EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 129 AM EST SUN NOV 15 2015 VALID 12Z WED NOV 18 2015 - 12Z SUN NOV 22 2015 ...OVERVIEW... A MIGRATORY UPPER-LEVEL TROUGH --- CURRENTLY WEST OF THE CENTRAL CALIFORNIA COAST--- WILL GENERATE A SURFACE CYCLONE TRACK THAT PASSES FROM THE FOUR CORNERS REGION TO LAKE SUPERIOR DURING THIS MEDIUM RANGE PERIOD. ALONG AND AHEAD OF THIS SYSTEM --- ACTIVE WEATHER IS ANTICIPATED WITH A BROAD FETCH OF GULF OF MEXICO MOISTURE LIKELY TO BE TRANSPORTED NORTHWARD INTO NORTHEASTERN CANADA AND NEW ENGLAND --- BEFORE THE SYSTEM EXITS INTO THE WESTERN ATLANTIC BASIN ON FRIDAY. ...MODEL PREFERENCES... IN GENERAL...THE 14/12Z ECENS AND NAEFS MEANS SEEMED THE BEST FIT ACROSS THE LOWER 48 DURING THE ENTIRE MEDIUM RANGE PERIOD. AND FOR THE MOST PART... THIS PACKAGE WAS ABLE TO DISCERN SOME SMALLER-SCALE DETAILS FROM THE 14/12Z ECMWF THROUGH THE END OF DAY 5 (21/00Z). THIS DETERMINISTIC RUN SHOULD HANDLE ASPECTS OF THE PRECIPITATION DETAILS ASSOCIATED WITH THE SURFACE CYCLONE TRACK THROUGH THE CENTRAL AND EASTERN PORTIONS OF THE CONTINENT. ...UNCERTAINTY ASSESSMENT... THERE ARE ASPECTS OF EACH 14/12Z DETERMINISTIC RUN (GFS/ECMWF AND CANADIAN) WORTH MENTIONING --- SINCE THEIR DIFFERENCES --- HELD SUBTLE SENSIBLE WEATHER DIFFERENCES. IN THE EAST... THE 14/12Z DETERMINISTIC CANADIAN IS THE MORE AGGRESSIVE SOLUTION ACROSS THE NORTHEAST AND NEW ENGLAND WITH COLD ADVECTION BEHIND THE FRONT ON THURSDAY NIGHT...FOLLOWED BY THE 14/12Z ECMWF. THE GFS WOULD BE THE WEAKEST FRONTAL PASSAGE SOLUTION ALONG THE ENTIRE EAST COAST. UPSTREAM IN THE WEST... ASPECTS OF THE GFS/ECMWF SOLUTIONS WOULD SUGGEST SOME ARCTIC-MODIFIED AIR MAKES ITS WAY INTO THE PACIFIC NORTHWEST. AND THEIR 250MB JET-LEVEL FORECASTS REASONABLE HANDLE THE FAST-MOVING WESTERLY COMPONENT TO THE FLOW ACROSS SOUTHERN IDAHO AND SOUTHERN WYOMING FOR DAYS 5-6 --- WHICH CONTINUE TO CARVE OUT THE WESTERN SIDE OF THE UPPER-LEVEL TROUGH'S BASE. AND UNLIKE THE CANADIAN... THE GFS AND ECMWF WOULD SUGGEST A PIECE OF THE COLD ALASKAN AIRMASS BECOMES DISLODGED AND MAKES A SOUTHWARD TREK ACROSS THE CANADIAN ROCKIES AND INTO THE UPPER MISSOURI VALLEY. THIS WOULD REALLY BE THE ONLY PORTION OF THE LOWER 48 --- SUSCEPTIBLE TO BELOW NORMAL TEMPERATURES --- DURING THIS MEDIUM RANGE PERIOD. ACROSS THE SOUTH... THE BULK OF THE GUIDANCE CONTINUES TO SUPPORT LARGE RAINFALL NUMBERS FOR MISSISSIPPI...ALABAMA PORTIONS OF KENTUCKY AND TENNESSEE... ALONG WITH MUCH OF THE SOUTHERN APPALACHIANS AND PIEDMONT. THE SOUTHERN BRANCH OF THE JET REMAINS A KEY COMPONENT OF THIS RAINFALL EVENT AND MAINTAINS A SUBSTANTIAL SOURCE OF LIFT INTO THE HIGHER LATITUDES. AND WHAT HAS BEEN THE CASE FOR SEVERAL DAYS NOW --- THE DETERMINISTIC RUNS APPEARED TO HAVE A GOOD GRASP ON THE INTERACTION BETWEEN NORTHERN AND SOUTHERN STREAM JET STREAKS. ...SENSIBLE WEATHER HIGHLIGHTS... WIDESPREAD PRECIPITATION AND RATHER MILD MID-NOVEMBER TEMPERATURES MIGRATE FROM THE MISSISSIPPI RIVER TO THE EAST COAST DAYS 3-4 (WED-THU) ALONG AND AHEAD OF A SURFACE FRONT. SOME COOLER TEMPERATURES BEHIND THE FRONT... BUT THE MORE APPRECIABLE CHANGE WILL BE NOTED ACROSS FLORIDA. ONSHORE FLOW AND JET-DRIVEN PRECIPITATION FOR THE WINDWARD CASCADES AND NORTHERN CONTINENTAL DIVIDE (WITH HIGH-ELEVATION SNOWS) FOR DAYS 4-5 --- THEN SPREADING THE COOLER CANADIAN AIRMASS DOWNSTREAM (EAST) OF THE NORTHERN DIVIDE --- AND INTO THE NORTH CENTRAL ROCKIES...FAR NORTHERN PLAINS AND UPPER GREAT LAKES FOR DAYS 6-7. VOJTESAK