER THE SOUTHWEST. BY TUE...THE MIGRATION OF AN UPPER-LEVEL TROUGH ALONG 125W WILL IMPINGE A DRIER AIRMASS UPON THE NORTHERN PERIPHERY OF NORBERT CLOUD SHIELD AND PROVIDE THE UPPER-LEVEL STEERING MECHANISM FOR DOWNSTREAM SUBTROPICAL MOISTURE TRANSPORT. BEHIND THE EXITING WRN US TROUGH...A SIGNIFICANT UPSTREAM NRN STREAM SHORTWAVE DESCENDS THE CANADIAN ROCKIES AND FORMS A DEEPER...COLDER AND MORE UNSTABLE UPPER-LEVEL TROUGH OVER THE UPPER MIDWEST AND SOUTH CENTRAL CANADA BY LATE NEXT WEEK...THEN NERN/ERN US NEXT SATURDAY. ...GUIDANCE/UNCERTAINTY ASSESSMENT... THE 18 UTC GFS/GEFS MEAN AND 00 UTC ECMWF AND 00 UTC ECMWF/NAEFS ENSEMBLE MEANS HAVE CONVERGED UPON THIS GENERAL FLOW AND MASS FIELD MEDIUM RANGE EVOLUTION...BOLSTERING FORECAST CONFIDENCE. ACCORDINGLY...WPC MEDIUM RANGE PRODUCTS HAVE BEEN PRIMARILY DERIVED FROM A BLEND OF THESE COMPATABLE GUIDANCE SOURCES ALONG WITH CONTINUITY. ...SENSIBLE WEATHER HIGHLIGHTS... CONSIDERABLY COLDER CANADIAN HIGH PRESSURE MIGRATING SOUTHEASTWARD AND SPREADING OUT ACROSS MUCH OF THE LOWER 48 NEXT WEEK. AN UPSLOPE FLOW COMPONENT APPEARS TO RETURN IN EARNEST ALONG THE DIVIDE AND DOWN THE EASTERN SLOPES OF THE ROCKIES. RESIDUAL 'NORBERT' MID-LEVEL MOISTURE WILL BE INFLUENTIAL IN GENERATING A VARIED OVER-RUNNING ENVIRONMENT...WITH AMPLE CONVECTION ALSO ALONG/AHEAD THE MAIN FRONT. DOWNSTREAM...WPC PROGS HOLD ONTO A ERN US SURFACE WEDGE INTO MIDWEEK AND ALLOW A MOIST WAVE TO CARRY DOWNWIND INTO THE WRN ATLANTIC. THIS ALLOWS COOLER AND WETTER WEATHER TO LINGER MAINLY FROM SERN US AND MID-ATLANTIC COAST LINE INTO NEW ENGLAND PRIOR TO LATER NEXT WEEK UPSTREAM FLOW AMPLIFICATION AND FRONTAL APPROACH. SCHICHTEL