EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1135 AM EDT WED AUG 31 2016 VALID 12Z SAT SEP 03 2016 - 12Z WED SEP 07 2016 ...STRENGTHENING TROPICAL DEPRESSION NINE EXPECTED TO AFFECT THE EASTERN SEABOARD... ...OVERVIEW... TWO AREAS WILL BE OF INTEREST DURING THE PERIOD... THE EAST COAST WHICH MAY SEE SOME EFFECTS FROM T.D. NINE EXTENDING FROM THE SHORT RANGE PERIOD AND THEN FROM THE NRN HALF OF THE PLAINS INTO THE UPR/WRN GREAT LAKES WHERE A SLOW MOVING WAVY FRONT WILL PROVIDE A FOCUS FOR A POTENTIALLY MULTI-DAY EVENT OF LOCALLY HVY AND IN SOME CASES STRONG CONVECTION. BOTH AREAS/EVOLUTIONS HAVE THEIR UNCERTAINTIES BUT GUIDANCE REMAINS GENERALLY WELL CLUSTERED FOR THE LARGE SCALE PATTERN CONSISTING OF A STRONG EASTERN PAC RIDGE... WRN U.S. TROUGH THAT SHOULD GRADUALLY BROADEN WITH TIME... AND A BUILDING RIDGE ACROSS EASTERN NORTH AMERICA. ...GUIDANCE/UNCERTAINTY ASSESSMENT... THE 00Z ECMWF/06Z GEFS PROVIDED A BASIS FOR THE FCST. A BLEND OF THESE SOLUTIONS ALLOWS FOR MANAGEABLE ADJUSTMENTS TO ACCOMMODATE THE OFFICIAL NHC FCST FOR T.D. NINE AND ITS EVENTUAL EXTRATROPICAL EVOLUTION OVER THE WESTERN ATLANTIC BY DAY 4. THIS BLEND ALSO REFLECTS A FASTER TREND AMONG THE GUIDANCE FOR THE SYSTEM CROSSING CANADA AND ITS COLD FRONT EXTENDING INTO THE NORTHERN PLAINS. GUIDANCE TRENDS FOR T.D. NINE OVER THE PAST DAY HAVE BEEN WESTWARD A BIT CLOSER TO THE EAST COAST BUT NOT TO THE EXTENT OF THE WESTERN SIDE OF THE ENVELOPE THAT INCLUDED THE 00Z UKMET/CMC AND 12Z NAM. IT WILL BE AROUND THE START OF THE PERIOD ON SAT WHEN T.D. NINE SHOULD BE IN THE PROCESS OF INTERACTING WITH NRN STREAM TROUGH ENERGY DROPPING SOUTHEASTWARD FROM THE GREAT LAKES. THE SYSTEM IS THEN FORECAST TO LIFT NORTHWARD BETWEEN THE BUILDING EASTERN U.S. RIDGE AND ANOTHER RIDGE TO THE E OF BERMUDA. PLACEMENT BETWEEN THESE RIDGES AND THE DEGREE OF INTERACTION WITH THE NORTHERN STREAM SHORTWAVE ENERGY WILL LIKELY PROVIDE SOME ONGOING FCST CHALLENGES FOR TRACK AND TIMING. FARTHER WEST... MODELS HAVE TRENDED FASTER AND SLIGHTLY MORE AMPLIFIED WITH SHORTWAVE ENERGY MOVING FROM THE ROCKIES INTO THE PLAINS BY DAYS 6/7. AS A RESULT THE EASTWARD PROGRESSION OF THE FRONTAL SYSTEM ACROSS THE CENTRAL U.S. IS A BIT FASTER WITH THIS FORECAST PACKAGE RELATIVE TO THE PREVIOUS ONE. ULTIMATELY THE TIMING OF THIS SHORTWAVE ENERGY WILL BE RELIANT ON HOW QUICKLY A CLOSED UPPER LOW OVER THE ALEUTIANS BREAKS DOWN AND EJECTS ENERGY EASTWARD AROUND NORTHERN SIDE OF THE EAST PACIFIC RIDGE. ...WEATHER HIGHLIGHTS/THREATS... THOSE WITH INTERESTS ALONG THE MID ATLC/NORTHEAST COAST SHOULD CONTINUE TO MONITOR FCSTS FOR T.D. NINE AND ITS EVENTUAL EXTRATROPICAL EVOLUTION. COASTAL AREAS MAY SEE STRONG WINDS AND POTENTIALLY HEAVY RAINFALL DEPENDING ON EXACT TRACK OF THE SYSTEM. FARTHER SWD A LINGERING FRONT NEAR THE ERN GULF COAST AND ACROSS FLORIDA MAY PROVIDE SOME ADDED FOCUS FOR DIURNALLY ENHANCED CONVECTION. MOIST FLOW MAY ALSO PROMOTE AREAS OF RAINFALL ALONG/INLAND FROM THE WRN HALF OF THE GULF COAST. ASIDE FROM RUN TO RUN ADJUSTMENTS IN SPECIFICS... FORECASTS HAVE BEEN FAIRLY CONSISTENT IN SHOWING HEAVY RAIN POTENTIAL FROM THE NRN-CNTRL PLAINS INTO THE MIDWEST/GREAT LAKES. TRAINING/REPEAT ACTIVITY WILL BE POSSIBLE AS ESTABLISHMENT OF SWLY FLOW ALOFT AHEAD OF THE WRN TROUGH ALOFT WILL RESULT IN VERY SLOW PROGRESS OF THE WAVY FRONT OVER THE NRN PLAINS. THE POTENTIAL FOR SOME CONVECTION TO BE STRONG IS BEING MONITORED BY SPC AS WELL. THE NRN ROCKIES/HIGH PLAINS WILL LIKELY SEE A PERIOD OF RAINFALL THAT COULD BE LOCALLY ENHANCED. EXPECT BELOW NORMAL TEMPS TO PREVAIL FROM MUCH OF THE WEST INTO THE NORTHERN PLAINS. CLOUDS AND RAINFALL MAY LEAD TO SOME MINUS 10-20F ANOMALIES FOR HIGHS OVER PARTS OF THE NRN ROCKIES/HIGH PLAINS EARLY NEXT WEEK. ON THE OTHER HAND THE UPPER RIDGE BUILDING INTO THE EAST SHOULD PROMOTE A WARMING TREND AND A BROAD AREA OF PLUS 5-15F ANOMALIES... AND PERHAPS LOCALLY HIGHER... FOR MAX TEMPS FROM MON ONWARD. TEMPS ALONG THE NRN HALF OF THE EAST COAST WILL BE SENSITIVE TO THE TRACK OF T.D. NINE. RYAN