EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 152 AM EST SAT NOV 18 2017 VALID 12Z TUE NOV 21 2017 - 12Z SAT NOV 25 2017 ...GUIDANCE/UNCERTAINTY PREFERENCES...... A DYNAMIC LEAD MID-UPPER LEVEL TROUGH/HEIGHT FALLS PROGRESS FROM THE UPPER MIDWEST THROUGH THE GREAT LAKES/NERN US TUE-WED WITHIN NRN STREAM FLOW. THIS SUPPORTS A DEEPENED CLIPPER LOW TRACK AND SWATH OF PCPN ALONG THE US/CANADIAN BORDER ALONG WITH A REINFORCING COOLING SURGE AND A PERIOD OF LAKE EFFECT SNOWS IN THE WAKE OF SYSTEM PASSAGE. SEVERAL LESS CERTAIN WEAKER PROGRESSIVE SYSTEMS ARE SLATED TO FOLLOW LATER NEXT WEEK WITHIN THIS NRN STREAM FLOW. THE EXTENT OF DIGGING OF EMBEDDED SRN STREAM IMPULSES UNDERNEATH TO THE LEE OF A BUILDING WARMING WRN US MID-UPPER LEVEL RIDGE EARLY NEXT WEEK AND MID-LATER NEXT WEEK POTENTIAL SRN STREAM TROUGH/LOW SEPARATION OVER THE GULF COAST REMAINS FURTHER COMPLICATED BY POTENTIAL FOR NRN STREAM INTERACTION IN SOME SOLUTIONS. FORECAST SPREAD AND UNCERTAINTY REMAINS ABOVE NORMAL ALONG WITH MODEL RUN TO RUN VARIANCE. OF THE ENSEMBLES...PREFER THE ECENS THAT SHOWS MORE FLOW SEPARATION AND WEATHER FOCUS THAN THE GEFS/CANADIAN/NAEFS. THIS MATCHES WPC CONTINUITY AND FITS THE OVERALL FLOW AMPLIFICATION UPSTREAM AS PER RECENT MODEL TRENDS. MEANWHILE...CONTINUED INLAND FLOW OF PACIFIC IMPULSES FROM AN AMPLIFIED OFFSHORE MID-UPPER LEVEL MEAN TROUGH PROLONGS A WET PATTERN THAT INCLUDES ELEVATION SNOWS OVER THE NWRN US THROUGH THE EXTENDED THANKSGIVING BREAK...ALBEIT WITH QUICKLY GROWING TIMING UNCERTAINTY. OVERALL...THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A BLEND OF THE 12 UTC GFS/ECMWF AND GEFS/ECMWF ENSEMBLES INTO THANKSGIVING BEFORE TRANSITIONING TO AN ECMWF ENSEMBLE MEAN CENTERED SOLUTION BY DAYS 6/7 (NEXT FRI-SAT) THAT MAINTAINS MAX WPC CONTINUIY. ...WEATHER HIGHLIGHTS... WET FLOW CONTINUES FOR THE PACIFIC NW WITH OCCASIONALLY HEAVY DAILY RAINS AND LOCALLY HEAVY ELEVATION SNOWS. UPPER RIDGING WILL SUPPORT ABOVE AVERAGE TEMPERATURES FROM THE SOUTHWEST THROUGH THE SOUTHERN GREAT BASIN/ROCKIES AND PLAINS...BUT COOLER THAN AVERAGE IN THE EASTERN US BEHIND A COLD FRONT. THERE IS A GOOD CHANCE FOR APPRECIABLE PRECIPITATION ALONG THE GULF COAST AS LOW PRESSURE MEANDERS ALONG A SLOW MOVING FRONT. EXPECT SOME RAIN/SNOW AROUND THE GREAT LAKES BUT GENERALLY NO PRECIPITATION FROM THE SOUTHWEST TO THE PLAINS AND MS VALLEY. ...THANKSGIVING FORECAST... GENERALLY QUIET FOR MOST OF THE LOWER 48. PRECIPITATION WILL BE MOST CONCENTRATED IN THE PACIFIC NORTHWEST INTO NORTHERN CALIFORNIA AS WELL AS NORTHERN IDAHO/WESTERN MONTANA/NW WYOMING. ORGANIZED RAIN IS ALSO QUITE POSSIBLE ALONG THE GULF COAST FROM TEXAS EASTWARD TO FLORIDA . RECORD HIGH TEMPS ARE POSSIBLE IN THE SOUTHWEST WITH WIDESPREAD 80S AND SOME 90S. SCHICHTEL