MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1119 AM EST TUE DEC 27 2016 VALID DEC 27/1200 UTC THRU DEC 31/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ COLD FRONT CROSSING THE EAST COAST/SOUTHEAST TOWARD THE GULF TODAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE MODELS SHOW SUFFICIENT SIMILARLY WITH TO HAVE HIGH CONFIDENCE IN A GENERAL MODEL BLEND FOR THIS SYSTEM. KICKER SHORTWAVE MOVING INTO THE GREAT LAKES TODAY AND NORTHEAST WED MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE NO SIGNIFICANT DIFFERENCES WERE NOTED WITH THIS SYSTEM THROUGH WED...AT WHICH POINT THE TROUGH AXIS MOVES OFFSHORE. SMALLER DEPTH DETAILS LEAD TO SOME GREATER SPREAD BUT MILD THROUGH SOUTHEAST CANADA AND NORTHWEST ATLANTIC. THIS IS MINOR OVERALL AND AS SUCH A GENERAL MODEL BLEND IS RECOMMENDED TO SMOOTH OUT THESE SMALLER SCALE DIFFERENCES. CONFIDENCE IS ABOVE AVERAGE. UPPER TROUGH AMPLIFYING FROM THE NORTHWEST TO THE EAST COAST THROUGH THU WITH DEEP NEW ENGLAND COASTAL SURFACE LOW DEVELOPING THU NIGHT INTO FRIDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM AND 00Z UKMET/ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE TRAIN OF SMALLER SHORTWAVE ENERGY PACKETS CONTINUE START ENTERING THE PACIFIC NORTHWEST TODAY ALONG STRONG FAIRLY ZONAL JET. THESE SHORTWAVE PACKETS CONTINUE TO REDUCE IN LENGTH EVENTUALLY SUPPORTING A BROADER AMPLIFICATION INTO A SOLID TROF BY EARLY THURS ACROSS THE UPPER MS VALLEY INTO THE GREAT LAKES WITH BROAD SURFACE TROF DEVELOPING ACROSS ONTARIO THROUGH THE OHIO/CENTRAL APPALACHIANS THURS. STRONG SHORTWAVE ENERGY AT THE BASE OF THE TROF WILL HAVE A SLIGHT NEGATIVE TILT INTO A BROADLY DIFFLUENT UPPER PATTERN SPARKING RAPID SURFACE PRESSURE FALLS WITH A DEEP LOW DEVELOPING THURS EVENING/FRIDAY ACROSS THE EASTERN SEABOARD TOWARD NEW ENGLAND ON FRIDAY. ENSEMBLE SPREAD IS FAIRLY TIGHT FOR SUCH A STRONG/RAPIDLY EVOLVING SYSTEM YET...TIMING DIFFERENCES OF THE ENERGY ROUNDING THE BASE LEAD TO SMALL SPATIAL DIFFERENCES BUT LARGER QPF/WINTER WX IMPACTS ACROSS NEW ENGLAND (PLEASE REFER TO QPFPFD AND QPFHSD FOR ADDITIONAL DETAILS). THE GFS HAS BEEN AND CONTINUES TO BE WITH THE 12Z GFS A BIT FASTER WITH THE ENERGY REACHING THE BASE OF THE TROF AND EVENTUAL DEEPER CYCLONE OFF THE NORTHEAST COAST FRIDAY. THE SLIGHTLY SLOWER SOLUTIONS OF THE ECMWF/12Z NAM AND 00Z UKMET ARE MUCH BETTER CLUSTERED AND SUPPORTED A BIT BETTER BY THE ENSEMBLE SOLUTIONS INCLUDING PRIOR CYCLES. THE 00Z CMC WHILE BETTER ALIGNED WITH THE ECMWF/UKMET/NAM BUT IN THE LOWER LEVELS THE CMC IS A CLEAR SE/WEAK OUTLIER IN THE ENSEMBLE SFC LOW CLUSTER...AS SUCH IS LESS FAVORABLE IN THE BLEND. AS SUCH A BLEND OF THE 12Z NAM AND 00Z ECMWF/UKMET IS PREFERRED. CONFIDENCE IN THIS BLEND IS SLIGHTLY ABOVE AVERAGE GIVEN THE OVERALL PATTERN IS FAIRLY TIGHT AND THE MASS FIELDS ARE DEPICTING VERY SIMILAR EVOLUTIONS WITH MINOR (THOUGH IMPORTANT) TIMING DIFFERENCES. MID-LEVEL LOW OFF OF SOUTHWEST U.S. COAST APPROACHING CALIFORNIA BY END OF WEEK ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/00Z ECMWF BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE MODELS ARE IN FAIRLY GOOD AGREEMENT THROUGH THE SW WOBBLE OF THE CLOSED MID-LEVEL LOW OFF THE SOUTHWEST COAST THROUGH ABOUT THURSDAY. HOWEVER WITH THE APPROACH OF THE LARGER SCALE TROF TOWARD THE NORTH...THE SYSTEM STARTS TO WEAKEN A BIT AND LIFT INTO THE WESTERLY FLOW...EVENTUALLY REACHING SOUTHERN CALIFORNIA BY MIDDAY FRIDAY WITH MODERATE SPREAD IN TIMING AND SHAPE. THE 00Z UKMET CONTINUES TO BE LIFTED FURTHER NORTH AND