EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1059 AM EST TUE NOV 17 2015 VALID 12Z FRI NOV 20 2015 - 12Z TUE NOV 24 2015 ...MODEL PREFERENCES AND UNCERTAINTY... IN THE BEGINNING OF THE PERIOD...THERE WAS DECENT MODEL AGREEMENT AMONGST THE OPERATIONAL RUNS INTO SATURDAY MORNING SO A NEARLY 50/50 BLEND OF THE 06Z GFS/00Z ECMWF SEEMED REASONABLE. MODELS BEGIN TO DIVERGE BY THE SECOND HALF OF DAY 4/SAT WITH THE ECMWF/ECENS MUCH SLOWER AND DEEPER WITH THE TROUGH ACROSS THE MIDWEST THAN THE GFS/GEFS WHICH SUPPORTS A MUCH MORE PROGRESSIVE SOLUTION BY DAY 5 AND BEYOND. RUN TO RUN CONTINUITY AMONGST THE OPERATIONAL MODELS IS NOT GREAT...SO PREFER AN ENSEMBLES BASED FORECAST APPROACH GIVEN ABOVE NORMAL UNCERTAINTY. WE DID WANT TO EMPHASIZE THE POSSIBILITY OF A STRONGER/DEEPER SOLUTION LIKE DEPICTED BY THE EUROPEAN...SO A BLEND OF THE DEEPER 00Z ECENS WITH THE 00Z/06Z NAEFS/GEFS PROVIDED US WITH THE SOLUTION WE WERE LOOKING FOR. LATER IN THE PERIOD UPSTREAM...SUBSTANTIAL MODEL DIFFERENCES/UNCERTAINTY EXIST NOT ONLY WITH TROUGHING ALOFT OFF CALIFORNIA THIS WEEKEND...BUT MORE SUBSTANTIALLY WITH NORTHERN STREAM TROUGHING DIGGING INTO/OFFSHORE THE NORTHWEST U.S. EARLY NEXT WEEK. OUR ENSEMBLE BLEND PUTS US ON THE SLIGHTLY MORE AMPLIFIED SIDE OF SOLUTIONS WITH TROUGH AMPLITUDE. THIS SEEMS REASONABLE GIVEN THE MODEL CONSENSUS OF MORE AMPLIFIED RIDGING UPSTREAM. THIS COULD SUPPORT MODEST PRECIPITATION FOR THE NORTHWESTERN U.S.. ...OVERVIEW AND SENSIBLE WEATHER HIGHLIGHTS/THREATS... WIDESPREAD RAINFALL ASSOCIATED WITH A FRONT PUSHING OFF THE EAST COAST MAY LINGER ACROSS NEW ENGLAND AND DOWN ACROSS THE GULF COAST STATES INTO THE WEEKEND...BUT QUICKLY DRIES OUT BEHIND THE FRONT. UPSTREAM FROM THIS...A LONGWAVE MEAN TROUGH DOMINATES USHERING IN A COOLER CANADIAN AIRMASS AND RELATIVELY DRY WEATHER PATTERN ACROSS MUCH OF THE COUNTRY IN THE MEDIUM RANGE PERIOD. AN EXCEPTION TO THIS COULD BE WITH AMPLIFICATION OF THE TROUGH THIS WEEKEND TRANSLATING TO SOME DECENT PRECIPITATION ACROSS THE GREAT LAKES/MIDWEST AND EASTERN U.S. DURING THE WEEKEND. ESPECIALLY ACROSS THE GREAT LAKES...ORGANIZED SNOW SHOWERS ARE LIKELY. SANTORELLI/SCHICHTEL