EXTENDED FORECAST DISCUSSION ...CORRECTION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 106 AM EST THU DEC 24 2015 VALID 12Z SUN DEC 27 2015 - 12Z THU DEC 31 2015 ...EXCESSIVE RAIN THREAT FROM THE S-CENTRAL US TO MID-LOWER MS/OH VALLEYS... ...HEAVY SNOWFALL SCENARIO FOR THE SOUTHERN PLAINS... ...MODEL PREFERENCES... THE PATTERN HAS JUST ENOUGH FAST-MOVING ENERGY MIGRATING ACROSS THE LOWER 48 AND A SWIFT POLAR JET OVER ARCTIC CANADA INVOF 55 NORTH LATITUDE ---TO KEEP SOME OF THE DETAILS OUT OF THE MEDIUM RANGE DAYS 6-7. I DID LIKE THE MID-LEVEL DETAIL OF THE DETERMINISTIC 23/12Z ECMWF IN THREE KEY AREAS OF THE LOWER 48---ENOUGH SO TO USE ABOUT 20% OF IT---TO HELP WITH SOME OF THE DETAIL. USING AN ENSEMBLE MEAN APPROACH WOULD CERTAINLY 'WASH OUT' MUCH OF THE DETAIL IN THE WEST AND PLAINS---BUT EVEN THE ECMWF IS NOT A COMPLETELY PERFECT PROG SOLUTION OVER SOUTH CENTRAL CANADA AFTER DAY 6 --- SO ITS ECENS MEAN SHOULD HOLD THE PATTERN (50%) ALONG WITH THE NAEFS (30%) THROUGH DAY 7. INCLUDED THE NAEFS TO HANDLE THE DAY4-5 WINTER CYCLONE EXITING SOUTHEAST CANADA---THOUGH THE 23/12Z GEFS MEAN SEEMS A MUCH BETTER FIT WEST OF THE MISSISSIPPI AT/BEYOND DAY 5. IF I THOUGHT A STRAIGHT 100% MODEL WOULD BE ABLE TO PINPOINT EVERY DETAIL--- I WOULD USE IT. BUT FIGURED THE GFS/ECMWF DETERMINISTIC APPROACH HEADING INTO THE 29/12Z TIME FRAME (DAY5) WILL KEEP THE FORECAST IN DECENT SHAPE OUT WEST---WHERE THE MORE ACTIVE WEATHER IS ANTICIPATED. BUT BELIEVE USING TOO MUCH OF THE GFS AT DAY 5 ---UNFORTUNATELY EMPHASIZES A LITTLE TOO MUCH 'COOL DOWN' ACROSS THE NORTHEAST. ...UNCERTAINTY ASSESSMENT... THE FOCUS IN THE MEDIUM RANGE TONIGHT WAS TO LOOK 'BEYOND' THE WELL-ADVERTISED DAY4-5 WINTER CYCLONE MIGRATING FROM THE OZARKS TO THE GREAT LAKES. AND THE 3 KEY AREAS LEFT IN ITS WAKE---SEEM JUST AS IMPORTANT. FIRST...THE OUTCOME OF THE SOUTHEAST RIDGE. FIND IT HARD TO IMAGINE A 582 DM CONTOUR (A VALUE THAT MARKS ITS 'PERIPHERY') WILL BE ERODED OVER THE NORTHEAST---LIKE THE GFS ATTEMPTS TO ACCOMPLISH ON MONDAY. WHICH IS WHY IT IS HARD TO USE ITS DETERMINISTIC RUN BEYOND 29/12Z. THE GEFS IS THE JUST AS 'TROUGHY'. SEEMS LIKE THE PATTERN LATELY HAS BEEN TO GENERATE BETTER ENERGY FURTHER DOWNSTREAM OVER ATLANTIC CANADA. THE FACT THAT THE 23/12Z RUN OF THE GFS IS FASTER THAN THE 23/12Z ECMWF --- WITH THE FOUR CORNERS LOW (DAYS 3-4) AND ITS ENERGY TRANSITING THE GREAT LAKES---TENDS TO ERODE ITS SOLUTION DOWNSTREAM (AS A STRONGER WAVE) OVER THE GULF OF MAINE. UNTIL THEN...COULD NOT FIND ANYTHING REALLY WRONG WITH THE GFS --- AND ITS TRACK SOLUTION OVER THE CENTRAL PLAINS/MIDWEST AND GREAT LAKES (OUR DAY4-5 WINTER CYCLONE). IT IS A DRIER SOLUTION ALONG THE NORTHWEST PERIPHERY OF THE DAY 3 THROUGH 5 PERIOD---BUT HAS NOT WAVERED WHATSOEVER WITH THE LONG-DURATION WINDS FUNNELING IN BEHIND THE LOW-LEVEL CYCLONE. CYCLONE TRACK IS VERY REASONABLE JUST A TAD TOO FAST. WILL ASSUME THAT THE LOCAL NWS OFFICES ALONG THE STORM TRACK--- HAVE A BETTER FOCUS/HANDLE ON WHAT THE GFS FAVORS VERSUS THE ECMWF CONCERNING IMPACTS INSIDE OF THE 48 HOUR POINT. WILL AT LEAST OFFER SOME OPTIONS HERE. THE SECOND REGION OF THE COUNTRY --- AND WHERE THE ECENS/ECMWF SEEMS TO 'SHINE' IS OVER THE FOUR CORNERS---AND A 'FOLLOW-UP' SHORTWAVE EMBEDDED IN THE PACIFIC TROUGH FOR DAY 5-6. THE DETERMINISTIC GFS ACTUALLY LOOKS BETTER TONIGHT (ITS 23/12Z RUN AND 23/18Z RUN). AND IF IT WASN'T SO FAST AND EAST (OVER QUEBEC) WITH THE DAY4-5 WINTER CYCLONE --- IT MIGHT BE WORTH USING TO DEPICT THE MID-LEVEL STRUCTURE OF THE 'FOLLOW-UP' WAVE EXITING THE SOUTHERN HIGH PLAINS AROUND 30/00Z. THE 23/12Z CANADIAN IS WAY TOO SLOW AND TOO SEPARATED BY 30/00Z BETWEEN WYOMING AND ARIZONA TO BE OF MUCH USE. UNFORTUNATELY...THE NATIONAL BLEND DID NOT OFFER MUCH IN THE WAY OF 'HIGHER' POPS---WHEN IT SEEMS THE SYSTEM IS 'REAL'---BUT THE 12Z GUIDANCE THINKS IT WILL BE A MOISTURE-STARVED SYSTEM. AND LAST BUT NOT LEAST---THE THIRD WAVE IN THIS SEQUENCE...MOVING ACROSS THE WEST COAST. THE ECMWF IS NOT PERFECT---BUT LOOKS MUCH LIKE ITS ECENS MEAN AND MAINTAINS A 'COMPACT-NESS' THAT SEEMS TO FIT WHAT WE HAVE SEEN IN THE DECEMBER FLOW PATTERN (THIS PARTICULAR EL NINO SCENARIO)---A CONCENTRATED PRECIPITATION MAKER AND LAST OF THE 'TRACK-ABLE' SHORTWAVES IDENTIFIED YESTERDAY. HERE AGAIN, THE MID-LEVEL SYSTEM APPEARS TOO WEAK TO BECOME A SURFACE REFLECTION --- ONLY A SUB-1024 MB LOW OFF THE CALIFORNIA COAST. ...SENSIBLE WEATHER HIGHLIGHTS... SNOW AND WINDY CONDITIONS WILL BE PREVAILING CONDITIONS ACROSS THE SOUTHERN HIGH PLAINS WITH A SUNDAY-MONDAY CYCLONE TRACKING NORTHEASTWARD INTO THE GREAT LAKES. THE SURFACE TRACK MIGRATES NORTHWARD INTO THE MIDWEST/GREAT LAKES ON TUESDAY---THEN BEGINS TO SHEAR OUT AS IT COMES INTO THE FAST-MOVING CONFLUENT WESTERLY FLOW ACROSS EAST CENTRAL CANADA. EXTREME RAINFALL IS ANTICIPATED ALONG AND AHEAD OF THIS CYCLONE---AND AGREE WITH OUR PREVIOUS WPC (DAY4-5 QPF) ON THE DISTRIBUTIONS AND AMOUNTS. IT HAS BEEN A SIGNAL FOR SEVERAL DAYS NOW...OVER EASTERN OKLAHOMA AND THE OZARKS. THE SOUTHWEST FLOW PATTERN ALOFT AND PACIFIC TROUGH WILL CONTAIN TWO MORE SHORTWAVES---ALL HAVING THE POTENTIAL TO PRODUCE PRECIPITATION AND SNOWFALL ACROSS THE WEST (SIERRA)...SOUTHERN GREAT BASIN...FOUR CORNERS AND SOUTH CENTRAL PLAINS DURING THE LATTER HALF OF THIS MEDIUM RANGE PERIOD. LAST BUT NOT LEAST---A CONTINUED MILD PATTERN BUT WET PERIOD FOR THE SOUTHEAST WITH PERIODS OF WARM ADVECTION PRECIPITATION FOR THE NORTHEAST. VOJTESAK