EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1241 PM EDT WED MAY 11 2016 VALID 12Z SAT MAY 14 2016 - 12Z WED MAY 18 2016 ...GENERAL FLOW PATTERN... A DEEP VORTEX SPINNING OVER SOUTHEAST CANADA WILL HELP SWEEP A COLD FRONT FROM THE UPPER MIDWEST TO THE MID-ATLANTIC AND NORTHEAST COAST THIS WEEKEND...BEFORE THE CORE OF THE VORTEX LIFTS TOWARDS THE CANADIAN MARITIMES EARLY NEXT WEEK. THE TAIL END OF THE BOUNDARY IS EXPECTED TO STALL ACROSS THE SOUTHERN TIER OF THE NATION...POTENTIALLY SURGING BACK NORTHWARD THROUGH THE SOUTHERN PLAINS...MIDDLE MISSISSIPPI VALLEY...AND OHIO/TENNESSEE VALLEYS NEXT MONDAY THROUGH WEDNESDAY. OUT WEST...AN UPPER LOW SHOULD SWING INTO THE PACIFIC NORTHWEST ON SATURDAY AND THEN TRANSITION TO A BROAD TROUGH PROGRESSING FROM THE WEST COAST TO THE ROCKIES EARLY NEXT WEEK. ...MODEL PREFERENCES/EVALUATION... DETERMINISTIC GUIDANCE WAS IN FAIRLY GOOD AGREEMENT WITH LARGE SCALE FEATURES ACROSS THE CONUS THIS WEEKEND...WITH THE EXCEPTION OF THE GFS BEING SLIGHTLY FASTER THAN THE ECWMF/ECMWF ENSEMBLE MEAN/GEFS MEAN CONSENSUS WITH THE TIMING OF THE COLD FRONT SWEEPING FROM THE UPPER MIDWEST TO THE EASTERN SEABOARD AND UPPER LOW SWINGING INTO THE PACIFIC NORTHWEST. DESPITE THE GENERAL AGREEMENT IN LARGE SCALE FEATURES...THERE IS STILL A LOT OF UNCERTAINTY WITH POSSIBLE CONVECTION DEVELOPING WITHIN ANOMALOUSLY HIGH MOISTURE SETTING UP ACROSS THE SOUTHERN PLAINS THIS WEEKEND. MODEL SPREAD BEGINS TO INCREASE ACROSS THE LOWER 48 NEXT TUESDAY AND WEDNESDAY...ESPECIALLY WITH THE EXACT INTERACTION/EVOLUTION OF THE BROAD UPPER TROUGH PROGRESSING OUT OF THE ROCKIES AND POSSIBLE CLOSED LOW DROPPING TOWARDS THE NORTH CENTRAL U.S.. THE WPC DAY 3-7 FORECAST STARTED WITH A BLEND OF THE GFS/ECMWF...WITH SLIGHTLY MORE WEIGHT TOWARDS THE ECMWF SINCE IT HAD MORE SUPPORT FROM ENSEMBLE MEAN GUIDANCE. BY EARLY NEXT WEEK...THE WPC FORECAST RELIED HEAVILY ON THE GEFS/ECMWF ENSEMBLE MEANS. ...SENSIBLE WEATHER HIGHLIGHTS... TEMPERATURES WILL STAY BELOW NORMAL BEHIND THE COLD FRONT SWEEPING FROM THE UPPER MIDWEST TO THE NORTHEAST AND MID-ATLANTIC COAST THIS WEEKEND. PRECIPITATION WILL BE POSSIBLE WITH THE PASSING FRONT...BUT THE GREATEST THREAT FOR HEAVY RAINS SHOULD BE NEAR THE TAIL END OF THE BOUNDARY AS IT STALLS OUT ACROSS THE SOUTHERN TIER AND POTENTIALLY INTERACTS WITH ANOMALOUSLY HIGH MOISTURE SETTING UP ACROSS THE SOUTHERN PLAINS THIS WEEKEND. THE CHANCE FOR HEAVY RAINS COULD EXPAND NORTH AND EAST ONCE THE BOUNDARY BEGINS TO SURGE BACK NORTHWARD NEXT TUESDAY AND WEDNESDAY. GERHARDT