MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1205 PM EDT SUN SEP 25 2016 VALID SEP 25/1200 UTC THRU SEP 29/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ DEEP CYCLONE MOVING NEAR THE US/CANADIAN BORDER BEFORE MOVING SOUTH THROUGH CENTRAL GREAT LAKES TUES/WED...FRONT THROUGH EAST COAST BY WED MIDDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/NAM AND 00Z UKMET BLEND CONFIDENCE: ABOVE AVERAGE MODEL AGREEMENT IS VERY STRONG THROUGH MUCH OF THE DEPTH OF CYCLONE THROUGH 27/12Z WITH ONLY THE 00Z CMC LAGGING EVER SO SLIGHTLY. SLIGHT DIFFERENCES MANIFEST IN THE TIMING/SHAPE OF THE FRONTAL ZONE THROUGH NEW ENGLAND ON TUESDAY EVENING WITH THE 00Z UKMET/ECMWF BOTH SUGGESTING A STRONGER TRIPLE POINT AND PROGRESSING FRONT THROUGH NEW ENGLAND MUCH FASTER THAN THE GFS. THIS SEEMS PLAUSIBLE GIVEN THE STRENGTH OF DARKENING SEEN IN WV/STRATOSPHERIC INTRUSION CURRENTLY SEEN OVER ND...SO TO HEDGE WILL BLEND THE SUITE WITH THIS TIMING. AFTERWARD...SPREAD INCREASES ALOFT MAINLY WITH THE OCCLUSION/UPPER LOW ACROSS THE GREAT LAKES. THE 00Z CMC BEING FURTHER WEST KEEPS RIDGING BETWEEN THIS ENERGY AND DESCENDING SHORTWAVE ENERGY FROM THE DAVIS STRAIT/LABRADOR SEA. THE REST OF THE GUIDANCE BREAKS THE RIDGE AND SHOWS A CONNECTION LEADING TO AN ELONGATED TROF THAT DESCENDS INTO THE LOWER CENTRAL GREAT LAKES AND EVENTUALLY UPPER OHIO VALLEY BY THE END OF THE FORECAST PERIOD. THE 00Z ECMWF WHICH HAS THE BIAS OF BEING A BIT SLOWER AND MORE WOUND UP LIVES UP TO ITS BIAS...AND THEREFORE IS A BIT FURTHER WEST AND LESS ELONGATED THAT THE 00Z UKMET AND 12Z NAM/GFS. THIS PLACES THE ECMWF ON THE WESTERN PERIPHERY OF BEST GUIDANCE INCLUDING WEST(SOUTHWEST) OF 00Z ECENS MEAN. AT THE SFC THIS MANIFESTS AS A FASTER WEAKENING AND TRANSITION ACROSS THE OHIO RIVER VALLEY AND LEE SIDE CAROLINA DEVELOPMENT BY WED NIGHT. THE 00Z UKMET IS A BIT MORE ELONGATED WITH THE TROF SSW TO NNE THAN THE 12Z NAM OR GFS. THE 12Z GFS TRENDED A BIT WEST CLOSER TO THE 00Z ECENS MEAN OVERALL...HOWEVER KEEPS IN GOOD CONTINUITY WITH PRIOR RUNS AS WELL. GIVEN THE ECMWF CONTINUES TO SHOW POOR CONTINUITY/CHANGING APPEARANCE OVER THE PAST FEW DAYS WILL FAVOR A 12Z GFS/NAM AND 00Z UKMET BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. CLOSED LOW IN E AZ/W NM MAKING ANTICYCLONIC LOOP ACROSS NW MEXICO INTO S CA/W AZ BY TUE/WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE REMARKABLE AGREEMENT IN SHAPE/TIMING AND PLACEMENT EXIST WITH THE DEVELOPING CLOSED LOW AFTER THE ANTICYCLONIC WAVE BREAK IN NM TODAY THROUGH MUCH OF THE FORECAST TIME PERIOD. AS THE SYSTEM LIFTS NORTH THROUGH THE LOWER COLORADO RIVER VALLEY THE 12Z NAM AND GFS BEGIN TO ELONGATE AND LIFT SLIGHTLY FASTER UNDER INFLUENCE OF INCREASING SWLY FLOW/DIGGING TROF IN THE PACIFIC NORTHWEST. THIS IS ONLY NOTICEABLE AFTER 12Z ON THE 28TH...AND AS SUCH THERE IS LITTLE TO SUGGEST CHANGING A GENERAL MODEL BLEND PREFERENCE AT THIS TIME. CONFIDENCE REMAINS VERY HIGH IN THIS BLEND'S EVOLUTION. SYSTEM CLIPPING THE PACIFIC NORTHWEST MON NIGHT/TUES WITH TAIL END OF FRONTAL ZONE THROUGH MT/ND WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE WHILE THERE IS SOME SPREAD WITH THE SHORTWAVE AND SURFACE REFLECTION IN TIMING WITH THE 00Z CMC/ECMWF FASTER THAN THE UKMET AND 12Z GFS/NAM. HOWEVER THE TRAILING EDGE OF THE FRONT CLIPS THE NORTHWEST AND CROSSES THE NORTHERN US ROCKIES TUES INTO WED WITH VERY SIMILAR SPEED/SHAPE AND ORIENTATION TO SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE. TROF DIGGING TOWARD PACIFIC NORTHWEST BY WED EVENING/THURSDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE A MORE CONCENTRIC DEEPER CYCLONE ADVANCES SOUTHEASTWARD TOWARD BC AND THE PACIFIC NORTHWEST WITH BROAD SWLY FLOW ACROSS WA/OR/N CA BY THE END OF THE FORECAST PERIOD. MASS FIELDS ARE REMARKABLY SIMILAR IN TIMING/STRENGTH AND SHAPE OF THE WAVE TROUGH THE TROPOSPHERIC COLUMN. THE 12Z NAM AND 00Z CMC ARE SLIGHTLY DEEPER BUT WELL WITHIN SPEC TO SUPPORT GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE EVEN AT THIS FAR OUT IN TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA