MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 242 AM EDT SAT MAR 19 2016 VALID MAR 19/0000 UTC THRU MAR 22/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z GUIDANCE EVALUATION INCLUDING MODEL PREFERENCES AND FORECAST CONFIDENCE UPPER LOW DIPPING DOWN THROUGH MAINE/SE CANADA SAT/EARLY SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE DETERMINISTIC MODELS ARE IN STRONG AGREEMENT WITH SOLID SUPPORT FROM THE ENSEMBLE MEANS TO SUPPORT AN OPERATIONAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE FOR THE UPPER LOW DESCENDING ACROSS THE GULF OF ST. LAWRENCE CLIPPING NE MAINE SAT AND EXITING BY SUN. DEVELOPING UPPER LOW ACROSS THE MIDWEST WHICH EVENTUALLY LEADS TO CYCLOGENESIS OFF THE CAROLINAS LIFTING JUST OFF SHORE OF NEW ENGLAND TOWARD NOVA SCOTIA SUN/MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECMWF/UKMET BLEND CONFIDENCE: AVERAGE MODELS CONTINUE TO INCH CLOSER INTO BETTER AGREEMENT. THE 12Z ECENS MEAN HAS REMAINED QUITE CONSISTENT THROUGHOUT THE EVOLUTION OF DEVELOPING COASTAL LOW WITH SLIGHT SHIFTS EASTWARD WITH TIME...AND FOR EVERY STEP EAST....THE GEFS/GFS SLOWS AND STEPS WEST TWICE TOWARD THE ECENS TRACK. BOTH THE 12Z ECENS MEAN AND 18Z GEFS ARE MORE CENTRAL THAN THEIR OPERATIONAL RUNS INDICATING SOME BETTER CONGRUENCE. THE 12Z ECMWF/UKMET REMAINS MOST CENTRAL TOWARD REPRESENTING THE 12Z ECENS MEAN...WHILE THE 12Z CMC IS NOW A SOUTHERN AND SLOWER OUTLIER WHICH IS QUITE EVIDENT IN THE SURFACE CLUSTER PLOT AS WELL AS THE ENSEMBLE SPAGHETTI DIAGRAMS; THIS IS A BIT SURPRISING CONSIDERING THE 12Z CMCE WAS VERY CLOSE TOWARD THE 12Z ECENS MEAN. THE 00Z NAM CONTINUES TO STRUGGLE WITH LARGE RUN TO RUN INCONSISTENCY; THE 18Z WAS FAST AND EAST OF THE GFS AND NOW THE 00Z IS INITIALLY SLOW LIKE THE 12Z CMC AND THEN LEADS TO A BROAD/DUAL CENTERED SURFACE REFLECTION THAT SEEMS OUTLANDISH BY ENSEMBLE STANDARDS. THE 00Z GFS CONTINUED ITS RUN TO RUN SLOWING OF THE TROF AS IT UNFOLDS/AMPLIFIES FURTHER SOUTH THAN IT HAS OVER THE PAST FEW DAYS. GIVEN THE 00Z GFS RUN REMAINS EAST AND STILL A BIT FAST INITIALLY WILL CONTINUE TO FAVOR A 12Z ECMWF/UKMET BLEND TO REPRESENT THE ECENS MEAN; CONFIDENCE REMAINS AVERAGE. 