EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1158 AM EDT THU MAY 14 2015 VALID 12Z SUN MAY 17 2015 - 12Z THU MAY 21 2015 ...PATTERN OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES... EXPECT LITTLE CHANGE IN THE ERN PAC/WRN NOAM PATTERN WITH A MEAN TROUGH AXIS NEAR THE WEST COAST OF THE U.S. AND STRONG RIDGE COVERING WRN CANADA. INDIVIDUAL ERN PAC TROUGHS/EMBEDDED LOWS WILL FEED INTO AND EJECT FROM THE WEST COAST TROUGH. DOWNSTREAM FLOW WILL SEE MORE OF A CHANGE AS AN INITIAL RIDGE STEADILY FLATTENS. DURING DAYS 3-5 SUN-TUE THERE IS SOME LINGERING DETAIL SPREAD FOR SOME ASPECTS OF THE FCST BUT OVERALL A BLEND EMPHASIZING THE 00Z ECMWF AND 00Z/06Z GFS PROVIDES A GOOD CONSENSUS SOLN WITH REASONABLE DETAIL. GUIDANCE IS BETTER CLUSTERED THAN IN PREVIOUS DAYS FOR THE SYSTEM TRACKING NEWD FROM THE NRN PLAINS. FARTHER EWD... TRENDS FROM THE PAST DAY APPEAR TO BE HEADING TO A COMPROMISE ABOUT 2/3 TOWARD EARLIER ECMWF/UKMET GUIDANCE THAT HAD BEEN MORE AMPLIFIED WITH THE SHRTWV CROSSING NEW ENGLAND ON SUN AND FARTHER SWD WITH THE E COAST SFC FRONT. SOME SPREAD STILL EXISTS FOR THIS SFC FRONT BUT SOLNS ARE CLOSER THAN 24 HRS AGO. THE IDEA OF A WELL DEFINED WAVE TRACKING OFF THE MID ATLC COAST ON TUE IS A MORE RECENT DEVELOPMENT IN THE MODELS. MEANWHILE DIFFS ARE MODEST WITH THE NEXT ERN PAC UPR LOW COMING INTO THE WEST. MODEL DETAILS DIVERGE A LITTLE MORE AFTER TUE SO DAY 6 WED INCORPORATES MORE ENSEMBLE MEAN GUIDANCE AS A TRANSITION TO A DAY 7 THU BLEND THAT CONSISTS OF 50/30/20 WEIGHTING OF THE 00Z ECMWF MEAN/00Z NAEFS MEAN/06Z GEFS MEAN. THE UPR SYSTEM REACHING THE WEST BY TUE SHOULD CONTINUE INTO THE N-CNTRL ROCKIES BEFORE SHEARING OUT AS IT ENTERS CONFLUENT FLOW ALOFT. THERE IS STILL ENOUGH UNCERTAINTY WITH DETAILS OF NRN STREAM FLOW TO LEAVE SOME DOUBT REGARDING THE SHEARING PROCESS ALOFT AS WELL AS ANY ASSOC SFC REFLECTION WHICH SHOULD BE ON THE WEAK SIDE. THE ENSMEAN COMPROMISE ACCOUNTS FOR DIFFS IN SFC PATTERN OVER THE PLAINS LATE IN THE PERIOD. AT THE SAME TIME THE NEXT BUNDLE OF ENERGY SHOULD APPROACH THE WEST COAST BY NEXT WED-THU. ENSEMBLE MEANS SHOW FAIRLY GOOD AGREEMENT AND CONTINUITY... WITH ECMWF MEANS TENDING TO BE SOMEWHAT DEEPER THAN GEFS MEANS BY THU. FLATTENING ERN CONUS FLOW ALOFT SHOULD HELP TO PUSH THE FRONT NEARING THE EAST COAST TUE ONWARD INTO THE ATLC. ...SENSIBLE WEATHER HIGHLIGHTS... GULF INFLOW AHEAD OF THE COLD FRONT PROGRESSING EWD FROM THE PLAINS SHOULD ENHANCE RNFL TOTALS AT SOME LOCATIONS WITH AN AREA FROM CNTRL/E-CNTRL TX NEWD INTO AR SHOWING THE BEST POTENTIAL FOR HEAVIEST AMTS SUN-MON. SOME LOCALLY HVY ACTIVITY IS ALSO PSBL FARTHER NEWD INTO THE CNTRL APLCHNS AND VICINITY. CONSULT LATEST SPC OUTLOOKS FOR LATEST DETAILS ON SEVERE WEATHER THREATS WHICH SHOULD FOCUS ON THE MID-UPR MS VLY EARLY IN THE PERIOD. ANCHORING LOW PRES SHOULD CONCENTRATE A NARROW BAND OF ENHANCED PCPN OVER THE NRN TIER ON SUN. NEXT SYSTEM MOVING INTO THE WEST AND THEN EJECTING INTO THE PLAINS WILL SUPPORT ANOTHER AREA OF MEANINGFUL PCPN ACROSS THE CNTRL/N-CNTRL WRN STATES AND THEN AN EPISODE OF LOCALLY HVY RNFL FROM THE ERN SLOPES OF THE ROCKIES... WHERE LOW LVL UPSLOPE FLOW MAY AID DEVELOPMENT... INTO THE PLAINS. SOME SNOW IS PSBL IN THE HIGHEST TERRAIN. EXCEPT FOR THE NRN INTERIOR WEST EXPECT BELOW NORMAL TEMPS FROM THE WRN STATES THROUGH THE PLAINS INTO GRTLKS WITH GREATEST NEG ANOMALIES LIKELY FROM THE ERN SLOPES OF THE ROCKIES INTO THE NRN PLAINS. MIN TEMPS IN PARTICULAR WILL BE WARM AHEAD OF THE COLD FRONT NEARING THE EAST COAST BY TUE. RAUSCH