EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 200 AM EST WED JAN 13 2016 VALID 12Z SAT JAN 16 2016 - 12Z WED JAN 20 2016 ...OVERVIEW... BROAD TROUGHING WILL REMAIN CARVED OUT OVER THE EASTERN TWO-THIRDS OF THE NATION THIS WEEKEND AND INTO EARLY NEXT WEEK AS A DEEP UPPER VORTEX SINKING SOUTH FROM CANADA ROTATES OVER THE GREAT LAKES AND NORTHEAST. MULTIPLE SHORTWAVES ROUNDING THE BASE OF THE TROUGH WILL HAVE THE POTENTIAL TO TRIGGER SURFACE CYCLOGENESIS WHILE LIFTING NORTHEASTWARD TOWARDS THE WESTERN ATLANTIC...WITH AT LEAST ONE COASTAL STORM LOOKING LIKELY FOR THE NORTHEAST THIS WEEKEND. MEAN RIDGING OVER THE WESTERN U.S. SHOULD GRADUALLY SHIFT EASTWARD EARLY NEXT WEEK...WHILE IMPULSES OF ENERGY WITHIN THE MEAN FLOW WILL CONTINUE TO MOVE INLAND OVER THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA BEFORE RIPPLING DOWNSTREAM INTO THE INTERMOUNTAIN WEST. ...MODEL EVALUATION AND PREFERENCES... MODELS ARE STILL SHOWING A LOT OF SPREAD WITH THE EVOLUTION OF THE DEEP VORTEX ROTATING OVER THE GREAT LAKES AND NORTHEAST THIS WEEKEND...RESULTING IN A LOT OF UNCERTAINTY EARLY IN THE PERIOD WITH THE EXACT DETAILS OF A COASTAL STORM LIFTING AWAY FROM NEW ENGLAND...ARCTIC AIR PLUNGING SOUTHEASTWARD OUT OF THE NORTH CENTRAL U.S....AS WELL AS SHORTWAVE ENERGY PROGRESSING FROM TEXAS TO THE NORTHERN GULF OF MEXICO. LATER IN THE PERIOD...THE FOCUS FOR UNCERTAINTY OVER THE LOWER 48 SHIFTS INTO THE WESTERN U.S....WHERE MODELS HAVE BEEN HINTING AT POSSIBLY AMPLIFYING AN UPPER TROUGH OVER THE SOUTHWEST BY THE MIDDLE OF NEXT WEEK. THE WPC DAY 3-7 FORECAST STARTED WITH A BLEND OF ENSEMBLE MEAN GUIDANCE...WITH MORE WEIGHT GIVEN TO THE ECMWF ENSEMBLE MEAN SINCE MODELS HAVE GENERAL BEEN TRENDING TOWARDS ITS FASTER SOLUTION WITH DROPPING THE CLOSED VORTEX OUT OF CANADA THIS WEEKEND. GERHARDT