EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1203 PM EDT FRI AUG 07 2015 VALID 12Z MON AUG 10 2015 - 12Z FRI AUG 14 2015 ...OVERVIEW... FLOW WILL BECOME INCREASINGLY AMPLIFIED OVER THE LOWER 48 NEXT WEEK. THE PERSISTENT RIDGE ANCHORED OVER THE SOUTH CENTRAL U.S. SHOULD STRENGTHEN AS IT DRIFTS FROM THE SOUTHERN PLAINS TO THE ROCKIES. ON EITHER SIDE OF THE BUILDING RIDGE...MEAN TROUGHING SHOULD SETTLE IN ON BOTH THE WEST AND EAST COASTS. AT THE SURFACE...A COLD FRONT OVER THE OHIO VALLEY AND MIDDLE MISSISSIPPI VALLEY ON MONDAY WILL STEADILY PRESS SOUTHEASTWARD TOWARDS THE APPALACHIANS AND GULF COAST BEFORE STALLING OUT ALONG THE EASTERN SEABOARD LATER NEXT WEEK. OUT WEST...A FRONTAL BOUNDARY INITIALLY STRETCHED THROUGH THE NORTHWEST WILL STRUGGLE TO PROGRESS INLAND AS THE DOWNSTREAM RIDGE RIDGE AMPLIFIES OVER THE SOUTH CENTRAL U.S.. ...GUIDANCE EVALUATION/PREFERENCES... THE GREATEST UNCERTAINTY IN THE FORECAST CONTINUES TO BE WITH THE EVOLUTION OF A CLOSED LOW DROPPING DOWN FROM THE BRITISH COLUMBIA COAST EARLY NEXT WEEK. THE 00Z GFS/ECMWF/UKMET WERE IN AGREEMENT WITH SINKING THE DEEP VORTEX SOUTHWARD TOWARDS THE NORTHERN CALIFORNIA COAST...BUT THEN THE MODEL SPREAD INCREASES QUICKLY BY THE MIDDLE OF THE WEEK WITH PROGRESSING THE UPPER LOW INLAND OVER THE WESTERN U.S.. THE 00Z CMC IMMEDIATELY BRINGS THE UPPER LOW INTO THE NORTHWEST RATHER THAN DROPPING IT DOWN TOWARDS THE CALIFORNIA COAST...WHILE THE 06Z GFS SWINGS THE CORE OF THE ENERGY NORTHEASTWARD THROUGH SOUTHWEST CANADA. EVEN THE ENSEMBLE MEANS ARE OFFERING VARYING SOLUTIONS WITH THIS FEATURE. ANOTHER AREA OF UNCERTAINTY IN THE FORECAST IS WITH POSSIBLE SURFACE WAVES DEVELOPING ALONG THE FRONTAL BOUNDARY PUSHING TOWARDS THE APPALACHIANS AND STALLING OFF THE EAST COAST. THE WPC DAY 3-7 FORECAST STARTED WITH THE 00Z ECMWF ENSEMBLE MEAN...WHICH APPEARED TO MATCH BEST WITH CONTINUTITY AND WAS IN THE MIDDLE OF THE CURRENT MODEL SPREAD WITH BOTH THE EVOLUTION OF THE CLOSED LOW DROPPING DOWN FROM THE BRITISH COLUMBIA COAST AND WITH SURFACE WAVES DEVELOPING ALONG THE FRONT IN THE EAST. GERHARDT ...SENSIBLE WEATHER HIGHLIGHTS/THREATS... LOW PRESSURE/FRONT PUSHING THROUGH THE EAST WILL PROVIDE A FOCUS FOR LOCALLY ENHANCED RNFL... WITH BEST ORGANIZED ACTIVITY SETTLING OVER THE VICINITY OF FLORIDA AND THE SERN COAST BY LATE IN THE WEEK AS THE FRONT DECELERATES. BEHIND THE FRONT THE LINGERING UPR TROUGH MAY AID THE DEVELOPMENT OF SCT DIURNAL CONVECTION ESPECIALLY OVER THE NORTHEAST UNDER LOWEST HGTS ALOFT. ENERGY WITHIN THE WEST COAST TROUGH WILL ALSO SUPPORT PERIODS OF CONVECTION OVER THE NORTHWEST... BUT WITH CONSIDERABLE UNCERTAINTY AS TO TIMING/EXTENT OF DOWNSTREAM PROGRESSION AFTER WED. MEANWHILE MONSOONAL FLOW WILL SUPPORT SHWRS/TSTMS FROM THE SOUTHWEST INTO THE FOUR CORNERS/SRN ROCKIES AND PSBLY EXTENDING INTO PORTIONS OF THE PLAINS. EXPECT WELL ABOVE NORMAL TEMPS ACROSS THE SRN TIER AT THE START OF THE WEEK... WITH PLUS 10-15F ANOMALIES FOR HIGHS MOST LIKELY OVER/NEAR THE LOWER MS VLY. SOME DAILY RECORDS ARE PSBL. IT SHOULD REMAIN VERY WARM/HOT FROM THE LWR MS VLY INTO SRN HIGH PLAINS FOR THE REST OF THE PERIOD BUT WITH LESSER ANOMALIES. UNSETTLED CONDS SHOULD LEAD TO NEAR/BELOW NORMAL HIGHS OVER THE WEST WHILE NEAR TO BELOW NORMAL READINGS SHOULD SETTLE IN BEHIND THE ERN FRONT. IN-BETWEEN EXPECT MOSTLY ABOVE NORMAL READINGS OVER THE NRN HIGH PLAINS. RAUSCH