MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1201 PM EST SUN DEC 06 2015 VALID DEC 06/1200 UTC THRU DEC 10/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z EVALUATION INCLUDING MODEL PREFERENCE AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CLOSED LOW TRACKING ACROSS THE OHIO VALLEY MON AND EXITING INTO THE WRN ATLANTIC FOR TUE DEVELOPING SURFACE LOW IN THE WRN ATLANTIC BY TUE MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/GFS AND *04/12Z* ECMWF CONFIDENCE: SLIGHTLY BELOW AVERAGE MODELS AND ENSEMBLE MEANS CONTINUE TO BE IN FAIRLY SOLID AGREEMENT WITH THE LOW TRACKING ACROSS THE OHIO VALLEY BUT BEGINNING TO SPREAD AS THE WAVE SHIFTS OFF SHORE AND SURFACE CYCLOGENSIS OCCURS. THE 00Z ENSEMBLE SURFACE CLUSTER CONTINUED TO TIGHTEN SURROUNDING THE 00Z GFS/ECMWF...SO IT WAS SURPRISING TO SEE THE 06Z GFS AND 06Z GEFS SHIFT NORTH BY 2-3 DEGREES OF LATITUDE...NEAR THE LESS FAVORED 00Z UKMET THOUGH A BIT SLOWER (AS TO BE EXPECTED GIVEN UKMET'S FAST BIAS). THE NAM HAS GENERALLY BEEN WEAKER WITH THE SURFACE LOW AND WELL SOUTH OF THE BEST CLUSTER...HOWEVER THE 12Z RESOLVES SOME OF THE INTENSITY DIFFERENCES AND SHIFTED NORTH NEAR THE ENSEMBLE CLUSTER BUT ON THE NORTHERN AND FASTER PACE COMPARATIVELY...LOOKING SIMILAR TO THE *05/12Z* ECMWF. THE 12Z GFS APPEARS TO FOLLOW THE 06Z GEFS STEP BY STEP. THE 00Z ECMWF/CMC REMAIN TIGHT WITHIN THE 00Z ENSEMBLE AS EXPECTED THE UPSTREAM SHORTWAVE HAVING A SIGNIFICANT ROLE WITH THE EVOLUTION OF THE SPEED/DEPTH OF THE SHORTWAVE AND COASTAL CYCLOGENESIS...AND WITH RUN-TO-RUN INCONSISTENCIES WITH THIS WAVE...INCREASES SPREAD AND REDUCES CONFIDENCE. IF THIS WAVE IS WEAKER/SHIFTS NORTH LIKE THE 12Z GFS/NAM/UKMET THE SOLUTION WILL SHIFT TOWARD THE NORTH VS. THE DEEPER/SOUTHERN TRACK OF THIS WAVE. WITH THE FORECAST TEETERING BETWEEN THESE CAMPS...THE ENSEMBLES SHIFTING FROM DEEPER TO SHALLOWER AND THE 12Z RUNS HAVE STARTED TO HAVE BETTER DATA FROM THE WAVE BEING WITHIN THE RAOB NETWORK...WILL SHIFT TOWARD THE 12Z GFS/06Z GEFS...THOUGH NOT FULLY. WILL SUPPORT A BLEND OF THE 12Z NAM/GFS AND *04/12Z* ECMWF...ADDING THE 06Z GEFS TO THE BLEND WOULD ONLY DOUBLE DOWN ON THE GFS SOLUTION. CONFIDENCE IS SHAKEN BY THIS SHIFT...AS SUCH IS NOW AVERAGE OR SLIGHTLY BELOW AVERAGE AND WOULD BE BOLSTERED BY ANY OR BULK OF THE 12Z UKMET/CMC/ECMWF SHIFTING NORTH. SHORTWAVE ALONG THE NORTHWEST COAST THIS MORNING AND REACHING THE PLAINS ON MON AND SHEARS OUT ACROSS NEW ENGLAND BY WED COMPACT MID-LEVEL SHORTWAVE AND SURFACE LOW APPROACHING VANCOUVER ISLAND TONIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM/00Z ECMWF BLEND CONFIDENCE: BELOW AVERAGE AS NOTED IN PARAGRAPH TWO OF SECTION ABOVE...CONTINUITY CONTINUES TO BE DISHARMONIOUS WITH RESOLVING THE WAVE COMING ASHORE INTO THE OR COAST ATTM. THE TWO CAMPS ARE SET BY EVOLUTIONARY DIFFERENCES... THE 12Z NAM/GFS/00Z UKMET ARE GENERALLY NORTH AND SHALLOWER FOLLOWING A TREND SEEN IN THE LAST FEW ENSEMBLE SPAGHETTI DIAGRAMS...WHILE THE 00Z CMC/ECMWF ARE SOUTH AND A BIT STRONGER/CONSOLIDATED. ADDITIONALLY THE POTENTIAL INTERACTION OF THIS SHORTWAVE WITH WEAKER WAVES TO ITS NORTH...AS IT CROSSES THE ROCKIES...INFLUENCES HOW THE EVOLUTION OF THE MID-LEVEL PATTERN WILL TAKE PLACE. THE 12Z GFS/NAM TAKE THE NEXT