MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 149 AM EST SUN MAR 13 2016 VALID MAR 13/0000 UTC THRU MAR 16/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z GUIDANCE EVALUATION INCLUDING MODEL PREFERENCES AND FORECAST CONFIDENCE SHORT WAVE TRACKING AFFECTING NORTHERN NEW ENGLAND SAT NIGHT/SUN...SURFACE COLD FRONT CROSSING NEW ENGLAND SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE 00Z NAM/GFS CONTINUE TO FALL WITHIN THE STRONG AGREEMENT WITH THE TRACK OF THE SHORTWAVE MOVING ACROSS ME BY SUN. THE TIMING OF THE COLD FRONT IS VERY STRONG THOUGH THERE REMAINS SOME SMALL SPREAD IN EXACT PLACEMENT OF THE SURFACE LOW WHEN TRANSFERRING ENERGY TO THE NEW CENTER/TRIPLE POINT OFF SHORE BETWEEN 12-18Z SUNDAY. SO WILL CONTINUE TO FAVOR AN OPERATIONAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE. THE 12Z NAM AND GFS FALL INTO LINE WITH THE CONSENSUS CONCERNING THE TRACK OF THE SHORT WAVE AS IT MOVES ACROSS NORTHERNMOST NEW ENGLAND SUN. WHILE THERE IS SOME SPREAD IN THE PLACEMENT OF THE SURFACE LOW ASSOCIATED WITH THE SHORT WAVE...THERE IS GOOD AGREEMENT WITH THE TIMING OF THE COLD FRONT CROSSING NEW ENGLAND SUN. REMAINING SHEARED UPPER LOW ACROSS AR AND SURFACE LOW TRACKING FROM THE MID MS VALLEY TO GREAT LAKES MONDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM AND 12Z UKMET/ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE AGREEMENT CONTINUES TO TIGHTEN WITH THE WEAKENING UPPER LOW AS IT SHEARS THROUGH THE MEAN RIDGE ACROSS THE GREAT LAKES EVENTUALLY PHASING WITH THE SHORTWAVE ENERGY CURRENTLY IN E WA...AS THEY MERGE IN E CANADA BY TUES. THERE ARE A FEW TIMING DIFFERENCES ASSOCIATED WITH THE REMAINING AMPLIFICATION/CONSOLIDATION OF THE WAVE LEADING TO SLOWER NORTHWARD PROGRESSION...WITH THE 12Z ECMWF SLOWEST ALONG WITH THE 12Z UKMET... BOTH 00Z GFS/12Z CMC ARE FASTEST...WHILE THE 00Z NAM IS MORE CENTRAL. THERE REMAINS SOME DIFFERENCES IN THE SENSIBLE WEATHER FIELDS DUE TO THIS TIMING...BUT OVERALL SEEMS TO BE MORE FIRMLY DRIVEN BY THE INTERACTIONS TO THE MORE DOMINANT FEATURES (SHORTWAVE ACROSS SOUTHERN PLAINS OR THE CANADIAN TRACK - SHORTWAVE). CONTINUITY FAVORS THE DEEPER/SLOWER TRENDS LEADING TO THE 00Z NAM AND 12Z UKMET/ECMWF BLEND AS PREFERENCE. CONFIDENCE IS SLIGHTLY ABOVE AVERAGE. UPPER LOW TROF TRACKING ACROSS THE SOUTHERN PLAINS SUN/SUN NIGHT...BEFORE WEAKENING ACROSS THE OH VALLEY/MID ATLANTIC MON AND ASSOCIATED SURFACE LOW IN THE MS/OH RIVER VALLEYS AS WELL AS SURFACE DEVELOPMENT ALONG MID-ATLANTIC COAST TUES. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z ECMWF/UKMET/CMC BLEND CONFIDENCE: AVERAGE MODEL AGREEMENT IS FAIRLY GOOD WITH THE TIGHTLY WOUND SHORTWAVE CROSSING THE SOUTHERN PLAINS ON DAY 1...BUT AFTER THAT POINT THE PLACEMENT/TIMING OF THE ENERGY BEGINS TO DIVERGE AS THE OVERALL WAVE STARTS TO WEAKEN A BIT. 12Z ENSEMBLES STRONGLY SUPPORT THE 12Z ECMWF INCLUDING MANY OF THE GEFS MEMBERS WHILE THE 12Z GFS WAS FARTHEST SOUTH IN THE SURFACE CLUSTER. IT SHOULD BE NOTED THE 12Z ECMWF IS ALSO ON THE NORTHERN SIDE OF THE CLUSTER TOO...THOUGH RUN TO RUN CONTINUITY FAVORS THE NORTHERN PORTION OF THE CLUSTER MAYBE NOT AS DRAMATIC AS THE CMC/ECMWF OPERATIONAL RUNS SPECIFICALLY. INTERESTINGLY THE UPPER LEVEL SHORTWAVE FOR THE GFS SHIFTS MORE DUE EAST THEN SSE ACROSS THE WESTERN ATLANTIC WHICH IS SUPPORTED BY 00Z NAM. HOWEVER THE 00Z TRACKS SIMILAR ALOFT IT ALSO DEVELOPS A SURFACE WAVE NEARER THE ECMWF/CMC/UKMET THOUGH FARTHER NORTHEAST FROM THE ENSEMBLE SURFACE CLUSTER...KEEPING IT UNFAVORABLE. THE 12Z UKMET GENERALLY QUITE AMPLIFIED AND SHOWS ITS FAST SPEED BIAS TOWARD DAY 3...GIVEN A STRONGER WAVE FURTHER NORTH...IT ALSO RESULTS IN STRONG QPF FEEDBACK (TYPICAL OF BIAS AS WELL THOUGH THIS APPEARS OVER THE TOP TOO). STILL WILL FAVOR A NON-NCEP BLEND AT AVERAGE CONFIDENCE TO BEST REPRESENT THE 12Z ECENS MEAN...THOUGH FAVORING THE ECMWF MORE HEAVILY IN THE WEIGHTING. INCLUSION OF THE 18Z GEFS/12Z ECENS MEAN TO THIS BLEND IF POSSIBLE SHOULD STRENGTHEN MASS FIELD SHAPE/PLACEMENT OF FEATURES THOUGH MAGNITUDES WILL BE DULLED BY INHERENT AVERAGING. SHORT WAVE COMING ASHORE NEAR CA/OR EARLY MON AND EVOLVING INTO A BROAD CLOSED LOW INTO THE NORTHERN PLAINS TUE/WED. ASSOCIATED DEEP SURFACE TROF/LOWS IN LEE OF ROCKIES MON/TUES...DEEPENING ACROSS THE MIDWEST/W GREAT LAKES WED. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM/GFS AND 12Z ECMWF BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE MODELS ARE GENERALLY WELL HANDLED FOR THE LEAD SHORTWAVE MOVING OUT OF E WA ATTM PARTICULARLY THROUGH MONDAY EVENING WHEN THE EFFECTS FROM INCREASING SPREAD ARE WELL INTO CANADA. AS THE REST OF THE WAVE ENTERS THE U.S. THE LEAD SHORTWAVE LATE SUN/EARLY MONDAY...BECOMES THE CENTROID/FULCRUM OF THE DEVELOPING UPPER LOW ACROSS THE HIGH PLAINS ALONG THE US/CANADA BOARDER TUESDAY...WHILE THE STRONG ONSHORE FLOW UNDERNEATH WILL AMPLIFY THE WAVE/NEGATIVE TILT ACROSS THE EASTERN PLAINS/MIDWEST BY TUES EVENING/WED MORNING. ALL MODELS GENERALLY AGREE UPON THE OVERALL EVOLUTION OF THE DUAL VORTICITY FEATURES IN THE TROF...HOWEVER DIFFERENCES IN TIMING OF THE FEATURES PLAY A SIGNIFICANT ROLE IN OVERALL SHAPE BY THE END OF THE FORECAST PERIOD. DIFFERENCES IN TIMING AND WHICH FEATURE IS FAVORED LEAD TO DIFFERENCES IN FAVORED SURFACE LOW(S) WITHIN THE BROAD SURFACE LEE TROF FROM SE ALBERTA TO THE BLACK HILLS TO E CO/W KS BY 15/00Z...THE MORE WRAPPED UP THE UPPER LOW TO THE NORTH...FAVORS THE NORTHERN CYCLONE ACROSS THE DAKOTAS VERSUS A STRONGER SHORTWAVE THROUGH THE GREAT PLAINS DEEPENING THE SOUTHERN TRACK CYCLONE QUICKER INTO THE MIDWEST BY TUESDAY NIGHT. THE 00Z NAM IS A LITTLE LESS FOCUSED WITH THE LEAD WAVE AND EVENTUALLY SHEARS OUT FAVORING THE EASTERN PORTION OF THE TROF INTO THE UPPER MIDWEST...IN A SIMILAR MANNER TO THE 12Z ECMWF THOUGH A BIT FASTER OVERALL THOUGH HAVING SHEARED THE ENERGY OF THE NORTHERN CENTROID PULLS ADDITIONAL COLDER AIR FURTHER SOUTH POTENTIALLY LEADING TO SOME ISSUES WITH P-TYPE...PLEASE REFER TO QPFHSD FOR FURTHER DETAILS. THE 00Z GFS WHICH HAD BEEN TRENDING FASTER/STRONGER AS BACKED UP FROM ITS STRONGER NORTHERN STREAM SOLUTION PRESENTED BY THE 18Z RUN AND THOUGH THE 00Z RUN IS BETTER ALIGNED WITH THE 00Z NAM/12Z ECMWF AND THE 12Z GEFS/ECENS MEANS...IT REMAINS A BIT FASTER IN TIMING AND THEREFORE A BIT EAST OF THE PREFERRED TRACK OF THE NAM/ECMWF. THIS SLOWER SOLUTION WAS ALSO SUPPORTED BY THE 12Z GFS PARALLEL RUN ADDING SOME CONFIDENCE TOWARD THAT DIRECTION AS WELL. THE 12Z UKMET IS VERY STRONG WITH THE SOUTHERN SHORTWAVE/WELL AMPLIFIED AND RESULTS IN THE DEEPEST SURFACE REFLECTION WELL SOUTH OF THE BEST ENSEMBLE CLUSTER (THOUGH IT REMAINS GENERALLY BROAD). OVERALL WILL FAVOR A 12Z ECMWF WITH 00Z NAM/GFS BLEND FAVORING THE FORMER TWO MODELS OVER THE GFS IN THE WEIGHTING. OVERALL THE BROAD SPREAD AND TIMING DIFFERENCES WITH A DUAL FOCUSED WAVE LIKE THIS DOES NOT PROVIDE TREMENDOUS CONFIDENCE...A SLIGHT BIT BELOW AVERAGE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA