EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1125 AM EDT THU MAY 15 2014 VALID 12Z SUN MAY 18 2014 - 12Z THU MAY 22 2014 ...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES... MODELS AND ENSEMBLES SHOW BETTER THAN AVERAGE AGREEMENT AND CONTINUITY FOR THE AMPLIFIED AND SLOWLY EVOLVING PATTERN EXPECTED DURING THE PERIOD. A TROUGH NEAR THE WEST COAST SHOULD STEADILY AMPLIFY WITH AN EMBEDDED UPR LOW SETTLING OVER/NEAR THE GRTBASIN BY THE MIDDLE OF NEXT WEEK. MEANWHILE AN UPR LOW CROSSING THE NORTHEAST EARLY NEXT WEEK SHOULD LINGER JUST OFF THE COAST INTO WED-THU... AT MOST REACHING THE CANADIAN MARITIMES. BETWEEN THESE FEATURES A RIDGE MAY BUILD TO THE MS VLY WITH A CLOSED HIGH PSBLY FORMING NEAR THE LWR MS VLY NEXT WED-THU. LATEST GFS/ECMWF AND THEIR ENSEMBLE MEAN RUNS HAVE BEEN FAIRLY STABLE AND NEAR THE MIDDLE OF THE GUIDANCE SPREAD FOR THE UPR LOW CROSSING THE NORTHEAST AND THEN LINGERING OFFSHORE. AHEAD OF THE AMPLIFYING WRN TROUGH THERE HAS BEEN A SOMEWHAT STRONGER TREND WITH ENERGY TRACKING ALONG/N OF THE US-CANADIAN BORDER AND BRUSHING THE EXTREME NRN PLAINS AROUND MON-TUE... WHILE THE WRN TROUGH SHOWS MORE TYPICAL RUN TO RUN VARIABILITY. GOOD CLUSTERING DAYS 3-5 SUN-TUE LEADS TO STARTING WITH A COMPOSITE BLEND OF THE 00Z GFS/ECMWF/UKMET. USED A GFS/ECMWF AND GFS/EC ENSEMBLE MEANS BLEND DAYS 6/7 IN A PERIOD WITH DECENT COMPATABILITY BUT SLOWLY INCREASING FORECAST SPREAD. ...SENSIBLE WEATHER HIGHLIGHTS... WE STILL EXPECT THE AMPLIFYING WRN TROUGH AND DOWNSTREAM FLOW TO SPREAD MSTR AND COOLER THAN NORMAL DAYTIME TEMPS ACROSS THE NRN HALF OF THE WEST COAST THROUGH THE GRTBASIN... ROCKIES... NRN PLAINS... AND INTO THE GRTLKS. COMBINATION OF DYNAMICS ALOFT/SLOWING OF THE UPR SYSTEM AND TERRAIN ENHANCEMENT FROM THE HIGH PLAINS WWD MAY SUPPORT MDT-HVY PCPN AT SOME LOCATIONS. THE EXTREME NRN TIER MAY ALSO SEE A PERIOD OF HEAVIER RNFL AROUND MON-WED IN ASSOC WITH THE MID LVL SYSTEM TRACKING ALONG/N OF THE CANADIAN BORDER. MEANWHILE SOME SHWRS/TSTMS MAY DEVELOP FARTHER SEWD AS A SRN PLAINS WARM FRONT LIFTS NEWD TOWARD THE OH VLY. THE UPR LOW AFFECTING THE NORTHEAST WILL SUPPORT COOLER THAN AVG HIGHS AND SCT AREAS OF RNFL MOST DAYS. GREATEST ANOMALIES FOR TEMPS SHOULD BE OVER THE SRN HALF OF THE PLAINS WITH LOCATIONS FROM WRN TX INTO KS SEEING THE BEST POTENTIAL FOR HIGHS OF 10-20F ABOVE NORMAL FOR ONE OR MORE DAYS IN THE MON-WED TIME FRAME... PSBLY APPROACHING DAILY RECORD VALUES. SOME OF THIS WARMTH WILL SPREAD EWD WITH TIME THOUGH WITH LESSER ANOMALIES. DAYTIME HIGHS UPWARDS TO 10F BELOW NORMAL OVER THE WEST SHOULD BE MORE LOCALIZED AND UNDER THE GRTBASIN UPR LOW TUE-WED. SCHICHTEL