EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 214 AM EST SAT NOV 19 2016 VALID 12Z TUE NOV 22 2016 - 12Z SAT NOV 26 2016 ...LATEST GUIDANCE AND PREDICTABILITY ASSESSMENT... GFS/GEFS MEANS AND ECMWF/ECMWF ENSEMBLE MEANS ALONG WITH THE UKMET OVER THE PAST 24 HOURS HAVE OVERALL CONVERGED UPON A SEEMINGLY REASONABLE AND CLUSTERED MEDIUM RANGE SOLUTION FOR MOST OF THE PERIOD ACROSS THE NATION. THIS BOLSTERS FORECAST CONFIDENCE TO ABOVE NORMAL LEVELS EVEN AS THE PATTERN GRADUALLY BECOMES MORE PROGRESSIVE. THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM THESE GUIDANCE SOURCES AND CONTINUITY. OVERALL...WPC MANUALLY PRODUCED MEDIUM RANGE SURFACE FRONTS/PRESSURES AND 500 MB PROGS ALONG WITH THE DAYS 4-7 QPF AND WINTER WEATHER OUTLOOK PROBABILITIES PROVIDE THE DETAILS. ...WEATHER FLOW HIGHLIGHTS/THREATS... A LEAD AND COOLING CLOSED LOW NUDGED OUT OVER ERN CANADA MON/TUE WILL FEATURE STRONG COLD ADVECTION AND LINGERING LAKE EFFECT SNOW OFF LAKES ERIE/ONTARIO/CHAMPLAIN AND FAVORED TERRAIN OF THE INTERIOR NORTHEAST. THE UPPER VORTEX THEN SHIFTS DOWNSTREAM TO ALLOW UPPER HEIGHTS TO REBOUND OVER THE ERN US. MEANWHILE...A DYNAMIC SOUTHERN STREAM SHORT WAVE TROUGH WILL EJECT OUT INTO THE PLAINS BY TUE AND NORTHEASTWARD TO THE GREAT LAKES/MS VALLEY/MIDWEST MIDWEEK. THE ASSOCIATED DEEPENED SURFACE LOW/SYSTEM SHOULD REACH THE NORTHEASTERN US/MID-ATLANTIC THU...WITH A DEVELOPING TRIPLE POINT COASTAL LOW TAKING OVER LATER THU INTO SAT. AS THE SYSTEM PUSHES OUT INTO THE MIDWEST ON TUE...EXPECT A RELATIVELY NARROW ZONE OF SHOWERS/STORMS ALONG THE FRONT AND SOLID COMMA HEAD/DEFORMATION ZONE OF MODERATE TO HEAVY RAIN AND TRANSITION ZONE OVER TO SNOW ACROSS PARTS OF THE UPPER MIDWEST/GREAT LAKES. THE FRONTAL ZONE WILL CONTINUE TO ADVANCE DOWNSTREAM WITH JUST A NARROW PLUME OF MOISTURE CONTENT AHEAD OF THE LOW/FRONT FROM THE SOUTH TO GREAT LAKES. ON THU THOUGH...UPPER DYNAMICS TRANSFERS TO THE NRN MID-ATL/NORTHEAST COAST TO ALLOW A COASTAL LOW TO DEVELOP WHICH COULD PRODUCE A SPIKE OF QPF BEFORE THE BULK OF MOISTURE SHIFTS OFFSHORE AND UP INTO WINTERY NEW ENGLAND FRI/SAT WHERE THERE IS POTENTIAL FOR SOME HEAVIER LOCAL SNOW/ICE. UPSTREAM...A WET FLOW PATTERN REMAINS QUITE ACTIVE WITH AN AMPLIFIED MEAN MID-UPPER NERN PACIFIC THROUGH PROVIDING THE PUNCH AS A SERIES OF POTENT SHORT WAVE IMPULSES TRANSPORT PACIFIC MOISTURE AND HEAVY PCPN ACROSS THE PAC NW COAST/NRN CA AND TO A LESSER EXTENT FURTHER INLAND TO THE NRN INTERMOUNTAIN WEST/ROCKIES INCLUDING TERRAIN ENHANCED SNOWS. SYSTEM ENERGY THEN WORKING OVER THE CENTER OF THE COUNTRY WILL NOT HAVE MUCH MOISTURE TO WORK WITH THERE. SCHICHTEL