EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1158 AM EDT THU MAY 01 2014 VALID 12Z SUN MAY 04 2014 - 12Z THU MAY 08 2014 ...OVERVIEW AND PREFERENCES... GUIDANCE HAS STABILIZED WITH THE FCST FOR SIGNIFICANT AMPLIFICATION OF AN ERN PAC TROUGH AS IT MOVES INTO THE WEST... WITH LEADING HGT FALLS REACHING THE PLAINS BY THE MIDDLE OF NEXT WEEK. DOWNSTREAM EXPECT A RIDGE TO BUILD INTO THE E-CNTRL/SERN STATES WHILE INITIAL NERN CONUS TROUGHING DRIFTS INTO THE WRN ATLC. THIS EVOLUTION SHOULD GENERALLY BRING THE MOST ACTIVE WEATHER TO AREAS FROM THE PAC NW EWD INTO THE GRTLKS. FOR DAYS 3-4 SUN-MON GUIDANCE DIFFS ARE SUFFICIENTLY SMALL TO FAVOR A CONSENSUS APPROACH WEIGHTED MORE TOWARD THE 00Z-06Z GFS/00Z ECMWF VERSUS THE 06Z GEFS/00Z ECMWF MEANS. AFTER MON CONFIDENCE IN VARIOUS OPERATIONAL DETAILS DECREASES SO THE DAYS 5-7 TUE-THU FCST STARTS WITH A BLEND OF HALF 00Z ECMWF MEAN AND THE REMAINDER 06Z GEFS/00Z NAEFS MEANS. ...GUIDANCE EVALUATION... DURING THE EARLY PART OF THE FCST WHEN A MODEL/ENSEMBLE CONSENSUS IS REASONABLE... PRIMARY DETAIL ISSUES INVOLVE THE EVOLUTION OF FAIRLY VIGOROUS MID LVL ENERGY CROSSING THE NORTHEAST AROUND SUN-SUN NIGHT/ASSOC SFC LOW PRESSURE ALONG WITH AMPLITUDE OF THE TROUGH REACHING THE WEST COAST. IN BOTH CASES MOST SOLNS ARE WITHIN THE TYPICAL RANGE OF ERROR FOR DAYS 3-4 FCSTS. CONSULT THE MODEL DIAGNOSTIC DISCUSSION PMDHMD FOR UPDATED PREFS BASED ON NEW 12Z GUIDANCE AS THE SPREAD FOR THE NERN SYSTEM IN PARTICULAR DEVELOPS OVER SRN CANADA AROUND DAY 2 SAT. BY THE LATTER HALF OF THE PERIOD THE GREATEST QUESTION MARK WILL BE WHAT HAPPENS TO THE ENERGY WITHIN THE CORE OF THE AMPLIFYING WRN TROUGH. THIS WILL DETERMINE THE STRENGTH/TRACK/TIMING OF SFC LOW PRES FOR WHICH THERE HAS BEEN QUITE GOOD CLUSTERING OVER THE CNTRL PLAINS AS OF 12Z WED BUT RAPIDLY EXPANDING SPREAD THEREAFTER. JUST THE 00Z AND 06Z RUNS OF THE GFS OFFER A GOOD CONTRAST IN POTENTIAL EVOLUTIONS WITH THE 00Z MORE SHEARED/ELONGATED ALOFT LEADING TO WEAKER SFC LOW PRESSURE WHILE THE 06Z GFS... AND 00Z CMC... BECOME MORE CONSOLIDATED/NEG TILT ALOFT BY THU TO GENERATE DEEPER LOW PRESSURE. AT THIS TIME THE ENSEMBLE GUIDANCE LEANS MORE TOWARD A MORE SUBDUED FORM OF THE 00Z GFS/ECMWF WITH AN EJECTING IMPULSE SUPPORTING SFC WAVINESS REACHING THE UPR MS VLY REGION BY EARLY THU VERSUS A MORE CONSOLIDATED SYSTEM. ALSO BIASES AND MAJORITY OF GUIDANCE SUGGEST THE 06Z GFS IS OVERDONE WITH SEWD EXTENT OF THE TROUGH ALOFT BY NEXT WED-THU. AS FOR OTHER QUESTIONABLE MODEL DETAILS OF NOTE... THE 00Z ECMWF PUTS MORE OF A DENT IN THE UPSTREAM ERN PAC RIDGE ALOFT NEXT WED/THU... PULLS THE SWRN CANADA UPR LOW W/SW OF CONSENSUS BY TUE... AND BECOMES MORE AMPLIFIED WITH THE NERN CONUS/WRN ATLC TROUGH ALOFT. THE 00Z GFS JOINS THE 00Z ECMWF IN BEING MORE AMPLIFIED WITH THE BAJA CALIF PART OF THE WRN TROUGH RELATIVE TO THE MAJORITY OF SOLNS. ...SENSIBLE WEATHER HIGHLIGHTS... THE AMPLIFYING UPR TROUGH MOVING INTO THE WEST WILL BE RESPONSIBLE FOR SPREADING MSTR FROM THE PAC NW/CNTRL INTERIOR WEST ACROSS THE NRN TIER OF THE CONUS. HIGHEST PCPN TOTALS ARE MOST LIKELY OVER FAVORED TERRAIN IN THE NW... OVER THE NRN HIGH PLAINS/ERN SLOPES OF THE NRN ROCKIES WHERE LOW LVL UPSLOPE FLOW MAY ENHANCE ACTIVITY... AND THE UPR MS VLY/GRTLKS REGION WHERE WARM ADVECTION AHEAD OF PLAINS LOW PRESSURE MAY SUPPORT LOCALLY HVY RNFL. SNOW OVER THE WEST SHOULD BE CONFINED TO HIGH ELEVS THOUGH SNOW LVLS SHOULD DECLINE SOMEWHAT AS THE UPR TROUGH MOVES INTO THE WEST. SOME CONVECTION MAY DEVELOP OVER THE CNTRL-SRN PLAINS/MID MS VLY BY DAY 7 THU. FARTHER EWD... FAIRLY VIGOROUS SFC LOW CROSSING NEW ENGLAND SUN-SUN NIGHT SHOULD BE ACCOMPANIED BY MOSTLY RNFL OF VARYING INTENSITY. THE TRAILING FRONT SHOULD STALL ALONG A SRN MID ATLC TO CNTRL PLAINS ORIENTATION AND MAY SERVE AS A FOCUS FOR ONE OR MORE AREAS OF RNFL NEXT WEEK. WARM SECTOR TEMPS MAY REACH 15-20F ABOVE NORMAL AT SOME LOCATIONS IN THE CNTRL PLAINS/SRN HIGH PLAINS SUN-TUE... PSBLY APPROACHING DAILY RECORD VALUES FOR DAYTIME HIGHS. CNTRL-SRN PARTS OF THE WEST WILL SEE A PRONOUNCED COOLING TREND AFTER SUN WHILE SOME OF THE PLAINS WARMTH SHOULD GRADUALLY EXPAND INTO PORTIONS OF THE EAST. MEANWHILE NRN TIER AREAS SHOULD SEE BELOW NORMAL HIGHS MOST DAYS. RAUSCH