EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 159 AM EST MON NOV 21 2016 VALID 12Z THU NOV 24 2016 - 12Z MON NOV 28 2016 ...GUIDANCE AND PREDICTABILITY ASSESSMENT... MEDIUM RANGE FORECAST CONFIDENCE/PREDICTABILITY SEEMS TO BE HEADING SOUTH OVER THE PAST DAY. IT WAS BOUND TO OCCUR GIVEN THE TRANSITION FROM A FAIRLY AMPLIFIED PATTERN TO A MUCH MORE PROGRESSIVE SOLUTION BUT AROUND THE START OF FRI THE OPERATIONAL AND ENSEMBLE GUIDANCE BEGIN TO DIVERGE. THE SOLID AGREEMENT ON THE QUICK PAC IMPULSES INTO THE WEST AND TRANSITIONING DOWNSTREAM INTO THE MIDWEST DISAPPEARS BUT THE OVERALL THEME REMAINS...A VERY WET MID WEEK THROUGH THE WEEKEND FOR THE PAC NW. THIS RESULTS IN A DOWNGRADE WITH CONFIDENCE FOR SOME PARTS OF THE FORECAST. WPC FOLLOWED A SOLID BLEND OF THE LATEST GFS/GEFS MEAN...NAEFS MEAN...AND ECMWF/ECMWF ENSEMBLE MEAN THROUGH FRI BEFORE TRANSITIONING TO AN ENSEMBLE APPROACH AT LONGER TIME FRAMES AMID QUICKLY GROWING FORECAST SPREAD. RELIED UPON THE NAEFS MEAN THAT COMPARED TO THE GFS/ECMWF ENSEMBLES BETTER INCORPORATED CONTINUITY AND LATEST DETERMINISTIC MODEL TRENDS FOR AN OVERALL LOWERING HEIGHTS PATTERN FOR THE LOWER 48 AND ESPECIALLY THROUGH THE SWRN US INTO NEXT WEEK BEFORE PERHAPS SIGNIFICANT EMERGENCE INTO THE S-CENTRAL PLAINS IN ABOUT A WEEK TBD. ...WEATHER FLOW HIGHLIGHTS/THREATS... A LEAD SHORTWAVE TROUGH MOVES EJECTS OUT FROM THE ERN US THU. AN ALREADY NARROW PLUME OF LOW LEVEL MOISTURE DIMINISHES UNTIL A TRIPLE POINT/COASTAL LOW DEVELOPS NEAR THE NRN MID-ATL/SRN NEW ENGLAND COAST...BUT EVEN THIS FEATURE HAS DE-AMPLIFIED SINCE YESTERDAY. MUCH QPF FOCUS IS OFFSHORE BY THU WITH THE DEVELOPING WAVE OF LOW PRESSURE BUT WINTERY MOISTURE/PCPN WILL LINGER ACROSS THE NORTHEAST/NEW ENGLAND. MEANWHILE UPSTREAM...ANOTHER DYNAMIC IMPULSE CRESTS THE ROCKIES THU AND INTO THE UPPER MIDWEST/GREAT LAKES ON FRI BEFORE MOVING OFFSHORE THE NORTHEAST ON SAT/SUN. ASSOCIATED CYCLOGENESIS/FRONTOGENESIS SEEMS MORE DEFINED WITH LATEST GUIDANCE AND SYSTEM TRACK SHOULD PRODUCE A STREAK OF LOCALLY HEAVIER QPF IN RESPONSE OF THIS RE-AFFIRMING WEAKNESS INCLUDING NRN TIER SNOWS. MEANWHILE MOST OF THE FOCUS WILL ACTUALLY BE UPSTREAM...AS THIS WAVE TRAIN OF WET PAC SYSTEMS INUNDATE THE PAC NW BEFORE MOVING OVER INTERMOUNTAIN WEST/ROCKIES. UNCERTAINTY WITH TIMING/SPECIFICS ARE LESS THAN STELLAR...BUT IT REMAINS LIKLEY THAT THE OVERALL FLOW PATTERN WILL BE EXTREMELY ACTIVE WITH AN AMPLIFIED MEAN MID-UPPER NERN PACIFIC TROUGH DRIVING A SERIES OF POTENT SHORT WAVE IMPULSES/HEIGHTS FALLS. THIS ALSO INCLUDES A WAVE OF PAC MOISTURE TRANSPORT TO FUEL A PERIOD OF VERY HEAVY PCPN INTO THE PAC NW COAST/NRN CA AND TO A LESSER EXTENT FURTHER INLAND TO THE NRN INTER-MOUNTAIN WEST/ROCKIES. QPF TOTALS FOR COASTAL WA/OR INTO NRN CA OVER THE FIVE DAYS RANGE FROM AREAL AVG AMOUNTS UPWARDS TO 6-8" ON OPERATIONAL SOLUTIONS AND 4-6" WITH ENSEMBLE MEANS. THIS PROLONGED EVENT COULD RESULT IN SOME HYDROLOGIC ISSUES. SCHICHTEL