EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1226 PM EDT FRI MAY 20 2016 VALID 12Z MON MAY 23 2016 - 12Z FRI MAY 27 2016 ...PATTERN OVERVIEW... AN ANOMALOUS UPPER LOW CENTERED OVER THE MID-ATLANTIC STATES SHOULD BEGIN TO WEAKEN WHILE LIFTING NORTHEASTWARD ON MONDAY...BEFORE THE FOCUS SHIFTS TO A BROAD TROUGH CARVING OUT OVER THE WEST AND DOWNSTREAM RIDGE EXPANDING OVER THE EASTERN U.S. TOWARDS THE MIDDLE OF NEXT WEEK. BETWEEN THE TROUGH IN THE WEST AND RIDGE IN THE EAST...A STALLED FRONTAL BOUNDARY WILL REMAIN STRETCHED FROM THE SOUTHERN AND CENTRAL PLAINS TO THE UPPER MISSISSIPPI VALLEY. ...MODEL GUIDANCE/UNCERTAINTY ASSESSMENT... THERE IS STILL SOME UNCERTAINTY IN THE EXACT TIMING OF THE UPPER LOW LIFTING NORTHEASTWARD FROM THE MID-ATLANTIC STATES EARLY NEXT WEEK...BUT THE GREATEST SPREAD IN MODEL GUIDANCE CONTINUES TO BE OVER THE EASTERN PACIFIC WITH THE NEXT UPPER LOW APPROACHING THE WESTERN U.S. LATE NEXT WEEK. THE LATEST/00Z ECMWF ENSEMBLE MEAN SHIFTED SLOWER AND MORE TOWARDS THE GENERAL CLUSTERING OF THE GEFS/CMC/UKMET...AND EVEN DETERMINISTIC ECMWF...BUT THE ECMWF ENSEMBLE MEAN WAS STILL GIVEN LESS WEIGHT THAN NORMAL IN THE WPC DAY 3-7 FORECAST BECAUSE OF THE ALARMINGLY LARGE RUN-TO-RUN FLUCTUATIONS OVER THE EASTERN PACIFIC. GERHARDT ...SENSIBLE WEATHER HIGHLIGHTS... PRECIPITATION WILL FOCUS IN THE PACIFIC NORTHWEST, GENERALLY NORTHERN CALIFORNIA AND THE SIERRAS NORTHWARD AND ALSO EASTWARD THROUGH THE INTERMOUNTAIN WEST. BROAD SOUTHWEST FLOW ALOFT THROUGH THE CENTRAL PLAINS WILL KEEP A GOOD CHANCE OF SHOWERS/STORMS IN THE CENTRAL/SOUTHERN PLAINS THROUGH THE WEEK. SEVERE WEATHER MAY BE A POSSIBILITY ON ONE OR SEVERAL DAYS NEXT WEEK - PLEASE SEE THE LATEST SPC DAY 4-8 OUTLOOKS. TEMPERATURES WILL BE ON THE RISE IN THE EAST AFTER THE INITIAL COASTAL SYSTEM EXITS THE AREA MIDWEEK...WITH 70S AND 80S OVERSPREADING MOST OF THE EAST THURSDAY AND FRIDAY SOUTH OF THE FRONTAL BOUNDARY. MUCH OF THE MID-ATLANTIC WILL SEE HIGH TEMPS IN THE 80S FOR THE FIRST TIME THIS MONTH -- IT'S BEEN THE COOLEST START TO THE MONTH IN WASHINGTON DC (MAX TEMPS) SINCE 1917. THE WEST WILL GENERALLY BE COOLER THAN AVERAGE WITH ABUNDANT CLOUDS/SHOWERS EXCEPT FOR SOUTHERN CALIFORNIA EASTWARD THROUGH AZ INTO NM WHERE RAINFALL WILL BE NEARLY NON-EXISTENT BUT TEMPERATURES WILL STILL BE NEAR TO BELOW AVERAGE. FRACASSO