EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 246 AM EDT SUN AUG 09 2015 VALID 12Z WED AUG 12 2015 - 12Z SUN AUG 16 2015 ...OVERVIEW AND PREFERENCES...... EXPECT SOME MODERATION OF THE AMPLIFIED TROUGH/RIDGE/TROUGH PATTERN WITH TIME... AS AN UNSEASONABLY DEEP UPR LOW OFF THE WEST COAST EJECTS NEWD AND HGTS RISE WITHIN THE CENTRAL PART OF THE ERN TROUGH ALBEIT WITH SOME RELOADING TO THE N. A STRONG UPR HIGH OVER THE SRN ROCKIES WILL LIKELY MOVE VERY LITTLE DURING THE PERIOD. AS FOR DEPICTING THE FCST DETAILS... ESPECIALLY IN THE FIRST HALF OF THE PERIOD MODELS/ENSEMBLES ARE SHOWING A GRADUAL IMPROVEMENT IN CLUSTERING THOUGH WITH ONGOING TRENDS IN SOME CASES. OVERALL A CONSENSUS BLEND WEIGHTED MORE TO THE 12Z ECMWF/18Z GFS RELATIVE TO THEIR ENSEMBLE MEANS REFLECTS THE MOST COMMON IDEAS OF GUIDANCE INTO DAY 5 FRI. PROPAGATION OF INCREASING SPREAD FOR DETAILS OF NRN PAC FLOW INTO SRN CANADA AND EXTREME NRN LOWER 48 DECREASES CONFIDENCE IN ANY PARTICULAR OPERATIONAL SOLN BY DAYS 6-7 SAT-SUN... THUS FAVORING THE 18Z GEFS/12Z ECMWF MEANS FOR THAT PART OF THE FCST. ...GUIDANCE EVALUATION... DURING MID-LATE WEEK GUIDANCE IS SETTLING TOWARD A COMMON SOLN FOR THE DEEP UPR LOW FCST TO BE OFF THE NRN CA COAST AS OF EARLY WED. THIS POSN IS CONSISTENT WITH THE MAJORITY CLUSTERING FROM 24 HRS AGO. NOTE THAT SOME HGTS NEAR THE UPR LOW MAY BE 3-4 STDEVS BELOW NORMAL NEAR THE START OF THE PERIOD. BY FRI THERE IS AGREEMENT IN PRINCIPLE THAT THE UPR LOW SHOULD BE IN THE PROCESS OF EJECTING NEWD AS NERN PAC SHRTWV ENERGY APPROACHES/REACHES BC. IT IS AROUND THAT TIME WHEN TIMING DIFFS BECOME NOTICEABLE WITH NO CLEAR DOMINANT CLUSTER AT THE MOMENT... AND ALSO WHEN IT BECOMES UNCLEAR EXACTLY HOW THE TWO FEATURES WILL INTERACT. EVEN WITH SPREAD DEVELOPING ALOFT THERE IS A DECENT SIGNAL TOWARD WELL DEFINED LOW PRES OVER ALBERTA AROUND FRI. FURTHER COMPLICATING THE FCST FROM FRI ONWARD IS THAT ENSEMBLES PERSIST IN SHOWING SIGNIFICANT SPREAD FOR UPSTREAM PAC FLOW. THIS WILL IMPACT THE EVOLUTION OF THE SHRTWV REACHING WRN CANADA AND THEN HOW THIS ENERGY PLUS THAT FROM THE EJECTING UPR LOW WILL PROGRESS EWD ACROSS CANADA. THE PREFERRED BLEND YIELDS A GOOD INTERMEDIATE SOLN WITH REASONABLE CONTINUITY IN LIGHT OF THE FCST UNCERTAINTIES. FARTHER EWD GUIDANCE IS IN THE PROCESS OF TRENDING SOMEWHAT SEWD WITH A CANADIAN FRONT EXPECTED TO SAG INTO THE NRN TIER STATES LATE IN THE WEEK AND EVENTUALLY REACH THE NORTHEAST. SOME GFS RUNS HAVE TENDED TO BE ON THE AMPLIFIED