07Z UPDATE: THE 00Z ECMWF IS A BIT WEAKER OVERALL PARTICULARLY WITH THE LEADING SHEARED UPPER LEVEL ENERGY SWINGING THROUGH THE OHIO VALLEY INTO THE UPPER MID-ATLANTIC SAT NIGHT/SUN MORNING...AND GENERALLY A FEW DM SHALLOWER THROUGH THE TROF ACROSS THE EAST COAST...RESULTING IN A SLOWER/WEAKER SURFACE REFLECTION INITIALLY THROUGH THE MID-ATLANTIC/GEORGES BANK VICINITY BEFORE DEEPENING NEAR NOVA SCOTIA MONDAY AFTERNOON (SEE SECTION BELOW). THE 00Z UKMET/CMC JUST LIKE THE ECMWF/GFS/NAM ALSO SHOWED AN OVERALL SLOWING TREND BUT THE UKMET/CMC ARE FAIRLY WELL CLUSTERED AT THE SURFACE BUT THE CMC TYPICAL OF ITS BIAS REMAINS GENERALLY SLOWER ALOFT WITH THE TROF PROGRESSING OFFSHORE AND THEREFORE SLOWER WITH THE COLD FRONT MOVING EAST COMPARED TO THE UKMET/NAM/GFS/ECMWF. THIS BRINGS THE 00Z NAM INTO CLOSER PROXIMITY AS WELL...BUT IS GENERALLY DRIER AND LINGERS A BIT SLOWER ALOFT WITH THE TROF ACROSS THE SOUTHEAST AND FLORIDA TO FULLY PREFER IT AT THIS TIME. AS SUCH WILL CONTINUE TO PREFER A 00Z ECMWF/UKMET BLEND AT AVERAGE CONFIDENCE. KICKER SHORTWAVE DROPPING OUT OF CANADA INTO WESTERN GREAT LAKES MONDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: AVERAGE OBVIOUSLY DOWNSTREAM EVOLUTION AND INTERACTION FROM THIS SYSTEM HAVE SIGNIFICANT EFFECTS UPON EACH OTHER. THE 12Z ECMWF/ECENS MEAN HAVE REMAINED MOST CONSISTENT THROUGH THE LAST 4 RUNS...AS NOTED IN THE RUN TO RUN ENSEMBLE SPAGHETTI PLOT...BUT WITH THE 12Z INTEGRATION THE 528DM PLOT INDICATED A SIGNIFICANT SHIFT OF THE REMAINING GUIDANCE (GEFS/CMCE/UKMET) TOWARD A MUCH LESS AMPLIFIED SYSTEM KEEPING THE NEGATIVE TILTING TROF/VORT ENERGY ACROSS NY/SE ONTARIO VS. PA/NJ THAT IS PRESENTED BY THE ECMWF SOLUTIONS AND MAYBE ONE OR TWO GEFS MEMBERS...THIS PROVIDES SOME CONCERN FOR A HIGHER CONFIDENCE IN THE CONTINUITY SOLUTION...ECMWF. THIS OBVIOUSLY PLACES SOME QUESTION ALSO ON HOW DEEP AND LEFT OF CONSENSUS THE TRACK OF THE SURFACE CYCLONE WILL BE THROUGH THE GULF OF MAINE. DO NOT WISH TO DISREGARD THE ECMWF/CONTINUITY BUT ALSO NOT DISMISS THE STRONGER CONSENSUS/TREND. AS SUCH WILL SUPPORT AN OPERATIONAL/ENSEMBLE MEAN BLEND AT SLIGHTLY BELOW AVERAGE CONFIDENCE. AS SUCH AFTER 21/12Z...A BLEND OF THE 12Z ECENS MEAN/18Z GEFS MAY BE BEST TO TEMPER THE RAPID DEEPENING WITH RESPECT TO THE SURFACE REFLECTION. 07Z UPDATE: THE 00Z ECMWF MUCH LIKE ELSEWHERE TRENDED A BIT SHALLOWER OVERALL WITH THE HEIGHT FIELD THOUGH THE ENERGY OF THE DIGGING TROF REMAINS A BIT FURTHER SOUTH THAN THE OTHER GUIDANCE ACROSS LEADING SLIGHTLY EARLIER SURFACE DEEPENING NEAR THE GULF OF MAINE...THOUGH OVERALL IS MORE IN LINE WITH OTHER GUIDANCE TO PROVIDE MORE CONFIDENCE IN AN OPERATIONAL MODEL BLEND AT AVERAGE CONFIDENCE. SHEARED UPPER LOW EXITING MEXICO INTO TX NEAR MEXICAN WEST COAST SHEARS INTO CONFLUENT SUBTROPICAL FLOW ACROSS GULF COAST THROUGH SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE MASS FIELDS ARE IN STRONG ENOUGH SUPPORT