EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1215 AM EST THU DEC 07 2017 VALID 12Z SUN DEC 10 2017 - 12Z THU DEC 14 2017 ...OVERVIEW... SECOND VERSE, SAME AS THE FIRST. THE WESTERN RIDGE/EASTERN TROUGH REMAINS LOCKED IN PLACE. THIS WILL CONTINUE THE STABLE SYNOPTIC PATTERN OF MILD/DRY IN THE WEST, A TRANSITION ZONE OF TEMPERATURES IN THE CENTRAL STATES (PLAINS TO MISSISSIPPI VALLEY), AND COLD IN THE EAST WITH PRECIPITATION FOCUSED MOSTLY AROUND THE GREAT LAKES AND THEN THE NORTHEAST NEXT WED/THU AS A POTENTIAL COASTAL STORM DEVELOPS. ...GUIDANCE PREFERENCES AND PREDICTABILITY ASSESSMENTS... CONTINUED WITH A DETERMINISTIC CONSENSUS BLEND FOR THE FORECAST WITH A TREND TOWARD THE ENSEMBLE MEANS LATER IN THE PERIOD. THOUGH THE 12Z UKMET/CANADIAN WERE ON THE EXTREME SIDE OF THE ENSEMBLE SPREAD IN THE SHORT TERM, A MINOR WEIGHTING WITH THE GFS/ECMWF YIELDED A GOOD STARTING POINT AS ONE COASTAL LOW EXITS AWAY FROM MAINE ON SUNDAY. THEREAFTER, THE 12Z CANADIAN WAS FAVORED THROUGH MUCH OF THE PERIOD AS THE 12Z ECMWF YET AGAIN SHOWED A PACIFIC UPPER LOW TRYING TO PUNCH INTO THE RIDGE. THOUGH IT IS CERTAINLY POSSIBLE TO SNEAK A WEAK SYSTEM UNDERNEATH THE CORE OF POSITIVE HEIGHT ANOMALIES (LOCATED IN BRITISH COLUMBIA) OPTED TO DOWNPLAY THIS FEATURE AGAIN UNTIL MORE SUPPORT IS SEEN. THE WEAKER CANADIAN/GFS WERE PREFERRED THERE. BY NEXT WED/THU, GUIDANCE CONTINUES TO ADVERTISE A MORE ROBUST COASTAL DEVELOPMENT OFFSHORE THE MID-ATLANTIC WITH A TRACK JUST OFF THE NEW ENGLAND COAST. THIS WOULD BE A RAIN/SNOW EVENT FOR NEW ENGLAND AS IT WINDS UP INTO SOUTHEASTERN CANADA. ENSEMBLES HAVE BEEN CONSISTENT FOR SEVERAL DAYS THOUGH THIS DOES DEPEND ON SHORTWAVES STILL IN THE CENTRAL PACIFIC. AS SUCH, HOW THIS EVOLVES IS UNCERTAIN BUT THE 12Z CANADIAN OFFERED A REASONABLE SOLUTION NEAR THE CONSENSUS POSITION NEXT WED. ...WEATHER HIGHLIGHTS... SEVERAL CLIPPERS WILL SWING THROUGH THE EAST WITH A RENEWED COLD SHOT OF CANADIAN AIR BUT GENERALLY LIGHT PRECIP -- THE EXCEPTION WILL BE AROUND THE GREAT LAKES AND ALONG THE TRACK OF THE NORTHERN STREAM SYSTEM. TEMPERATURES WILL BE ABOUT 5-20 DEGREES ABOVE AVERAGE IN THE WEST (OUTSIDE THE INTERIOR VALLEY AREAS OF WA/OR UNDER AN INVERSION) AND ABOUT 5-15 DEGREES BELOW AVERAGE IN THE EAST. FRACASSO