EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 241 AM EDT SAT APR 09 2016 VALID 12Z TUE APR 12 2016 - 12Z SAT APR 16 2016 ...OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT... GUIDANCE MAINTAINS THE THEME OF BETTER THAN AVG AGREEMENT WITH THE LARGE SCALE PATTERN FCST BUT VARIOUS UNCERTAINTIES FOR SOME LOCALLY/REGIONALLY IMPORTANT DETAILS. THE FCST IS ON TRACK FOR AMPLIFICATION OF NERN PAC TROUGHING INTO THE WEST WHILE THE DOWNSTREAM RIDGE PROGRESSES ACROSS THE ROCKIES/PLAINS AND INTO THE MS VLY. AT THE SAME TIME AN ERN NOAM MEAN TROUGH... CONSISTING OF A COMBINATION OF NRN STREAM FLOW AND BY THE LATTER HALF OF THE PERIOD PSBLY SRN STREAM ENERGY... SHOULD REACH THE EAST COAST/EXTREME WRN ATLC BY FRI-SAT. BASED ON COMPARISON OF 12Z/18Z MODEL-ENSEMBLE SOLNS THE UPDATED FCST INCORPORATED IDEAS FROM THE 12Z ECMWF/UKMET/CMC AND NAEFS/ECMWF MEANS DAY 3 TUE INTO DAY 5 THU AND THEN A 50/30/20 WEIGHTING OF THE 12Z ECMWF MEAN/NAEFS MEAN/GEFS MEAN DAYS 6-7 FRI-SAT. GFS/GEFS MEAN RUNS LEANED ON THE FAST SIDE WITH ERN CANADA LOW PRES/NRN PART OF THE TRAILING COLD FRONT AS OF EARLY TUE WHILE DIFFS ORIGINATING OVER THE NRN PAC/ALEUTIANS ULTIMATELY LED TO POOR GFS COMPARISON TO OTHER SOLNS FROM THE ERN PAC INTO THE LOWER 48. FAST PROGRESSION OF NRN PAC ENERGY IN THE 12Z/18Z GFS AS EARLY AS THE SHORT RANGE PERIOD LED TO A DEEP UPR LOW STRAYING TO THE FAST/NRN SIDE OF THE SPREAD OVER THE ALEUTIANS/BERING SEA BY MIDWEEK. AS A CONSEQUENCE THE GFS WAS MORE AGGRESSIVE TO AMPLIFY THE UPR TROUGH HEADING INTO THE WEST AND STRAYED TO THE FAST SIDE WITH THE UPR SYSTEM INITIALLY OVER THE SWRN CONUS/NWRN MEXICO. GEFS MEANS WERE NOT AS EXTREME WITH VARIOUS DIFFS AS THE OPERATIONAL RUNS. THE NEW 00Z GFS HAS MADE A CONSIDERABLE ADJUSTMENT TOWARD CONSENSUS ACROSS THE ALEUTIANS. AS THE UPR TROUGH MOVES INTO THE WEST THERE IS STILL A FAIR AMOUNT OF MODEL/ENSEMBLE SPREAD REGARDING THE ULTIMATE TRACK OF A PSBL EMBEDDED LOW. THE MOST LIKELY TRACK APPEARS TO BE OVER OR NEAR THE GRTBASIN. GFS/CMC RUNS HAVE TENDED TO OFFER THE MOST SRN UPR LOW TRACK. LATER IN THE PERIOD THE ENSEMBLE MEAN BLEND RESOLVES TIMING DIFFS BTWN THE FASTER ECMWF MEAN AND SLOWER NAEFS/GEFS. THE 12Z ECMWF ACTUALLY STRAYS A LITTLE FASTER THAN ITS MEAN WITH LEADING HGT FALLS OVER THE ROCKIES/PLAINS BY LATE IN THE WEEK. GUIDANCE CONTINUES TO SHOW VARIABILITY WITH EXACT DETAILS OF SRN STREAM ENERGY TRACKING OUT OF THE SOUTHWEST. SLOWER TREND OF THE 00Z GFS IS MORE SIMILAR TO CONSENSUS THAN THE FAST 18Z RUN BUT IT STILL BECOMES MORE DIFFUSE WITH THE SHRTWV THAN MOST OTHER SOLNS BY 12Z WED. CONFIDENCE REMAINS LACKING FOR THE ULTIMATE EVOLUTION/TIMING OF THIS SRN STREAM ENERGY ALONG WITH NRN STREAM FLOW COMPRISING THE REMAINDER OF THE OVERALL ERN MEAN TROUGH. OVER THE PAST 1-2 DAYS THERE HAS BEEN A NOTICEABLE SUPPRESSION OF POTENTIAL ASSOC SFC WAVINESS ALONG OR OFFSHORE THE GULF/EAST COASTS. CONTINUED WIDE SPREAD AND SIGNIFICANT DETAIL DIFFS BTWN CONSECUTIVE RUNS MAKE IT DIFFICULT TO INCORPORATE ANY SPECIFIC OPERATIONAL MODEL SCENARIO AT THIS TIME. IN CONTRAST THERE IS GOOD CLUSTERING FOR THE SFC HIGH TRACKING FROM THE UPR MS VLY THROUGH THE GRTLKS INTO ERN CANADA ALONG WITH THE RIDGE FCST TO COVER MUCH OF THE ERN HALF OF THE LOWER 48. ...SENSIBLE WEATHER HIGHLIGHTS/THREATS... WEATHER WILL BECOME INCREASINGLY ACTIVE/UNSETTLED ACROSS THE WEST AND EVENTUALLY INTO THE PLAINS AS UPR TROUGHING AMPLIFIES INTO AND MOVES ACROSS THE WEST. LOCALLY ENHANCED RAIN/HIGH ELEV SNOW WILL BE PSBL ESPECIALLY OVER THE NRN 2/3 OF THE WEST... WITH DETAILS ABLE TO BE REFINED ONCE THERE IS BETTER AGREEMENT ON THE EXISTENCE/TRACK OF AN EMBEDDED UPR LOW. BY LATE IN THE WEEK THE GRADUAL ADVANCE OF THE UPR TROUGH SHOULD LEAD TO INCREASING COVERAGE/INTENSITY OF PLAINS RNFL WHILE ACTIVITY TAPERS OFF FROM THE WEST COAST INLAND. THIS SYSTEM WILL BRING A COUPLE DAYS OF COOL TEMPS TO THE WEST WHILE PROMOTING SOME VERY WARM TEMPS OVER THE PLAINS... ESPECIALLY THE NRN TIER WHERE ONE OR MORE DAYS OF PLUS 10-20F ANOMALIES ARE PSBL. WAVY FRONT NEAR THE EAST/GULF COASTS AS OF TUE WILL BE ACCOMPANIED BY RNFL OF VARYING INTENSITY... SOME LOCALLY MDT-HVY. SRN STREAM ENERGY EJECTING FROM THE SOUTHWEST MAY HELP TO GENERATE ANOTHER AREA OF HEAVIER RNFL FROM PARTS OF TX EWD ALONG THE GULF COAST. THE PERIOD WILL START OFF VERY CHILLY OVER THE EAST WITH GREATEST ANOMALIES OF MINUS 10-20F FOR HIGHS OVER THE MIDWEST/GRTLKS ON TUE. COOL TEMPS OVER THE EAST WILL PERSIST THE LONGEST NEAR THE EAST COAST WHILE PLAINS WARMTH GRADUALLY SPREADS ACROSS AND BEYOND THE MS VLY. RAUSCH