COMPACT SHORTWAVE APPROACHING VANCOUVER ISLAND TONIGHT AND DRAW IT CLOSER TO THIS WAVE AND LEAD TO SOME BINARY INTERACTION DRAWING THE WAVE NORTH WHILE SHEARING IT AND FLATTENING THE FLOW ACROSS THE EASTERN GREAT LAKES/E ONTARIO BY TUES. NIGHT. THIS IS SUPPORTED BY THE 06Z GEFS AND TO A POINT THE 00Z ECENS MEAN (BEING FLATTER). THE 00Z ECMWF AND EVEN MORE SO THE 00Z CMC SHOW LESS INTERACTION WHICH ALLOWS THE WAVE TO REMAIN ON A SOUTHERN TRACK AND CONSOLIDATED A BIT LONGER OVER THE EASTERN GREAT LAKES. GIVEN THE BETTER ENSEMBLE MEAN SUPPORT AND NEWER DATA SURROUNDING THE WAVE IN A MORE DENSE DATA NETWORK SEEN WITH THE 12Z RUNS...WILL TIP THE HAND SLIGHTLY TO A 12Z NAM/GFS BLEND REPRESENTING THE 00Z ECENS/06Z GEFS MEANS AS BEST AS POSSIBLE. NEEDLESS TO SAY CONFIDENCE IS WELL BELOW AVERAGE WITH THIS WAVE AND ITS UPSTREAM COMPACT S/W NEARING THE PAC NW. HOPEFULLY THE 12Z UKMET/CMC/ECMWF WILL SUPPORT THIS SCENARIO TO ADD SOME CONFIDENCE. LOW AMPLITUDE SHORTWAVE REACHING WASHINGTON/OREGON MON NIGHT...AMPLIFYING INTO THE NORTHERN PLAINS TUE NIGHT AND BOTTOMING OUT OVER THE UPPER OHIO VALLEY BY WED NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 06Z GEFS CONFIDENCE: BELOW AVERAGE THE PLACEMENT AND TIMING OF THE WAVE APPEARS WELL HANDLED WITH THE WAVE APPROACHING THE COAST BY MONDAY NIGHT EXCEPT FOR THE 00Z CMC WHICH HAD A VERY DIFFERENT ORIENTATION. BY TUESDAY THE 12Z NAM IS STRONG BUT REMAINS FURTHER NORTH WITH INCREASING WAVE COMPRESSION EAST TO WEST BY THE END OF THE PERIOD WITHOUT DIGGING OUT THE TROF... WHICH DOES NOT SEEM TOO REALISTIC. THE 00Z UKMET/ECMWF AND 12Z GFS WERE MORE IN LINE WITH EACH OTHER DIGGING ACROSS THE NORTHERN PLAINS/NORTHERN MIDWEST. THE 00Z UKMET TYPICAL OF ITS BIAS WAS FAST BUT THE 12Z GFS TRENDED FASTER ALMOST IN LINE WITH THE 00Z UKMET. THE 00Z ECMWF WAS DEEPER AND PREFERRED EARLIER...AND IS IN PHASE IN TIMING WITH THE 00Z ECENS MEAN THOUGH THE MEANS GENERALLY AVERAGE OUT THE DEPTH OF THE TROF. THE 06Z GEFS SHOWED THIS SHIFT EASTWARD OF THE 00Z ECENS MEAN AND ECMWF OPERATIONAL BUT ALSO NOT AS FAST AS THE 00Z UKMET AND 12Z GFS. AS SUCH WILL SPLIT THE DIFFERENCE TO PREFER THE 06Z GEFS AT BELOW AVERAGE CONFIDENCE. STRONG GULF OF ALASKA CLOSED LOW WITH STRONG ZONAL FLOW AND EMBEDDED JET STREAKS/SHORTWAVES MOVING INTO PACIFIC NORTHWEST THROUGH WED NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND...FAVORING 00ECMWF/CMC/UKMET CONFIDENCE: SLIGHTLY BELOW AVERAGE THE MODELS ARE BROADLY SIMILAR HERE BY WED MORNING...BUT TIMING/AMPLITUDE DIFFERENCES REMAIN WITH SHORTWAVES EMBEDDED WITHIN TIGHTLY PACKED MID-LEVEL HEIGHTS. BY THE END OF DAY 3 ALL MODELS DEVELOP A STRONG WAVE WITH DEEP SURFACE REFLECTION BETWEEN 130-140W...THE 12Z GFS IS A BIT FASTER THE 12Z NAM IS A BIT SOUTH OF THE OTHERWISE TIGHTLY PACKED 00Z UKMET/CMC/ECMWF...FOR DAY 3. AT THIS POINT CONFIDENCE IS ACTUALLY HIGHER THAN NORMAL FOR SUCH A VOLATILE/FAST PACIFIC FLOW...BUT RUN-TO-RUN CONSISTENCY REMAINS GENERALLY LOW...AND WITH OVERALL GENERAL AGREEMENT IN THE MODELS...WILL RETAIN AN OPERATIONAL MODEL BLEND FAVORING THE TIGHTER PACKING OF THE 00Z ECMWF/CMC/UKMET...STILL SPREAD REMAINS LARGE ENOUGH FOR SLIGHTLY BELOW AVERAGE CONFIDENCE OVERALL. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA