EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1200 PM EDT SAT MAY 17 2014 VALID 12Z TUE MAY 20 2014 - 12Z SAT MAY 24 2014 ...GENERAL FLOW PATTERN AND MODEL DIFFERENCES... A COMPACT CLOSED LOW DIVING SOUTHEASTWARD INTO CALIFORNIA EARLY NEXT WEEK WILL SLOW DOWN AND OPEN UP AS IT MOVES INLAND OVER THE SOUTHWESTERN U.S. DURING THE MEDIUM RANGE PERIOD. THE DOWNSTREAM SUBTROPICAL RIDGE AMPLIFYING OVER THE SOUTH CENTRAL U.S. SHOULD PREVENT THE UPPER LOW/TROUGH FROM PROGRESSING VERY FAR EASTWARD THROUGH AT LEAST NEXT WEEKEND. NORTH OF THE BUILDING RIDGE...SHORTWAVE ENERGY WILL AMPLIFY WHILE TRACKING THROUGH THE NORTHERN PLAINS...GREAT LAKES...AND NEW ENGLAND...AND IS EXPECTED TO CLOSE OFF AN UPPER LOW BEFORE REACHING THE NORTHEAST COAST LATE NEXT WEEK. MODEL GUIDANCE IS IN VERY GOOD AGREEMENT WITH THE MEAN FLOW PATTERN ACROSS THE CONUS...EVEN OUT THROUGH DAY 7. DETERMINISTIC MODELS WERE SHOWING SOME SLIGHT DETAIL DIFFERENCES EARLY IN THE FORECAST PERIOD WITH THE EVOLUTION OF THE SHORTWAVE ENERGY CROSSING THE NORTHERN TIER...ESPECIALLY AS IT HELPS DEVELOP A SURFACE LOW OFF THE NORTHERN MID-ATLANTIC/NORTHEAST COAST NEXT WEDNESDAY/THURSDAY. ALSO...MODELS WERE BEGINNING TO SHOW SOME SPREAD WITH THE PROGRESSION OF THE UPPER LOW/TROUGH IN THE SOUTHWEST AND AMPLIFICATION OF THE DOWNSTREAM RIDGE OVER THE SOUTH CENTRAL U.S. BY THE END OF THE FORECAST PERIOD. THE GFS/GEFS MEAN WERE A BIT FASTER WITH BRINGING HEIGHT FALLS INTO THE SOUTHERN HIGH PLAINS WHEN COMPARED TO THE SLOWER ECMWF/ECMWF MEANS. A BLEND OF THE 00Z GEFS/ECMWF ENSEMBLE MEANS WAS USED FOR THE DAY 3-7 FORECAST SINCE IT SEEMED TO BEST RESOLVE THE SMALL DETAIL DIFFERENCES OVER THE NORTHERN TIER EARLIER IN THE FORECAST PERIOD...WHILE ALSO OFFERING A GOOD COMPROMISE WITH THE MODEL SPREAD IN THE PROGRESSION OF THE SOUTHWESTERN U.S. LOW/TROUGH LATE NEXT WEEK. ...SENSIBLE WEATHER HIGHLIGHTS... COOL AND UNSETTLED CONDITIONS ARE EXPECTED BENEATH THE CLOSED VORTEX DIVING THROUGH CALIFORNIA AND OPENING UP WHILE PROGRESSING INLAND OVER THE SOUTHWEST. AS THE HEIGHT FALLS GRADUALLY EDGE EAST AND MOISTURE SURGES OUT OF THE WESTERN GULF LATE NEXT WEEK...SOME MUCH NEEDED BENEFICIAL PRECIPITATION SHOULD DEVELOP OVER THE DROUGHT STRICKEN CENTRAL/SOUTHERN HIGH PLAINS. A BROAD AREA OF ABOVE NORMAL TEMPERATURES ARE EXPECTED WITH THE SUBTROPICAL RIDGE EXPANDING OVER THE SOUTH CENTRAL U.S....WHICH SHOULD IMPACT LOCATIONS FROM THE CENTRAL PLAINS TO THE SOUTHERN MID-ATLANTIC STATES. ACROSS THE NORTHERN TIER...SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE WITH THE SHORTWAVE AND RESULTING SURFACE SYSTEM TRACKING FROM THE UPPER MIDWEST TO THE NORTHEAST NEXT WEEK. AS AN UPPER 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 NEXT FRIDAY AND SATURDAY. GERHARDT