THE 12Z NAM CONTINUES TO SHIFT FASTER EAST WHILE RETAINING SOME CONSOLIDATED VORT ENERGY IN THE CENTER. THE 00Z CMC IS VERY SIMILAR IN TIMING TO THE NAM (FASTER) BUT IS VERY WEAK WITHIN THE ENSEMBLE SPECTRUM. WHILE THE 00Z ECMWF IS ON THE WESTERN SIDE OF THE ECENS MEMBERS; IT IS WELL SHAPED/TIMED WITH THE GEFS/12Z GFS THOUGH SLIGHTLY SLOWER (FURTHER WEST) BUT A GOOD COMPROMISE TOWARD THE MIDDLE OF ALL SOLUTIONS WITH FAIRLY SOLID RUN TO RUN CONTINUITY. AS SUCH WILL SUPPORT A 12Z GFS/00Z ECMWF BLEND TO BEST REPRESENT THIS MIDDLE GROUND/ENSEMBLE SOLUTION. CONFIDENCE REMAINS SLIGHTLY ABOVE AVERAGE IN THIS BLEND GIVEN ITS STRENGTH IN CONTINUITY AS WELL. LEAD SHORTWAVE ENERGY OF LARGER SCALE TROF REACHES SW BC BY EARLY THURSDAY TREKKING ACROSS SW CANADA INTO THE NORTHERN TIER OF THE US BY FRIDAY EVENING WITH ACCOMPANYING SURFACE LOW ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/00Z ECMWF BLEND CONFIDENCE: AVERAGE AS THE NORTHERN PORTION OF THE NEXT LARGER SCALE WAVE APPROACH THE BC COAST IT SUPPORTS SOLID HEIGHT FALLS AND CYCLONIC SPIN UP AT THE SURFACE AS WELL AS IN THE MID-LEVELS. THERE IS FAIRLY SOLID MODEL AGREEMENT OF THE 12Z NAM/GFS AND 00Z ECMWF THROUGH THIS TIME PERIOD... AS THE CMC IS SLOW (AND REMAINS SO THROUGH THE ENTIRE FORECAST PERIOD) AND THE 00Z UKMET BECOMES VERY AMPLIFIED/DEEP CYCLOGENESIS BY 29/18Z JUST OFFSHORE. AS THE WAVE CROSSES THE SOUTHERN CANADIAN ROCKIES...THE UKMET RETAINS SOME ENERGY BUT ALSO REMAINS ON THE FAST SIDE OF THE GUIDANCE IN LINE WITH A KNOW BIAS. OTHERWISE THE NAM/ECMWF/GFS REMAIN WELL TIMED...THOUGH START TO SPLIT IN DEPTH. THE 12Z NAM LIKE A TYPICAL DAY 3 BIAS BECOMES VERY WOUND UP...WHILE THE ECMWF IS FLATTER WEAKER. THE GFS SPLITS THE DIFFERENCE NEARER THE ECMWF (WHICH ALSO REPRESENTS THE GENERAL ENSEMBLE SPREAD). AS SUCH A 12Z GFS/00Z ECMWF BLEND IS PREFERRED AND WITH MODERATE BUT WHAT APPEARS TO BE CONVERGING SOLUTIONS, CONFIDENCE IS AVERAGE. REMAINING PORTION OF POSITIVELY TILTED UPPER TROUGH OVER ENTERING THE NORTHWEST THU NIGHT. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECMWF CONFIDENCE: SLIGHTLY BELOW AVERAGE GIVEN THE BULK OF ENERGY SHED IN THE FASTER NORTHERN STREAM AS WELL AS SOME OF TH BASE LEADING TO ANTICYCLONIC WAVE BREAK AND CLOSE LOW GENERATION SOUTH OF 40N AND WEST OF 140W...THERE REMAINS A LARGE AMOUNT OF MODEL SPREAD ON HANDLING THE REMAINING PORTION OF THE LARGER SCALE POSITIVELY TILTED TROF OVER THE NORTHEAST PACIFIC ENTERING THE PACIFIC NORTHWEST TOWARD THE END OF THE WEEK. STILL THE ENSEMBLES WERE COMING TO A MORE COMMON SOLUTION WITH THE GEFS STILL A BIT FASTER THAN THE ECENS MEAN. THIS IS BEST REPRESENTED BY THE 00Z ECMWF. THE 12Z NAM CONTINUES TO BE STRONG AND QUITE PROGRESSIVE LIKELY WITH SOME INTERACTION WITH THE DEEPER CLOSE LOW LIFTING OUT OF THE SUBTROPICAL EASTERN PACIFIC. THE 00Z UKMET HAS A SIMILAR SHAPE/EVOLUTION TO THE ECMWF BUT DUE TO A FURTHER NORTH SUBTROPIC INTERACTION LIKE THE NAM IS A BIT FORWARD. THIS IS NOW PARTICULARLY THE CASE THE 12Z GFS SHOWED A SIGNIFICANT SHIFT FROM ONE OF THE PROGRESSIVE SOLUTIONS 3 CYCLES AGO TO SLOWING PAST THE ENSEMBLE MEANS TOWARD THE SLOWEST SOLUTION...HIGHLY POSITIVELY TILTED (ALMOST BY 90 DEGREES) AND IN LINE WITH THE LESS FAVORABLE VERY SLOW 00Z CMC. ALL CONSIDERED WPC PREFERENCE IS THE 00Z ECMWF THOUGH INCLUSION OF THE 06Z GEFS AND 00Z ECENS MEAN WOULD BE ADVISABLE IF AVAILABLE TO BLEND. GIVEN THE PATTERN/SETUP AND RUN TO RUN VARIABILITY CONFIDENCE REMAINS SLIGHTLY BELOW AVERAGE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA