EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 244 AM EDT FRI MAR 20 2015 VALID 12Z MON MAR 23 2015 - 12Z FRI MAR 27 2015 ...OVERVIEW... OVER THE COURSE OF THE FCST PERIOD THERE IS REASONABLE AGREEMENT FROM LATEST GUIDANCE THAT THE MEAN FLOW SHOULD TREND FROM BEING PROGRESSIVE WITH LOW AMPLITUDE TOWARD A SLOWER MOVING AND HIGHER AMPLITUDE PATTERN FEATURING THE FAMILIAR WEST COAST RIDGE/ERN NOAM TROUGH. THE MOST NOTABLE UNCERTAINTIES WILL BE WITH ONGOING DETAIL DIFFS/TIMING TRENDS DURING THE FIRST HALF OF NEXT WEEK AND THEN THE DISTRIBUTION OF ENERGY WITHIN THE CONUS MEAN TROUGH BY THE LATTER HALF OF THE WEEK. ...GUIDANCE EVALUATION AND PREFERENCES... THE PROMINENT SYSTEM OF INTEREST DURING THE PERIOD WILL BE SUPPORTED BY SHRTWV ENERGY ENTERING THE WEST ON MON. SFC LOW PRES SHOULD TRACK FROM THE NORTHWEST INTO THE NRN PLAINS EARLY IN THE WEEK... TO THE GRTLKS BY WED... AND CONTINUE NEWD THEREAFTER. A TRAILING WAVY COLD FRONT WILL CROSS MOST OF THE CONUS... REACHING THE EAST COAST LATE IN THE WEEK. OVERALL TRENDS IN GUIDANCE OVER THE PAST 1-2 DAYS HAVE BEEN TOWARD FASTER PROGRESSION OF THE SYSTEM WITH THE BEST CONSENSUS FROM THE 12Z/18Z CYCLE REFLECTING THIS TREND AS WELL. IN SPITE OF THIS TREND THERE WAS NOT ENOUGH OTHER SUPPORT TO ACCELERATE THE SYSTEM OR CLOSE OFF NRN TIER ENERGY ALOFT TO THE EXTENT OF THE 12Z/18Z GFS RUNS. THEREFORE PREFERRED TO PLACE GREATEST EMPHASIS ON THE 12Z ECMWF MEAN/ECMWF. HOWEVER THE NEW 00Z GUIDANCE THUS FAR COULD OFFER MORE POTENTIAL FOR A GFS TYPE EVOLUTION. STARTING AROUND WED AND CONTINUING INTO LATE WEEK THE MODELS AND ENSEMBLES DIVERGE SOMEWHAT WITH RESPECT TO HOW MUCH SEPARATION OCCURS IN THE SWRN PART OF THE OVERALL UPR TROUGH AS WELL AS WITH NRN STREAM DETAILS. THESE TWO UNCERTAINTIES PLAY AN INCREASINGLY IMPORTANT ROLE IN DETERMINING SFC FRONT PROGRESSION OVER THE ERN HALF OF THE CONUS. THUS FAR SOME OPERATIONAL MODEL RUNS HAVE BEEN MORE SUGGESTIVE OF ENERGY SEPARATING SOMEWHERE OVER THE WRN CONUS/NRN MEXICO VERSUS THE ENSEMBLE MEANS... THOUGH SOME INDIVIDUAL ENSEMBLE MEMBERS DO SHOW A SEPARATED SCENARIO. TELECONNECTIONS RELATIVE TO THE CORE OF POSITIVE HGT ANOMALIES OVER OR JUST E OF VANCOUVER ISLAND BY THE D+8 TIME FRAME SHOW THE BEST SUPPORT FOR THE ENSEMBLE MEANS AND NON-GFS RUNS THAT SHOW JUST A HINT OF SWRN CONUS ENERGY WHILE MOST OF THE UPR TROUGHING REACHES THE E-CNTRL STATES BY FRI. THE 00Z GFS CONTINUES TO HOLD MORE ENERGY SWWD THAN RECOMMENDED BY TELECONS AND MOST ENSMEANS. BEHIND THIS SYSTEM THE 12Z ECMWF BECOMES FASTER THAN MOST OTHER SOLNS WITH ERN PAC SHRTWV ENERGY BY DAY 7 FRI... FAVORING EXCLUSION FROM THE FAVORED BLEND AFTER DAY 6 THU. ON THE OTHER SIDE OF THE COUNTRY THERE IS REASONABLE CONSENSUS MINUS CMC RUNS THAT WAVINESS OVER THE GULF COAST/FL-GA BORDER AS OF EARLY MON SHOULD BE QUITE FLAT AS IT PROGRESSES INTO THE ATLC. BASED ON ABOVE CONSIDERATIONS THE FAVORED BLEND BASED ON GUIDANCE THROUGH THE 18Z CYCLE CONSISTS OF THE 12Z ECMWF MEAN/12Z ECMWF/12Z NAEFS MEAN/18Z GEFS MEAN IN ORDER FROM HIGHEST TO LOWEST WEIGHTING THROUGH DAY 6 THU WITH THE 12Z ECMWF EXCLUDED ON FRI. ...SENSIBLE WEATHER HIGHLIGHTS... SYSTEM CROSSING THE CONUS DURING THE PERIOD WILL BRING RNFL AND HIGHER ELEV SNOW TO THE NRN HALF OF THE WEST EARLY IN THE WEEK... THEN PORTIONS OF THE CNTRL-ERN CONUS THEREAFTER. SNOW TO THE E OF THE ROCKIES SHOULD BE CONFINED TO EXTREME NRN AREAS. SOME LOCALLY ENHANCED PCPN IS PSBL DEPENDING ON EXACT EVOLUTION OF DYNAMICS ALOFT OVER THE NRN TIER AND SHRTWV IMPULSES/FRONTAL WAVES FARTHER S IN THE WARM SECTOR. EARLY IN THE WEEK EXPECT HIGH PRESSURE TO SUPPORT WELL BELOW NORMAL TEMPS OVER THE NORTHEAST WHILE THE PLAINS WILL BE RATHER WARM AHEAD OF APPROACHING LOW PRESSURE. PROGRESSION OF THIS SFC LOW AND TRAILING FRONT WILL BRING A BRIEF WARMUP TO THE EAST BEFORE A COOLER TREND BECOMES ESTABLISHED ONCE AGAIN LATE IN THE WEEK. AT THE SAME TIME THE UPR RIDGE FCST TO BUILD NEAR THE WEST COAST SHOULD SUPPORT A BROAD AREA OF PLUS 10-20F ANOMALIES FOR HIGHS OVER THE WRN STATES BY NEXT FRI. RAUSCH