SIDE OF THE SPREAD WITH THE SUPPORTING UPR DYNAMICS THOUGH. THE PREFERRED INTERMEDIATE FCST BALANCES RECENT TRENDS THAT COULD BE SUPPORTIVE OF FARTHER SWD GFS FRONTAL POSN IN PRINCIPLE WHILE ACCOUNTING FOR LESS FAVORABLE COMPARISON TO MOST OTHER SOLNS THUS FAR. THIS SYSTEM WILL RELOAD THE ERN CANADA/NERN U.S. PART OF THE ERN TROUGH WHILE THE SRN PART OF THE OVERALL TROUGH SHOULD PERSIST OVER THE SOUTHEAST AND PSBLY FORM A WEAK UPR LOW DURING THE WEEKEND. SMALLER SCALE DETAILS FOR THE SYSTEM OVER THE NORTHEAST ON WED WILL TAKE A LITTLE MORE TIME TO WORK OUT BUT THERE IS BETTER THAN AVG AGREEMENT WITH THE TRAILING FRONT THAT SHOULD SETTLE OFF THE SERN COAST AND OVER NRN FLORIA/GULF OF MEXICO. ...SENSIBLE WEATHER HIGHLIGHTS... UPR LOW EJECTING FROM OFF THE NRN CA COAST MAY GENERATE AN EPISODE OF ENHANCED RNFL OVER THE EXTREME NORTHWEST LATE IN THE WEEK. AS ASSOC CANADA LOW PRES DRAGS A COLD FRONT EWD... SHWRS/TSTMS SHOULD INCREASE OVER THE NRN PLAINS AND VICINITY NEXT WEEKEND. SOME OF THE MONSOONAL MSTR AIDING PERIODS OF CONVECTION OVER THE FOUR CORNERS STATES MAY FEED N/NE AHEAD OF THE FRONT LEADING TO LOCALLY HVY CONVECTION. HOWEVER NOTE THAT CONFIDENCE IN A SPECIFIC SCENARIO IS CURRENTLY ON THE LOW SIDE GIVEN UNCERTAINTY IN NRN TIER FLOW DETAILS BY SAT-SUN. THE NORTHEAST SHOULD TREND SOMEWHAT DRIER FOR A TIME WITH THE DEPARTURE OF WED LOW PRES THOUGH LINGERING UPR TROUGHING MAY SUPPORT SCT DIURNAL CONVECTION. AN UPSTREAM FRONT CROSSING THE NRN TIER AND HEADING TOWARD THE NORTHEAST WILL LIKELY BE ACCOMPANIED BY SOME SHWRS/TSTMS FROM THU ONWARD. FARTHER SWD THE FRONT LIKELY TO STALL OVER NRN FL/GULF OF MEXICO MAY SUPPORT A MULTI-DAY PERIOD OF ENHANCED RNFL MOST LIKELY OVER FL. SOME ACTIVITY MAY ALSO EXTEND ALONG THE GULF/SOUTHEAST COASTS FOR AT LEAST A PART OF THE FCST PERIOD. BY NEXT WEEKEND THE EVOLUTION OF LINGERING ENERGY ALOFT OVER THE SOUTHEAST MAY PLAY A ROLE IN CONVECTIVE DEVELOPMENT. AN AREA OF HIGHEST TEMPS RELATIVE TO NORMAL SHOULD PROGRESS FROM THE INTERIOR NORTHWEST... WHERE PLUS 10-15F OR SO ANOMALIES ARE PSBL ON WED... ACROSS THE NRN TIER STATES. SRN PLAINS/LWR MS VLY HEAT AT THE START OF THE PERIOD SHOULD GRADUALLY MODERATE BUT HIGHS MAY REMAIN MODESTLY ABOVE NORMAL THROUGH NEXT WEEKEND. SYSTEM BRUSHING THE NORTHWEST LATE IN THE WEEK WILL BRING A BRIEF COOLER SPELL TO THAT REGION WHILE TEMPS OVER MUCH OF THE EAST SHOULD REBOUND TO NEAR/SLIGHTLY ABOVE NORMAL AFTER SEEING UP TO MINUS 5-10F ANOMALIES FOR HIGHS WED. RAUSCH