EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 146 AM EST TUE NOV 24 2015 VALID 12Z FRI NOV 27 2015 - 12Z TUE DEC 01 2015 ...OVERVIEW... THE FCST MAINTAINS THE IDEA OF A PATTERN CONDUCIVE TO ACTIVE WEATHER OVER THE CENTRAL U.S. IN PARTICULAR WITH THANKSGIVING WEEKEND TRAVEL LIKELY TO BE AFFECTED BY VARIOUS WINTRY PCPN TYPES AND HVY RNFL DEPENDING ON LOCATION. ON A SMALLER SCALE SOME PCPN MAY BE PSBL TO THE W AND E OF THE DOMINANT WEATHER FOCUS. FROM THE GUIDANCE PERSPECTIVE... SOLNS CONTINUE TO DISPLAY MEANINGFUL SPREAD WITHIN AN EVOLUTION THAT SUGGESTS SOME DISLODGING OF AN INITIAL WRN NOAM REX BLOCK CONFIGURATION AS PROGRESSIVE BUT POTENTIALLY SPLIT ERN PAC FLOW HEADS TOWARD THE WEST COAST. ...GUIDANCE EVALUATION/PREFERENCES... FOR DAYS 3-5 FRI INTO SUN A MODEL/ENSEMBLE CONSENSUS APPROACH INCORPORATING THE 12Z ECMWF/18Z GFS AND 12Z ECMWF MEAN/GEFS MEAN... OPERATIONAL WEIGHTING GRADUALLY DECREASING WITH TIME... PROVIDED A GOOD INTERMEDIATE SOLN. THERE IS STILL UNCERTAINTY OVER HOW MULTIPLE PIECES OF ENERGY WILL EVOLVE WITHIN THE OVERALL WRN CONUS UPR LOW... LEADING TO DIFFS IN DEPTH/POSN OF THE FEATURE AT A PARTICULAR TIME. AT SOME FCST HRS THE 12Z ECMWF MEAN LEANS A BIT TO THE WEAKER SIDE OF THE GUIDANCE SPREAD. ACROSS THE EAST THERE CONTINUE TO BE SIGNIFICANT DIFFS WITH ERN NOAM TROUGH AMPLITUDE LEADING TO ISSUES WITH PCPN COVERAGE/LOCATION. UKMET RUNS HAVE TENDED TO BE AMPLIFIED EXTREMES WHILE IN VARIOUS WAYS GFS/ECMWF RUNS HAVE TENDED TO BE SOMEWHAT MORE AMPLIFIED THAN THE ENSEMBLE MEANS AS WELL. MULTI-DAY TRENDS HAVE BEEN LEANING TOWARD A LESS AMPLIFIED TROUGH CLOSER TO THE MEANS. THE 18Z GFS WAS A NOTABLE IMPROVEMENT OVER THE 12Z RUN BUT COMPARED TO NEW 00Z SOLNS THUS FAR THE SIMILAR 00Z GFS MAY STILL BE SOMEWHAT FAST AMPLIFIED WITH THE UPR TROUGH. SPREAD INCREASES BY DAYS 6-7 MON-TUE AS INCOMING PACIFIC FLOW MAY SERVE TO ACCELERATE THE WRN UPR LOW INTO THE CNTRL U.S.. HOWEVER MDLS/ENSEMBLES DIFFER GREATLY IN WHAT THIS INCOMING PAC FLOW WILL LOOK LIKE AND THE TIMING/EVOLUTION OF THE EJECTING UPR LOW ENERGY. THE ONE POINT OF RELATIVE AGREEMENT IS TOWARD A SPLIT FLOW PATTERN NEAR THE WEST COAST WITH SOMEWHAT LESS PRONOUNCED RIDGING THAN SEEN IN THE PAST COUPLE ECMWF RUNS. DOWNSTREAM CONTINUE TO PREFER LEANING AWAY FROM THE FASTER UPR LOW SOLNS SUCH AS SOME GFS RUNS AND THE OLD 00Z/23 ECMWF... GIVEN THE BLOCKY NATURE OF THE WRN NOAM PATTERN INTO SUN. IN ADDITION GFS RUNS COULD BE OVER-DEVELOPING THE SFC SYSTEM IN THE COLD AIR. PAST COUPLE CMC RUNS HAVE ALSO BEEN FAIRLY DEEP WITH THE UPR LOW OVER THE CNTRL U.S. BUT MUCH MORE MUTED THAN GFS RUNS AT THE SFC. THIS PART OF THE FCST EMPHASIZES THE 12Z GEFS/ECMWF MEANS... INCLUDING ONLY 20 PCT OF THE 12Z ECMWF TO BALANCE ITS LESS CONFIDENT FCST NEAR THE WEST COAST VERSUS A MORE DESIRABLE SLOWER UPR LOW TIMING FARTHER EWD. ...SENSIBLE WEATHER HIGHLIGHTS... THE AREA ENCOMPASSING THE SRN PLAINS NEWD INTO PARTS OF THE TN VLY/LOWER OH VLY CONTINUES TO SHOW BEST POTENTIAL FOR PERIODS OF HVY RNFL FROM LATE THIS WEEK THROUGH THE WEEKEND. CONSULT LATEST NHC PRODUCTS FOR FURTHER INFO ON ERN PAC T.D. TWENTY-TWO-E WHICH IS CURRENTLY FCST TO STRENGTHEN AND ULTIMATELY MAY PROVIDE EXTRA MSTR TO ENHANCE THE SRN PLAINS ACTIVITY. TO THE NW OF THE HVY RAIN AREA EXPECT SOME WINTRY PCPN TO EXTEND ACROSS THE NRN HALF OF THE PLAINS AS THE WRN UPR LOW FINALLY EJECTS EWD. BY THE LATTER HALF OF THE PERIOD THERE IS STILL CONSIDERABLE UNCERTAINTY IN COVERAGE/TIMING OF BOTH NRN TIER WINTRY PCPN AS WELL AS ERN CONUS RNFL. THE FIRST HALF OF THE PERIOD MAY BRING SOME LGT/SCT PCPN TO CA. THEREAFTER EXPECT A GENERAL INCREASE IN MSTR ALONG THE CNTRL-NRN WEST COAST BUT WITH SIGNIFICANT QUESTION MARKS REMAINING AS TO THE TIMING/EXTENT OF THIS TREND. WITHIN THE INITIALLY VERY COLD PATTERN OVER THE WRN-CNTRL STATES... THE MOST EXTREME TEMPS SHOULD BE 10-25F BELOW NORMAL FOR HIGHS OVER AND JUST E OF THE ERN SLOPES OF THE CNTRL-SRN ROCKIES FRI-SAT. A BROAD AREA OF MINUS 5-15F ANOMALIES SHOULD LINGER ACROSS THE SRN TIER INTO EARLY NEXT WEEK WHILE THE NRN PLAINS AND VICINITY SHOULD SEE TEMPS TREND ABOVE NORMAL. ACROSS THE EAST WARM TEMPS ON FRI WILL BE REPLACED BY NEAR TO SLIGHTLY BELOW NORMAL READINGS. RAUSCH