EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 238 AM EDT WED MAY 18 2016 VALID 12Z SAT MAY 21 2016 - 12Z WED MAY 25 2016 ...PATTERN OVERVIEW... EXPECT MEAN TROUGHING TO PERSIST NEAR THE WEST COAST AS MULTIPLE PIECES OF ENERGY FROM THE NERN PAC TAKE THE PLACE OF INITIAL ENERGY FCST TO EJECT NEWD ACROSS THE WEST AND THEN THE NRN PLAINS. MEANWHILE AN UPR TROUGH WILL LIKELY CLOSE OFF A LOW NEAR THE EAST COAST BY DAY 5 MON WITH THE MOST PROBABLE TRACK HAVING THE UPR LOW REACHING NEW ENGLAND BY MIDWEEK. OVERALL PREDICTABILITY SHOULD BE GREATER WITH THE LARGER SCALE EAST COAST SYSTEM IN CONTRAST TO THE MULTIPLE INDIVIDUAL FEATURES COMPRISING THE WRN MEAN TROUGH. ...GUIDANCE EVALUATION... WITHIN THE WRN MEAN TROUGH GUIDANCE SEEMS TO BE FINDING SOME COMMON THEMES BUT INDIVIDUAL MODEL RUNS AND ENSEMBLE MEMBERS SUFFICIENTLY DIVERGE TO TEMPER CONFIDENCE IN ANY SPECIFIC SOLN. MODELS AND ENSEMBLE MEANS ARE NOW CLUSTERING BETTER WITH A SIGNIFICANT BUNDLE OF ENERGY IN THE CORE OF THE INITIAL WRN TROUGH EJECTING INTO THE NRN PLAINS BY DAY 5 MON AND SUPPORTING A FAIRLY VIGOROUS SFC LOW AT THAT TIME. WITH SOME VARIABILITY THE GENERAL TREND WITH THIS FEATURE HAS BEEN TOWARD FASTER TIMING OVER THE PAST DAY OR SO. AT THE MOMENT THERE IS A CONSIDERABLE MAJORITY CLUSTER SUGGESTING THAT THE 12Z ECMWF MAY BECOME TOO SLOW. GENERAL EVOLUTION OF THE MEAN PATTERN TOWARD SWLY FLOW ALOFT DOWNSTREAM FROM THE WRN STATES SEEMS TO FAVOR AT LEAST SOMEWHAT GREATER PROGRESSION THAN SEEN IN THE 12Z ECMWF. BEHIND THIS SYSTEM WEAK ENERGY SHOULD FEED INTO THE MEAN TROUGH SUN-MON... PERHAPS FOLLOWED BY FURTHER WEAK ENERGY... WHILE A STRONGER UPR FEATURE ORIGINATING FROM THE BERING SEA/GULF OF ALASKA MAY APPROACH THE PAC NW TOWARD THE END OF THE PERIOD. THERE IS CONSIDERABLE MODEL/ENSEMBLE SPREAD FOR THE STRENGTH/POSN OF THIS LATTER FEATURE. DETAILS ARE BECOMING BETTER REFINED FOR THE EAST COAST TROUGH/CLOSED LOW. HEADING INTO/THROUGH DAY 3 SAT GUIDANCE HAS CONVERGED ON AN OPEN TROUGH SOLN WHICH INITIALLY LEADS TO SOMEWHAT FASTER SYSTEM/FRONTAL PROGRESSION. ALBEIT WITH SOME DIFFS IN EXACT TRACK THE LATEST GFS/ECMWF/CMC RUNS AND THEIR MEANS AGREE WELL IN PRINCIPLE ON THE CLOSING OF AN UPR LOW BY DAY 5 MON WITH A GRADUAL NWD DRIFT TOWARD NEW ENGLAND THEREAFTER. EVOLUTION ALOFT TRANSLATES TO THE SFC AS A LEADING WAVE THAT TRACKS E OF NEW ENGLAND FOLLOWED BY A SRN WAVE THAT WRAPS UP OFF THE MID ATLC COAST AND THEN WEAKENS AS IT HEADS INTO NEW ENGLAND. AT SOME FCST HRS INDIVIDUAL OPERATIONAL MODEL RUNS STRAY A BIT FROM ESTABLISHED CONSENSUS THUS FAVORING A MODEL/ENSEMBLE MEAN BLEND. FROM DAY 3 SAT INTO DAY 5 MON PREFS INCORPORATE VARIOUS ASPECTS OF THE 18Z GFS/GEFS MEAN AND 12Z ECMWF/ECMWF MEAN... WITH ECMWF WEIGHTING SUFFICIENTLY LOW TO DOWNPLAY ITS SLOWER NRN PLAINS TIMING BY MON. BY DAYS 6-7 TUE-WED THE 12Z/18Z GFS RUNS COMPARE WELL ENOUGH TO THE ENSEMBLE MEANS TO ALLOW THEIR PARTIAL INCLUSION FOR DETAIL ENHANCEMENT OF THE MEANS. ...SENSIBLE WEATHER HIGHLIGHTS... MEAN TROUGH ALOFT WILL SUPPORT MULTIPLE DAYS OF PCPN SCATTERED ACROSS PORTIONS OF THE NRN 2/3 OF THE WEST WITH TEMPS BELOW TO WELL BELOW NORMAL. GREATEST COVERAGE OF MINUS 10-15F OR SO ANOMALIES FOR HIGHS SHOULD BE DURING THE WEEKEND. SOME OF THIS COOL AIR WILL SPREAD INTO THE N-CNTRL ROCKIES/NRN HIGH PLAINS BEHIND THE SYSTEM FCST TO TRACK OVER THE NRN PLAINS AROUND MON. THIS SYSTEM MAY ALSO PROVIDE A WELL DEFINED FOCUS FOR ENHANCED RNFL. AREAS OF RAIN/TSTMS OF VARYING INTENSITY SHOULD ALSO EXTEND ACROSS THE REST OF THE PLAINS AND INTO THE MS VLY. SOME CONVECTION MAY BECOME STRONG TO SEVERE. CONSULT SPC OUTLOOKS FOR FURTHER DETAILS ON SEVERE THREATS. ALSO EXPECT NEAR TO ABOVE NORMAL TEMPS TO SPREAD EWD FROM THE PLAINS. THE NRN HIGH PLAINS MAY SEE THE WARMEST TEMPS VS NORMAL ON SAT. LEADING EAST COAST WAVE ON SAT WILL BE ACCOMPANIED BY SOME LOCALLY MDT-HVY RNFL... AND HIGHS UP TO 10-20F BELOW NORMAL IN THE COOL SECTOR. DEVELOPING UPR LOW OVER THE EAST COAST WILL MAINTAIN COOL AND UNSETTLED CONDS INTO EARLY NEXT WEEK. MOST OF THE EAST WILL TREND WARMER WITH TIME AND AREAS TO THE S/SW OF NEW ENGLAND WILL GRADUALLY TREND DRIER. RAUSCH