MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1242 PM EDT WED OCT 26 2016 VALID OCT 26/1200 UTC THRU OCT 30/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z GUIDANCE EVALUATION INCLUDING MODEL PREFERENCE AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ LARGE SCALE UPPER LEVEL TROUGH OVER THE NORTHEAST U.S. THROUGH THURSDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE LONGWAVE UPPER LEVEL TROUGH AXIS IS EXPECTED TO HOLD BACK ACROSS THE NORTHEAST THROUGH THURSDAY WITH FAIRLY STRONG/PERSISTENT SURFACE HIGH BLOCKING APPROACHING SURFACE WAVE. MODELS CONTINUE TO SHOW STRONG ALIGNMENT WITH ONLY THE CMC SHOWING A SLIGHTLY FASTER DECAY THAN THE REST OF THE SUITE; GENERALLY MINOR IN THE GRAND SENSE. AS SUCH A GENERAL MODEL BLEND IS PREFERRED AT ABOVE AVERAGE CONFIDENCE. LOW PRESSURE SYSTEM TRACKING FROM THE CENTRAL PLAINS TO THE EAST COAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/NAM AND 00Z ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE SHORTWAVE IN SASKATCHEWAN AND WAVE ENTERING THE GREAT LAKES CURRENTLY ALONG WITH THE PERSISTENT BLOCK/LONGWAVE TROF OVER NEW ENGLAND WILL ALLOW FOR A CONSOLIDATION OF THE WAVE ACROSS THE EASTERN GREAT LAKES BY EARLY FRIDAY. GOOD AGREEMENT IN TIMING/STRENGTH/POSITION EXISTS WITH THE SURFACE WAVE THROUGH THE GREAT LAKES WITH EVENTUAL TRANSITION TOWARD THE COAST/LONG ISLAND FRIDAY MORNING. AFTERWARD MODEL DIFFERENCES START TO UNFOLD WITH THE 00Z UKMET STALLING/DEEPENING OVER THE GULF OF MAINE UNDER INFLUENCE OF FASTER DEEPENING UPSTREAM SHORTWAVE THAT SEEMS A BIT TOO AGGRESSIVE COMPARED TO OTHER GUIDANCE. THE 00Z ECMWF SHOWS SOME HINT OF A SLOWER/WOBBLE LIKE THE UKMET IN LINE WITH ITS DEEPER/SLOWER BIAS COMPARED TO SAY THE FASTER 12Z GFS/NAM BUT REMAINS PROGRESSIVE ENOUGH THAT A TYPICAL WEIGHTED BLEND WITH THE GFS SHOULD RESULT IN A MORE FAVORABLE OUTCOME TOWARD REALITY. THE 00Z CMC WHILE IN LINE WITH TIMING OF THE TROF AND SURFACE LOW...IT APPEARS A BIT SHALLOW AND ELONGATED LATITUDINALLY TO FIT WITH THE PREFERENCE. BY THE END OF DAY 3...THE GFS/GEFS/NAM ARE A BIT FASTER THAN THE 00Z ECMWF TYPICAL OF TRADITIONAL DAY 3 SPREAD. ALL CONSIDERED A 12Z GFS/NAM WITH 00Z ECMWF BLEND IS PREFERRED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. WEAKENING UPPER LEVEL TROF OFF WEST COAST SHIFTING ENERGY ACROSS THE NORTHERN TIER FRI NEARING NEW ENGLAND SAT WITH ASSOCIATED SURFACE LOW ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/06Z GEFS AND 00Z ECMWF BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE THE CYCLONIC GYRE ALOFT WITH NUMEROUS SMALLER SCALE EMBEDDED SHORTWAVES CONTINUES TO WEAKEN OVER THE OFFSHORE WATERS WEST OF THE PACIFIC NORTHWEST AND SHED ENERGY INTO THE WESTERN US RIDGE THURS/FRI. MODELS CONTINUE TO COME INTO BETTER AGREEMENT IN TIMING AND EVOLUTION OF THE SHORTWAVE CROSSING THE ROCKIES INTO THE NORTHERN TIER THOUGH THE 00Z UKMET CONTINUES TO REMAIN FASTER THAN THE REST OF THE GUIDANCE. THE 12Z GFS HAS SHOWN A SIZABLE SHIFT IN PLACEMENT OF THE SHORTWAVE AS WELL AS THE SURFACE REFLECTION ABOUT 150-200 KM SOUTH OF THE 00Z/06Z OPERATIONAL AND 06Z GEFS MEAN SOLUTION EVEN A BIT SOUTH OF THE ECWMF BUT IN MUCH BETTER PROXIMITY TO THE ECMWF/ECENS MEAN COMPARED TO THE NAM/UKMET/CMC/GEFS SOLUTIONS NORTH. AS THE WAVE AMPLIFIES ACROSS THE GREAT LAKES...TIMING/SHAPE AND PLACEMENT BECOME MUCH BETTER ALIGNED BEFORE THE 12Z GFS REMAINS SLOWER AND SOUTHWARD