EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1159 AM EDT THU AUG 07 2014 VALID 12Z SUN AUG 10 2014 - 12Z THU AUG 14 2014 ...OVERVIEW AND PREFERENCES... EXPECT A FAIRLY STABLE LARGE SCALE PATTERN WITH TROUGHING TO THE SW OF THE ALASKA MAINLAND AND RIDGING TO THE NW OF ALASKA TELECONNECTING TO THE CONSENSUS FCST OF A MEAN RIDGE OVER INTERIOR WRN NOAM AND TROUGHING OVER ERN NOAM. SIGNIFICANT DETAIL UNCERTAINTIES REMAIN THOUGH... ESPECIALLY ALOFT NEAR THE WEST COAST AND SFC/ALOFT NEAR THE EAST COAST. OVERALL AN AVG OF LATEST MODEL/ENSEMBLE MEAN SOLNS PROVIDES A REASONABLE STARTING POINT TO REFLECT THE MOST COMMON IDEAS OF GUIDANCE FOR DAYS 3-5 SUN-TUE. DECREASING CONFIDENCE IN OPERATIONAL MODEL DETAILS LEADS TO FAVORING THE 00Z ECMWF MEAN AND 06Z GEFS/00Z NAEFS MEANS BY NEXT WED-THU. ...GUIDANCE EVALUATION... LATEST SOLNS HAVE CONVERGED FAIRLY WELL FOR THE UPR LOW FCST NEAR THE CA COAST AS OF DAY 3 SUN... WITH DECENT AGREEMENT CONTINUING INTO DAY 5 TUE AS THE FEATURE BEGINS TO EJECT INLAND. HOWEVER MODEL/ENSEMBLE CONTINUITY AND SPREAD REMAIN POOR WITH THE DETAILS OF TROUGH ENERGY EXPECTED TO APPROACH THE PAC NW/BC BY TUE AND OVERALL SHAPE OF ERN PAC/WRN NOAM FLOW DURING THE LATTER HALF OF THE PERIOD. WITH THIS UPSTREAM ENERGY THE 00Z ECMWF/UKMET/CMC IN VARYING WAYS PULL OFF A COMPACT UPR LOW TO REINFORCE THE MEAN WEAKNESS NEAR THE WEST COAST. BY DAY 7 THU THIS SCENARIO CONTRASTS TO THE 12Z ECMWF THAT HAD RIDGE WHERE AN UPR LOW IS NOW FCST. LATEST GFS RUNS SHOW MORE OF THIS ENERGY CONTINUING INTO SRN CANADA. THE FULL ENSEMBLE SPREAD REMAINS BROAD ENOUGH NOT TO PRECLUDE ANY SPECIFIC SOLN YET. ONE NOTICEABLE TREND IN THE ENSEMBLES IS SOME GRAVITATION TOWARD PAC NW/BC RIDGING BY THE END OF THE PERIOD. TELECONNECTIONS RELATIVE TO THE NEG/POS HGT ANOMALY CENTERS TO THE SW/NW OF ALASKA RESPECTIVELY SUGGEST ONLY A MODEST WEAKNESS ALONG OR JUST OFFSHORE THE WEST COAST... WHICH IS BEST REFLECTED BY THE ENSEMBLE MEANS BY DAYS 6-7 WED-THU. THE MEANS ALSO AGREE WELL WITH THE SRN CANADA/NRN TIER SHRTWV BRINGING A FRONT INTO THE NRN PLAINS BY NEXT THU. FARTHER EWD THE MOST MEANINGFUL DIFFS ARE OVER THE OH VLY/GRTLKS AND ALONG THE EAST COAST. EARLY-MID PERIOD THE PAST COUPLE DAYS OF GFS RUNS HAVE BEEN ON THE STRONGER SIDE OF GUIDANCE WITH THE OH VLY/GRTLKS SFC REFLECTION DUE TO STRONGER DYNAMICS ALOFT. AT SOME FCST HRS QUESTIONABLY CONCENTRATED QPF/PSBL FEEDBACK MAY BE ADVERSELY IMPACTING THE GFS EVOLUTION. MEANWHILE DURING MOST OF THE PERIOD THERE IS STILL FAIRLY WIDE ENSEMBLE SPREAD FOR SFC LOW PRES EXPECTED TO TRACK ALONG OR JUST OFFSHORE THE EAST COAST. AMONG OPERATIONAL MDLS THE 00Z ECMWF HAS ONE OF THE MORE OFFSHORE SOLNS FOR ITS BEST DEFINED WAVE AFTER MON... LEADING TO A TRACK ON THE SRN/SERN EDGE OF MOST THOUGH NOT ALL ENSEMBLE MEMBERS. IN SPITE OF THESE SEPARATE ISSUES LEADING INTO DAY 7 THU THERE IS FAIR CONFIDENCE THAT SFC LOW PRES SHOULD CONSOLIDATE IN THE VICINITY OF NEW ENGLAND AND/OR CANADIAN MARITIMES BY THE END OF THE PERIOD AS THE MID LVL TROUGH APPROACHES. THE DAY 7 SFC LOW WAS DEEPENED SLIGHTLY FROM THE INITIAL ENSEMBLE MEAN BLEND BASED DECENT CLUSTERING OF THE MID LVL SYSTEM. ...SENSIBLE WEATHER HIGHLIGHTS... EXPECT ONE OR MORE PERIODS OF CONVECTION FROM THE INTERIOR WEST THROUGH THE ROCKIES WITH THE BEST ORGANIZED ACTIVITY LIKELY ASSOC WITH THE UPR LOW THAT EJECTS FROM THE CA COAST DURING THE FIRST HALF OF NEXT WEEK AND DIURNAL CONVECTION OVER THE FOUR CORNERS REGION. CONFIDENCE IN CONVECTIVE DETAILS DURING THE LATTER HALF OF THE PERIOD DECREASES IN LINE WITH THE DIVERGENCE OF MODEL/ENSEMBLE SOLNS FOR FLOW ALOFT. GREATEST TEMP ANOMALIES SHOULD BE OVER THE NORTHWEST WITH SOME MAX READINGS EXCEEDING 10F ABOVE NORMAL SUN-MON. EXPECT A MODEST COOLING TREND TUE-WED BUT RISING HGTS ALOFT MAY SUPPORT WARMER TEMPS AGAIN THU. AN AREA FROM THE CNTRL PLAINS THROUGH THE SOUTHEAST AND PSBLY SRN MID ATLC SHOULD SEE THE BEST POTENTIAL FOR LOCALLY HVY RNFL DURING THE PERIOD... WITH A SLOW MOVING WAVY FRONT IN THE VICINITY SUN-TUE AND AN UPSTREAM FRONT DROPPING SEWD FROM THE NRN PLAINS LIKELY REPLACING THE INITIAL BNDRY OVER THE SOUTH BY NEXT WED-THU. CONFIDENCE IS LOWER IN DETAILS FARTHER NWD GIVEN THE SPREAD IN SFC SOLNS FROM THE OH VLY/GRTLKS THROUGH THE WRN ATLC... THOUGH CONSENSUS EVOLUTION SFC/ALOFT SHOULD AT LEAST SUPPORT A PERIOD OF UNSETTLED WEATHER OVER THIS REGION. THE AFOREMENTIONED UPSTREAM COLD FRONT SHOULD BE ACCOMPANIED BY SOME AREAS OF CONVECTION. YET ANOTHER FRONT REACHING THE NRN TIER AT THE END OF THE PERIOD MAY SUPPORT SHWRS/TSTMS. THE OVERALL PATTERN IS EXPECTED TO SUPPORT NEAR TO BELOW NORMAL TEMPS OVER MUCH OF THE NRN 2/3 OF THE CONUS E OF THE ROCKIES WITH NEAR TO ABOVE NORMAL READINGS CONFINED TO SRN AREAS. RAUSCH