AT THIS POINT TO SUPPORT AN OPERATIONAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE WITH RESPECT TO TIMING/PLACEMENT OF THE FRONTAL ZONE AND SHEARED UPPER LEVEL WAVE PROGRESSING THROUGH THE WESTERN GULF REGION INTO THE CONFLUENT FLOW OVER THE SOUTHEAST IN ADVANCE OF DEEPENING TROF DESCRIBED IN SECTIONS ABOVE. APPROACHING STRONGER SHORTWAVE OF LARGER CUT-OFF CYCLONE NEARING PACIFIC COAST SUNDAY REMAINING UPPER LOW NEARING THE PACIFIC COAST AROUND TUESDAY...SUPPORTING A HIGH PLAINS SURFACE LOW/LEE TROF MON NIGHT INTO CENTRAL PLAINS BY TUES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/UKMET BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE THE LARGE PACIFIC GYRE CONTINUES TO ADVANCE SLOWLY TOWARD THE MEAN RIDGE OVER THE WESTERN U.S. BY SUNDAY WHEN A STRONGER WAVE ROUNDS THE BASE OF THE GYRE APPROACHING THE CA/OR. NEARLY ALL DETERMINISTIC MODELS ARE IN STRONG AGREEMENT INCLUDING THE 00Z NAM/GFS WITH TIMING/STRENGTH AND POSITION WITH THIS WAVE. HOWEVER UPSTREAM...INNER CORE DIFFERENCES ARE STARTING TO BECOME MORE NOTICEABLE AS THE CENTER TRANSITIONS EASTWARD AND/OR INTERACTS WITH THE DEEP CYCLONE ROTATING WEST AND SOUTHWEST OVER ALASKA. THE 12Z ECWMF IS IN CLOSEST PROXIMITY TO THE UPPER LOW IN AK AND BECOMES MOST INTERACTIVE...LEADING TO A BINARY INTERACTION...STALLING EASTWARD PROGRESS AS WELL ELONGATING THE UPPER LEVEL PATTERN...AS OPPOSED BY THE REST OF THE GUIDANCE THAT IS MORE TRADITIONALLY SHAPED AS A MEDIUM WAVELENGTH UPPER LOW THAT SLOWLY OPENS AS IT MAKES LANDFALL IN THE PACIFIC NORTHWEST BY THE END OF THE FORECAST PERIOD. THE 00Z NAM AND 12Z CMC ARE FASTEST IN EASTWARD PROGRESSION AWAY FROM OVERALL CONTINUITY OF FAVORING SLOWER PROGRESSION GIVEN THE MEAN RIDGE AXIS OVER THE WEST. OVERALL THE 00Z GFS/12Z UKMET AND 18Z GEFS SEEM TO BE THE MOST CENTRAL COMPROMISE...AND AS SUCH WILL FAVOR THE 00Z GFS AND 12Z UKMET (REPRESENTING THE 18Z GEFS) AT SLIGHTLY BELOW AVERAGE CONFIDENCE AFTER 21/00Z. 07Z UPDATE: THE 00Z ECMWF REMAINS GENERALLY FLATTER/ELONGATED BY THE END OF THE FORECAST PERIOD WITH THE CENTER OF THE UPPER LOW...THOUGH TRENDING TOWARD THE FASTER SOLUTION IT STILL TOO FAR FROM ITS NEXT CLOSEST/COMPARABLE SOLUTION THE 00Z UKMET. THE 00Z UKMET DID FLATTEN THE UPSTREAM RIDGE A BIT MORE THAN THE 12Z RUN BUT ALL IN ALL REMAINS FAIRLY SIMILAR. LIKEWISE THE 00Z CMC IS VERY SIMILAR TO ITS 12Z RUN AND THE 00Z NAM. AS SUCH DO NOT SEE MUCH REASON TO SHIFT THE PREFERENCE FROM A 00Z GFS/UKMET BLEND AT SLIGHTLY BELOW AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA