EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1155 AM EDT SUN MAY 18 2014 VALID 12Z WED MAY 21 2014 - 12Z SUN MAY 25 2014 ...GENERAL FLOW PATTERN... A COMPACT CLOSED LOW MOVING IN OVER THE CENTRAL GREAT BASIN ON WEDNESDAY IS EXPECTED TO SLOW DOWN WHILE OPENING INTO A LONGWAVE TROUGH TOWARDS THE LATER HALF OF THE WEEK. A DOWNSTREAM UPPER RIDGE EXPANDING OVER THE SOUTH CENTRAL U.S. SHOULD KEEP THE TROUGH FROM EDGING TOO FAR EASTWARD OUT OF THE SOUTHWESTERN U.S. THROUGH AT LEAST THE BEGINNING OF NEXT WEEKEND. TO THE NORTH OF THE BUILDING RIDGE...SHORTWAVE ENERGY AMPLIFYING OVER THE GREAT LAKES ON WEDNESDAY SHOULD CLOSE OFF AN UPPER LOW BEFORE CROSSING INTO THE NORTHEAST LATE NEXT WEEK. ...MODEL PREFERENCES... MODEL GUIDANCE REMAINED IN UNUSUALLY GOOD AGREEMENT WITH THE MEAN FLOW PATTERN OVER THE CONUS FOR THE MEDIUM RANGE PERIOD...EVEN OUT TO DAY 7. NOTABLE DIFFERENCES EARLY IN THE FORECAST PERIOD WERE WITH THE ENERGY CROSSING THE NORTHERN TIER AND CLOSING OFF AN UPPER LOW BEFORE REACHING THE NORTHEAST...WHICH LEAD TO SOME SPREAD WITH THE RESPONDING SURFACE WAVE TRACKING TROUGH GREAT LAKES/SOUTHEAST CANADA AND SURFACE LOW DEVELOPING OFF OF THE NORTHEAST/NORTHERN MID-ATLANTIC COAST. THE 00Z ECMWF WAS A BIT MORE AMPLIFIED WITH THE SHORTWAVE AND STRONGER WITH THE SURFACE REFLECTION WHEN COMPARED TO THE 00Z GFS...BUT THE ECMWF HAD SUPPORT FROM THE UKMET AND HAS ALSO BEEN MORE CONSISTENT THAN THE GFS WITH THE EVOLUTION OF THIS FEATURE. TOWARDS THE END OF THE FORECAST PERIOD...ALTHOUGH THE GEFS/ECMWF ENSEMBLE MEANS WERE IN REMARKABLE AGREEMENT WITH THE PROGRESSION OF THE UPPER TROUGH OVER THE SOUTHWEST...A FAIR AMOUNT OF NOISE BETWEEN INDIVIDUAL ENSEMBLE MEMBERS INDICATES THERE IS STILL SOME UNCERTAINTY IN THE FORECAST. THE MEANS SHIFTED A BIT SLOWER WHEN COMPARED THEIR 00Z RUNS FROM YESTERDAY...AND TODAY'S DETERMINISTIC GUIDANCE ALSO HINTS AT A POSSIBLE SLOWER PROGRESSION THAN THE LATEST MEANS SUGGEST. A BLEND OF THE 00Z ECMWF/ECMWF ENSEMBLE MEAN WAS USED FOR THE DAY 3-7 FORECAST...WHICH SHOULD BEST REPRESENT THE SHORTWAVE/SURFACE FEATURE CROSSING THE NORTHERN TIER AND ACCOUNT FOR A POSSIBLE SLOWER PROGRESSION OF THE LONGWAVE TROUGH EDGING THROUGH THE SOUTHWEST. ...SENSIBLE WEATHER HIGHLIGHTS... COOL AND UNSETTLED CONDITIONS ARE EXPECTED BENEATH THE CLOSED SLOW MOVING IN AND OPENING UP OVER THE SOUTHWEST...BUT AS THE FEATURE GRADUALLY EDGES EASTWARD AND HEIGHTS BEGIN TO RISE BEHIND IT...ABOVE NORMAL TEMPERATURES WILL MAKE A RETURN TO THE WEST COAST. ABOVE NORMAL TEMPERATURES ARE ALSO EXPECTED WITH THE UPPER RIDGE BUILDING IN DOWNSTREAM...IMPACTING LOCATIONS FROM THE CENTRAL PLAINS TO THE SOUTHERN MID-ATLANTIC COAST. DROUGHT STRICKEN AREAS OF THE CENTRAL/SOUTHERN HIGH PLAINS SHOULD SEE SOME RELIEF LATE NEXT WEEK AS HEIGHT FALLS NUDGE OUT OF THE SOUTHWEST AND MOISTURE MAKES A RETURN OUT OF THE WESTERN GULF. ACROSS THE NORTHERN TIER...SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE WITH THE SHORTWAVE AND RESULTING SURFACE SYSTEM TRACKING FROM THE GREAT LAKES TO THE NORTHEAST. A SURGE OF BELOW NORMAL TEMPERATURES ARE EXPECTED IN THE SYSTEM'S WAKE...AND AS AN UPPER LOW LOW CLOSES OFF OVER NEW ENGLAND AND A SURFACE LOW DEVELOPS OFFSHORE...SOME WRAP AROUND PRECIPITATION WILL BE POSSIBLE ACROSS THE NORTHEAST AND NORTHERN MID-ATLANTIC REGION. GERHARDT