EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1159 AM EDT SUN MAY 21 2017 VALID 12Z WED MAY 24 2017 - 12Z SUN MAY 28 2017 ...PATTERN OVERVIEW AND MODEL PREFERENCES/UNCERTAINTY... A VIGOROUS UPR TROUGH (WITH EMBEDDED CLOSED LOW) REACHING SWRN CANADA AND NWRN U.S. AS OF THE START OF THE PERIOD EARLY WED SHOULD GRADUALLY BECOME BROADER/MORE DIFFUSE AS IT DRIFTS EWD WHILE THE AXIS OF AN UPSTREAM RIDGE APPROACHES THE WEST COAST. AT THE SAME TIME AN AMPLIFIED UPR TROUGH INITIALLY OVER THE MS VLY WILL LIKELY LIFT AWAY FROM THE ERN STATES BY THE WEEKEND WITH HGTS ALOFT RISING IN ITS WAKE. AS A WHOLE THE MODELS AND ENSEMBLES ARE MODERATELY AGREEABLE WITH THE LARGE SCALE PATTERN WITH PERSISTENT SPREAD REGARDING DETAILS OF ERN U.S. EVOLUTION, THE SRN CANADA/WRN U.S. UPR TROUGH, AND LATE IN THE PERIOD HOW SHRTWV ENERGY FLOWING AROUND THE SRN/SERN PERIPHERY OF THE WRN TROUGH MAY INFLUENCE SFC FEATURES FROM THE PLAINS INTO PARTS OF THE EAST. THROUGH AT LEAST DAY 4 THU AN OPERATIONAL MODEL BLEND INCLUDING THE 06Z GFS AND 00Z ECMWF/UKMET/CMC REFLECTED THE MOST AGREEABLE ASPECTS OF GUIDANCE WHILE DOWNPLAYING LESS CONFIDENT MEDIUM TO SMALLER SCALE DETAILS PRESENT IN EACH THOSE MODEL RUNS. BY DAYS 6-7 SAT-SUN THE OLD 12Z/20 ECMWF RUN COMPARED BETTER TO THE ENSEMBLE MEANS THAN THE CURRENT 00Z RUN WHILE 00Z/06Z GFS BECAME QUESTIONABLY STRONG WITH LOW PRESSURE EMERGING FROM THE PLAINS, SO THAT PART OF THE FCST EMPHASIZED THE 06Z GEFS/00Z ECMWF MEANS ALONG WITH THE 00Z ECMWF MEAN/WPC CONTINUITY. THERE IS STILL A FAIR AMOUNT OF UNCERTAINTY AS TO EXACT DETAILS WITHIN THE OVERALL ERN U.S. UPR TROUGH, WHICH MAKES IT DIFFICULT TO ASSESS THE RELATIVE PROBABILITY THAT DEEPEST SFC LOW PRESSURE WILL TRACK NEAR THE COAST OR FARTHER INLAND. THE INITIAL BLEND WITH ONLY MINOR SUBSEQUENT EDITS MAINTAINED CONTINUITY WITH AN INLAND SCENARIO INTO EARLY FRI BEFORE A COASTAL TRANSITION AS THE SYSTEM BRUSHES THE CANADIAN MARITIMES. BY THE LATTER HALF OF THE PERIOD THE 00Z ECMWF TRENDED FASTER THAN PREVIOUS COUPLE RUNS AND MOST OTHER SOLNS WITH THE DEPARTING UPR TROUGH. ASIDE FROM LOCALIZED DETAILS GUIDANCE APPEARS TO GAINING A BETTER HANDLE ON THE SRN CANADA/WRN U.S. TROUGH AT LEAST FOR THE FIRST HALF OF THE PERIOD. LATER ON THE 06Z GFS BECOMES MORE AMPLIFIED WITH THE DOWNSTREAM RIDGE THAN WHAT MAY BE RECOMMENDED BY THE OVERALL EVOLUTION TOWARD LESS AMPLIFIED MEAN FLOW. TO THE S/SE OF THE UPR TROUGH, EXACTLY HOW DIFFUSE SHRTWV ENERGY EMERGING FROM THE SRN HALF OF THE WRN STATES INTO THE PLAINS, ALONG WITH ASSOC CONVECTION, WILL AFFECT SFC DEVELOPMENT SAT-SUN IS VERY UNCERTAIN. 00Z/06Z GFS RUNS MAY BECOME TOO DEEP WITH THEIR SFC WAVES WHILE THE VERY PROGRESSIVE 00Z ECMWF WAVE WAS A DEPARTURE FROM CONTINUITY AND THE MEANS. HOWEVER NOTE THAT THE FULL ENSEMBLE SPREAD IS QUITE BROAD SO NO INDIVIDUAL SOLN IS AN OUTLIER AT THIS POINT. ...WEATHER HIGHLIGHTS... THE UPR TROUGH/LEADING COLD FRONT PUSHING INTO THE WEST WILL BRING THE REGION A PRONOUNCED COOLING TREND, EVENTUALLY EXTENDING INTO THE NRN-CNTRL HIGH PLAINS, BEFORE THE APPROACHING ERN PAC RIDGE ALOFT SUPPORTS A REBOUND TO ABOVE NORMAL TEMPS OVER THE WEST COAST STATES NEXT WEEKEND. SOME LOCATIONS OVER THE CNTRL-SRN PARTS OF THE WEST MAY STILL SEE UP TO PLUS 10-15F ANOMALIES FOR HIGHS ON WED. WARMEST TEMPS VS NORMAL NEXT WEEKEND SHOULD BE OVER THE NORTHWEST, AGAIN WITH SOME PLUS 10-15F ANOMALIES. AS THE OVERALL SYSTEM PROGRESSES THROUGH THE WEST INTO THE PLAINS/MS VLY EXPECT AREAS OF PRECIP OF VARYING INTENSITY FROM THE NRN-CNTRL ROCKIES EWD/SEWD. SOME ACTIVITY MAY BE LOCALLY HEAVY, AS WELL AS STRONG TO SEVERE FROM THE PLAINS EWD, BUT THERE IS STILL A HIGH LEVEL OF UNCERTAINTY OVER EXACTLY WHERE HIGHEST RNFL TOTALS/STRONGEST CONVECTION MAY OCCUR. HIGHEST ELEVS OF THE NRN ROCKIES MAY SEE SOME SNOW. GRADUALLY CONSOLIDATING SFC LOW PRESSURE AND ASSOC FRONTS WILL LIKELY SUPPORT AREAS OF RAIN AND SHWRS/TSTMS ACROSS THE ERN U.S. WED-THU, PSBLY LINGERING OVER THE NORTHEAST INTO FRI. THE BEST PROBABILITY FOR HEAVIEST RAIN SHOULD BE OVER THE FLORIDA PENINSULA AS THE COLD FRONT APPROACHES FROM THE SERN U.S./GULF OF MEXICO AS WELL AS FROM THE OH VLY/CNTRL APLCHNS INTO THE NORTHEAST NEAR THE SFC LOW. THIS MORNING'S SPC OUTLOOK INDICATES SOME SEVERE POTENTIAL OVER FLORIDA EARLY IN THE PERIOD. THIS SYSTEM WILL BRING COOL DAYTIME TEMPS FROM THE PLAINS/MS VLY INTO THE EAST FOLLOWED BY A WARMING TREND TO NEAR/ABOVE NORMAL READINGS FOR THE WEEKEND. RAUSCH