COMPARED TO THE REST OF THE GUIDANCE CROSSING INTO NEW ENGLAND. A BLEND OF THE 12Z NAM AND 06Z GEFS ALONG WITH THE 00Z ECMWF (REPRESENTING THE 00Z ECENS MEAN) SEEMS LIKE A GOOD MIDDLE GROUND COMPROMISE. CONFIDENCE REMAINS SLIGHTLY BELOW AVERAGE GIVEN THE REMAINING SPREAD OF TWO CAMPS THOUGH THE NORTHERN TIER EVEN AS CONSENSUS GETS A BIT BETTER CROSSING THE GREAT LAKES. LOW PRESSURE SYSTEM APPROACHING THE CALIFORNIA COAST BY LATE WEEK WEAKENING THROUGH INTERMOUNTAIN WEST SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ PREFERENCE: 12Z NAM/GFS AND 00Z UKMET BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE POTENT SHORTWAVE THAT CLOSES OFF SHORTLY AT THE BASE OF THE WEAKENING TROF THAT HAS DOMINATED THE WEST COAST FOR THE LAST FEW DAYS CONTINUES TO TREND SLOWER WITH EACH NEW CYCLE. THE 00Z ECMWF WHICH HAD TRENDED SLOWER TOWARD BETTER CONSENSUS WITH THE 00Z CYCLE...WITH THE SHIFT OF THE 12Z GFS BACK WEST TOWARD THE NAM SOLUTIONS...CONTINUES TO BE FASTER MAKING LANDFALL IN CA BEFORE SHEARING ACROSS THE GREAT BASIN SATURDAY. THOUGH THE TREND IS FOR SLOWER...THE 00Z CMC CONTINUES TO BE WELL WEST OF THE OVERALL SPREAD EVEN MORE THAN THE ECMWF IS EAST. THE DEVOLUTION OF THE WAVE ACROSS THE GREAT BASIN IS HANDLED VERY SIMILARLY BY THE 00Z UKMET AND 12Z GFS/NAM TO HAVE SOME CONFIDENCE IN SUPPORTING THIS BLEND AT THIS TIME. GIVEN THE RUNS CONTINUE TO VARY CONFIDENCE IS NOT PARTICULARLY HIGH THAT THE BLEND HAS SETTLED ON A COMMON SOLUTION AND THEREFORE REMAINS SLIGHTLY BELOW AVERAGE. APPROACHING DEEP UPPER LOW OFF NORTHWEST COAST FRI/SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ PREFERENCE: 12Z NAM/GFS AND 00Z CMC BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE A DEEP TROF BEGINS TO EXPAND/DEVELOP SOUTH OF THE ALASKAN PENINSULA THURS MORNING WITH A LEAD SHORTWAVE ACTING AS A KICKER WAVE FROM THE DEVOLVING UPPER LOW NEAR THE WEST COAST BY LATE THURSDAY. THE IS ENCOURAGING GROWING CONSENSUS OF THE MAGNITUDE/TIMING OF THIS WAVE THROUGHOUT THE ENSEMBLE AND DETERMINISTIC GLOBAL GUIDANCE. AS THE UPPER LOW EXPANDS AND DROPS SOUTHWEST TOWARD THE NW COAST...A SECOND SHORTWAVE ROUNDS THE BASE AND SKIRTS THE WA/OR COAST LATE FRIDAY INTO EARLY SATURDAY. DIFFERENCES HERE ON CONSOLIDATION OF THE WAVE LEAD TO A DEEPER SURFACE REFLECTION BY THE 00Z UKMET FOLLOWED BY A SLIGHTLY WEAKER PRESENTATION IN THE 00Z CMC. THE 12Z NAM AND GFS BOTH TRENDED IN THIS DIRECTION AS WELL PROVIDING SOME CONFIDENCE IN THIS EVOLUTION. THIS ALSO LEADS TO A LARGER ELONGATION OF THE UPPER LOW PRESENTED BY THESE MODELS BUT ALSO AWAY FROM THE VAST MAJORITY OF THE ENSEMBLE MEMBERS PRODUCING SOME REDUCED CONFIDENCE IN THIS ASPECT. THE 00Z ECMWF/ECENS MEAN REMAIN A DEEPER MORE CONCENTRIC INNER CORE TO THE UPPER LOW MUCH LONGER THAN THE REST OF THE DETERMINISTIC GUIDANCE AND WHILE THE CMC DOES SHIFT SLOWER WITH THE BASE OF THE TROF TYPICAL OF ITS SLOWER BIAS IT IS MUCH WEAKER AND MORE ELONGATED FAVORING THE GFS/NAM SOLUTIONS. AS A COMPROMISE TOWARD CONTINUITY/ENSEMBLE SOLUTIONS AND THE SLIGHTLY FASTER/EASTWARD SHIFT OF THE 12Z GFS/NAM AND 00Z UKMET/CMC...WILL SUPPORT A 12Z GFS/NAM AND 00Z CMC BLEND. LARGE SCALE EVOLUTION SEEMS FAIRLY CONSISTENT WITH THE UPPER LOW BUT THE IMPORTANT WX DRIVING INTERNAL SHORTWAVE DIFFERENCES REMAIN TOO LARGE AT THIS TIME TO BE PARTICULARLY CONFIDENT IN THIS COMPROMISE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA