EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 140 AM EST FRI NOV 20 2015 VALID 12Z MON NOV 23 2015 - 12Z FRI NOV 27 2015 ...OVERVIEW... LATEST GUIDANCE AS A WHOLE CONTINUES TO ADVERTISE A SURGE OF COLD AIR ACROSS THE WEST/PLAINS AS UPR TROUGHING AMPLIFIES OVER THE WEST. THERE IS A FAIR DEGREE OF CLUSTERING THAT IS COMPATIBLE WITH ESTABLISHED CONTINUITY... FAVORING MAINTENANCE OF A SIMILAR EVOLUTION THIS CYCLE. HOWEVER THE FULL ARRAY OF LATEST/RECENT SOLNS WOULD SUGGEST POTENTIAL FOR EVENTUAL CHANGES IN AT LEAST SOME OF THE DETAILS. WINTRY PCPN IN THE COLD AIR OVER THE WEST/PLAINS ALONG WITH RNFL IN THE LEADING WARM SECTOR MAY HINDER HOLIDAY TRAVEL OVER SOME AREAS. ...GUIDANCE EVALUATION/PREFERENCES... DURING DAYS 3-4 MON-TUE THERE IS A GOOD CONSENSUS REGARDING THE TROUGH AMPLIFYING INTO THE WEST/EMBEDDED CLOSED LOW REACHING THE NORTHWEST AS WELL AS THE DOWNSTREAM TROUGH ABOUT THE DEPART FROM THE ERN STATES. THIS AGREEMENT FAVORS LEANING MORE TOWARD THE 18Z GFS/12Z ECMWF RELATIVE TO THEIR RESPECTIVE ENSEMBLE MEANS EARLY IN THE FCST. FROM DAY 5 WED ONWARD SPREAD INCREASES DUE TO MULTIPLE UNCERTAINTIES... MOST PROMINENT BEING THE SHAPE OF THE UPSTREAM RIDGE BUILDING INTO WRN CANADA AND THE EMERGING POTENTIAL FOR SOME LEVEL OF UNDERCUTTING FLOW TO THE S. THE 12Z/18Z GEFS AND 12Z ECMWF MEANS WERE VERY CLOSE IN TRACKING THE NWRN UPR LOW INTO THE GRTBASIN... BY WAY OF THE ECMWF MEANS TRENDING SOMEWHAT MORE TOWARD THE GEFS SCENARIO OVER THE PAST 1-2 DAYS. THE 12Z CANADIAN ENSEMBLE MEAN FOLLOWS FROM ITS PRIOR RUN THAT SHOWED A MUCH MORE OPEN TROUGH EVOLUTION. THE MORE WRN/SWRN UPR LOW TRACK OF THE 12Z ECMWF IS IN THE MINORITY BUT WITHIN THE FULL GUIDANCE SPREAD. RECENT 12-HRLY RUNS FROM BOTH THE GFS AND ECMWF HIGHLIGHT THE VARIOUS POSSIBILITIES FOR WRN-CNTRL CONUS ENERGY IN RESPONSE TO THE SHAPE OF THE UPSTREAM RIDGE THAT MAY RANGE FROM BEING N-S ORIENTED TO A CLOSED HIGH OVER/NEAR BC. UNCERTAIN DETAILS ALOFT WILL BE KEY IN DETERMINING WHETHER ANY SIGNIFICANT DEVELOPMENT OCCURS FROM WAVINESS ALONG THE COLD FRONT PUSHING SEWD INTO THE PLAINS/MS VLY/UPR GRTLKS. ENSEMBLE MEAN CONTINUITY AND LOWER CONFIDENCE IN THE 12Z ECMWF AFTER TUE LEAD TO PRIMARY EMPHASIS ON THE 18Z GEFS/12Z ECMWF MEANS FOR DAYS 5-7 WED-FRI. THE 18Z GFS REMAINED CLOSE ENOUGH TO THIS SOLN TO ALLOW FOR 20-30 PCT WEIGHTING IN THE BLEND TO ADD A LITTLE DETAIL. ...SENSIBLE WEATHER HIGHLIGHTS... EXPECT MUCH COLDER AIR TO PUSH INTO WEST AND PLAINS FROM LATE TUE ONWARD WITH A BROAD AREA SEEING HIGHS OF 10-25F BELOW NORMAL FOR ONE OR MORE DAYS. THE MOST EXTREME READINGS SHOULD BE OVER THE ROCKIES/HIGH PLAINS. TEMPS MAY NOT THREATEN DAILY RECORDS BUT WILL STILL FEEL QUITE COLD GIVEN THE ROCKIES/PLAINS HAVE AVERAGED ABOVE NORMAL FOR THE MONTH THUS FAR. SNOW LEVELS WILL DECLINE CONSIDERABLY WITHIN THE PCPN SHIELD SPREADING ACROSS THE WEST WITH SNOW ALSO EXTENDING ACROSS THE NRN PLAINS. AS THE LEADING COLD FRONT BEGINS TO INTERACT WITH GULF MSTR... WARM SECTOR RNFL SHOULD INCREASE IN COVERAGE/INTENSITY BY THE LATTER HALF OF THE WEEK WHILE SUFFICIENTLY COLD LOCATIONS FROM THE CNTRL HIGH PLAINS NEWD MAY SEE SNOW AND/OR OTHER WINTRY PCPN. ERN STATES SHOULD BE RELATIVELY DRY THROUGH THE PERIOD ASIDE FROM LGT SNOW IN THE UPR/ERN GRTLKS EARLY IN THE WEEK. TEMPS WILL BE WELL BELOW NORMAL TO START THE WEEK BUT THEN REBOUND TO AND ABOVE NORMAL. RAUSCH