MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 235 AM EDT SUN APR 17 2016 VALID APR 17/0000 UTC THRU APR 20/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ TROUGH/FRONT MOVING INTO THE NORTHEAST ON LATE MON/TUES...SURFACE CYCLOGENESIS OFF SE NEW ENGLAND TUESDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE ENSEMBLE SPAGHETTI PLOTS CLEARLY SHOW THE 12Z UKMET IS FAIRLY OUT OF PHASE WITH THE GUIDANCE. STILL THE REST OF THE SUITE THERE REMAINS FAIRLY HIGH SPREAD WITH THE 12Z ECMWF AND MANY ECENS MEMBERS FAVORING A SLIGHTLY SLOWER/DEEPER AND SOUTHERLY TRACK OF THE FORCING AND EVENTUAL SURFACE CYCLOGENESIS OFF THE SE NEW ENGLAND COAST TUESDAY. THE 12Z CMC IS NEXT CLOSEST TO SUPPORT THIS SOLUTION. THIS COUNTER TO THE 00Z NAM/GFS WHICH TRACK MORE NORTHERLY THROUGH N VT/NH...STILL THE TIMING OF THE TROF OVERALL REMAINS STRONG ENOUGH TO CONTINUE A NON-UKMET BLEND BUT GIVEN THE DIFFERENCES REMAINING ON THE TRACK/EVOLUTION...CONFIDENCE IN THIS BLEND IS AVERAGE. 07Z UPDATE: ISSUES WITH THE UKMET HAVE SEEMED TO RESOLVE WITH RESPECT TO THE TIMING OF THE WAVE OVERALL. HOWEVER THE NON-NCEP OPERATIONAL ARE A BIT MORE AMPLIFIED (SEE 7H) AND THE 00Z CMC REMAINS ON THE SOUTHERN SIDE OF THE SURFACE LOW CLUSTER. HOWEVER GIVEN THE OVERALL AGREEMENT WILL SUPPORT AN OPERATIONAL MODEL BLEND WITH SOME INCREASED CONFIDENCE TO SLIGHTLY ABOVE AVERAGE. INTERMOUNTAIN WEST/PLAINS TROUGH AND CUTOFF UPPER LOW ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-NAM BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE OVERALL THERE IS CONTINUES TO BE FAIRLY STRONG AGREEMENT IN THE OVERALL PATTERN WITH THE CLOSED LOW AND ITS EVOLUTION...SMALL DIFFERENCES IN PLACEMENT/TIMING OF THE INTERNAL SHORTWAVES OBVIOUSLY PLAY KEY ROLES IN THE DIFFERENCES. THE 12Z ECMWF REMAINS ON THE SOUTHERN SIDE OF THE GUIDANCE AND IS SUPPORTED BY THE 12Z CMC BUT THE 12Z CMC OVERALL SEEMS TO HAVE THE MOST DISTINCT DIFFERENCES OVERALL WITH A DEEPER SLOWER/SOUTHERN LOBE ON TUESDAY INTO WED MAKING IT A BIT LESS RELIABLE. THE 00Z NAM HAS TRENDED A BIT SOUTH OF ITS NORTHERN POSITION AND TRENDS CLOSER TOWARD THE GFS/GEFS POSITIONS. THE 00Z GFS ALSO SHIFTED SOUTH AND SLIGHTLY EAST HAVING A SIMILAR PLACEMENT AS THE 12Z ECENS MEAN...BRINGING ADDITIONAL CONFIDENCE IN A GFS/ECMWF SOLUTION. THE 12Z UKMET ALSO APPEARS TO BE A NICE MIDDLE GROUND SOLUTION THROUGH MUCH OF THE EVOLUTION OF THE UPPER LOW AND SURFACE TROF...HOWEVER A MUCH DEEPER/TIGHTER GRADIENT FROM A DEEPENING NORTHERN STREAM WAVE ON WED IS PAUSE FOR SOME CONCERN BUT SEEMS MINIMAL ATTM THROUGH DAY 3 TO KEEP IN WITHIN THE PREFERRED BLEND. ALL CONSIDERED A PREFERENCE FOR A NON-CMC BLEND IS PREFERRED THOUGH FAVORING THE 00Z GFS SOLUTION WITHIN THE WEIGHTING. AS THE SPREAD IS GENERALLY SMALL...CONFIDENCE REMAINS SLIGHTLY ABOVE AVERAGE IN THE OVERALL MASS FIELDS. QPF DIFFERENCES ARE DRIVEN BY THE SMALLER SCALE INTERACTIONS WITH THE EMBEDDED SHORTWAVES...AS SUCH PLEASE REFER TO QPFPFD FOR ADDITIONAL DETAILS. 07Z UPDATE: 00Z NON-NCEP MODELS CONTINUE TO CONSOLIDATE AND SHIFT TOWARD THE 12Z ECENS WHICH WAS MATCHED BY THE 00Z GFS. THOUGH THE NAM WAS ON THE RIGHT TREND...THESE TRENDS TOWARD THE SOUTH PLACE THE NAM ON THE OUTSIDE ON THE NORTH SIDE OF THE GUIDANCE AND MOST OUT OF PHASE...AS SUCH WILL SUPPORT A NON-NAM BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. UPPER LOW ENTERING CENTRAL WEST COAST BY WED MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: AVERAGE AN CUT-OFF UPPER LOW WILL MOVE TOWARD THE CA COAST BY TUES...GENERALLY WEAKENING AND OPENING UP BY LANDFALL WED MORNING. WPC HAS BEEN FAVORING A SLOWER PROGRESS OF THE UPPER LOW GIVEN THE BLOCK DOMINATING THE CENTRAL U.S...THIS TREND CONTINUES WITHIN THE ENSEMBLE SUITE THE 18Z GEFS/12Z ECENS MEAN...HOWEVER THE 12Z IS CLEAR OUTLIER BEING FASTER AND QUICKER TO WEAKEN EVEN OUTPACING THE 12Z CMCE THOUGH THAT IS FURTHER EAST THAN THE MAIN CLUSTER. THE 00Z NAM ALSO SHIFTED A BIT FASTER CLOSER TOWARD THE 15/21Z SREF TIMING...THIS SEEMS TO AFFECT THE LOWER LEVELS PARTICULARLY THE SURFACE; THIS IS NOT AS DRAMATIC AS THE 00Z CMC BUT GIVEN THE REST OF THE GUIDANCE 00Z GFS/12Z ECMWF/UKMET ARE BETTER ALIGNED WITH THE ENSEMBLE MEANS...AS SUCH WILL FAVOR A 00Z GFS AND 12Z ECMWF/UKMET BLEND AT AVERAGE CONFIDENCE. 07Z UPDATE: THE 00Z ECMWF TRENDED A SHADE FASTER TOWARD THE NAM AND THE 00Z UKMET SUPPORTS THE GFS...THIS SPREAD IS VERY MINOR OVERALL. THE 00Z CMC MADE A DRAMATIC SHIFT FROM BEING THE FASTEST MODEL TOWARD THE COMPLETE OPPOSITE SIDE OF THE SCALE AND IS NOW THE SLOWEST AND FURTHEST SOUTH...THIS INCONSISTENCY AND DISAGREEMENT WITH AN OTHERWISE GOOD CLUSTER SUPPORTS A NON-CMC BLEND AT AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA