MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1157 AM EST SUN DEC 27 2015 VALID DEC 27/1200 UTC THRU DEC 31/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z EVALUATION INCLUDING MODEL PREFERENCE AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ WEAK SOUTHERN STREAM SHORTWAVE AND ASSOCIATED SURFACE LOW EJECTING ACROSS THE NORTHEAST THROUGH SUN... NORTHERN STREAM TROUGH SKIRTING NEW ENGLAND THROUGH MON... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE OVERALL MODEL AGREEMENT REMAINS STRONG WITH HANDLING OF WEAK ENERGY LIFTED OUT OF THE SOUTHERN STREAM IN ADVANCE OF FAST MOVING NORTHERN STREAM TROF THAT SLIDES ACROSS ONTARIO INTO NORTHERN MAINE BY SUNDAY NIGHT/MONDAY MORNING. THE SOUTHERN STREAM S/W HAS AN ATTENDANT SURFACE WAVE ALONG STRONG SURFACE FRONT THAT EXTENDS BACK ACROSS MISSISSIPPI VALLEY. EVENTUALLY THE WEAK SURFACE WAVE FILLS OVER NEW ENGLAND IN FAVOR OF DEVELOPING COASTAL LOW OFF CAPE COD INTO THE GULF OF MAINE MIDDAY TODAY. WITH OVERALL STRONG AGREEMENT AN OPERATIONAL MODEL BLEND IS PREFERRED AT ABOVE AVERAGE CONFIDENCE. DEEP CLOSED LOW OVER THE UPPER RIO GRANDE VALLEY ENERGY/SURFACE LOW LIFTING NORTHEAST THROUGH THE GREAT LAKES BY TUES AND SHEARING THROUGH THE NORTHEAST BY WED... DEVELOPING NORTHEAST COASTAL LOW TUES NIGHT/WED MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/GFS/00Z ECMWF BLEND - WEIGHTED TOWARD 00Z ECMWF CONFIDENCE: AVERAGE MODELS CONTINUE TO HAVE RUN TO RUN CONSISTENCY AND TIGHT AGREEMENT WITH THEIR OWN ENSEMBLE SUITE EXCEPT FOR THE 00Z UKMET WHICH SHIFTED EAST AND WEAKER FROM ITS 26/12Z RUN TOWARD THE GFS/GEFS CAMP. THE 12Z NAM/00Z ECMWF REMAIN TIGHTLY CLUSTERED ON THE WESTERN SIDE OF THE SUITE BEING STRONGER WITH TIGHTER LOW LEVEL THERMAL GRADIENTS. HOWEVER...SURFACE CYCLONE IS VERY STRONG AND WEST WITH AN OCCLUSION TOWARD DFW EARLY IN DAY ONE (06Z) MORE SO THAN THE OTHER DETERMINISTIC (INCLUDING THE NAM)...AND GIVEN CURRENT SURFACE CONDITIONS SEEMS A BIT MISPLACED PARTICULARLY IN THE THERMAL FIELDS. GIVEN THE NAM'S BIAS TENDENCY FOR STRONGER/DEEPER SOLUTIONS AND THE ECMWF'S AGREEMENT WITH IT...AND THE 00Z UKMET SHIFTING TOWARD A WEAKER/EASTERN SOLUTION IT BEGS THE QUESTION OF FULL SUPPORT OF THE ECWMF. ANOTHER INTERESTING BUT CONFLICTING PIECE OF INFORMATION IS THE 00Z ECMWF RUN APPEARS TO BE ON THE EASTERN DOMAIN OF ITS 00Z ENSEMBLE SUITE...PARTICULARLY IN WEAKENING/SHEARING OUT THE WAVE ON DAY 3 AS IT SHIFTS EAST. THE 00Z UKMET'S SHIFT DOES REDUCE CONFIDENCE IN THE NAM/ECMWF SOLUTION AND IT WAS DRAMATICALLY WEAKER THAT IT WAS FIRST/FASTEST TO SHEAR OUT THE LOW ACROSS THE GREAT LAKES...ACCELERATING IT INTO NEW ENGLAND THROUGH DAY 3 INCLUDING A NORTHERLY SURFACE LOW WITHIN THE GULF OF MAINE 30/00Z WED...WHICH HAD LITTLE SUPPORT IN THE ENSEMBLE OR OTHER DETERMINISTIC SUITES. THE 00Z AND 12Z GFS REMAIN QUITE SIMILAR...AND APPEAR TO BE ON THE WESTERN SIDE OF THE GEFS SUITE...CLOSER TO THE ECMWF/NAM...THOUGH THERMALLY SPEAKING HAVE THE LOOSEST/FLATTER THERMAL GRADIENTS WITHIN THE OPERATIONAL SUITE...AND GIVEN THE ANOMALOUS NATURE TO THE THERMAL/MOISTURE PROFILES WOULD EXPECT A BIT MORE LATENT HEAT RESPONSE TO FEEL OVERALL SIGNIFICANT CHANGE IN CONFIDENCE. HOWEVER...GIVEN ISSUES WITH ECMWF/NAM REDUCING PROBABILITY IN OVER-STRENGTHENING...WILL BEGIN TO INCLUDE SOME GFS INTO THE BLEND IN ACCORDANCE WITH PREFERENCES IN QPF (PLEASE SEE QPFPFD). THE 00Z CMC HAS A SIMILAR FLAVOR OF THE 00Z UKMET/GFS BUT IS STRONG AND SOUTH WITH THE COASTAL LOW DEVELOPMENT TO FAVOR IT HEAVILY OR AT ALL IN THE BLEND AT THIS TIME. AS SUCH A 12Z NAM/GFS/00Z ECMWF BLEND IS PREFERRED THOUGH HIGHLY WEIGHTED TOWARD THE ECMWF AT AVERAGE CONFIDENCE. SHORTWAVE TROUGH MOVING INTO THE WEST SUN...DEEPENING ACROSS THE SOUTHWEST TUES...EJECTING INTO SOUTHERN PLAINS WED LINGERING ENERGY SHED ON NW SIDE OF PRIOR SYSTEM EVOLVES TO CENTROID OF LARGER SCALE TROF OVER NORTHER RED RIVER VALLEY WED INTO THURS. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND THROUGH 29/12Z 12Z GFS/00Z ECMWF/CMC BLEND AFTERWARD CONFIDENCE: ABOVE AVERAGE...BECOMING AVERAGE AFTER 29/12Z. A SHORTWAVE TROUGH JUST OFFSHORE OF PACIFIC NORTHWEST WILL SHIFT ASHORE SUNDAY NIGHT AS THE BASE BEGINS TO DROP IN LATITUDE DIGGING OUT A DEEPER LARGE SCALE TROF INTO THE SOUTHWEST TUESDAY WITH FAIRLY STRONG AGREEMENT IN THE GLOBAL MODELS AND ENSEMBLE MEANS. AS THE WAVE EJECTS WED MORNING INTO THE PLAINS THE MODELS REMAIN AGREEABLE IN THE PLACEMENT/TIMING OF THE ENERGY BUT START TO INTERACT DIFFERENTLY WITH LINGERING/SHEARED ENERGY LEFT ACROSS THE DAKOTAS/MINNESOTA FROM THE PRIOR DOWNSTREAM UPPER LOW SHEARING OUT WHILE OVER-TOPPING THE RIDGE IN PLACE IN THE OHIO VALLEY. THIS LINGERING ENERGY CONSOLIDATES TO BECOME THE CENTROID OF THE EXPANDING/BROADENING LARGE SCALE TROF OVER THE WEST AND GREAT PLAINS BY THE END OF THE FORECAST PERIOD. THE 12Z NAM IS GENERALLY...TYPICAL TO ITS BIAS... STRONGER WITH THE WAVE ENERGY EJECTING INTO THE PLAINS BUT IS MUCH STRONGER AND FURTHER WEST AS IT CLOSES THE UPPER LOW OVER THE DAKOTAS. THE 00Z ECMWF TO BE EXPECTED...GIVEN DOWNSTREAM AGREEMENT IS ALSO A BIT STRONGER WITH THIS CENTROID ENERGY BUT LESSER SO THAN THE NAM...BUT REMAINS IN GOOD AGREEMENT WITH THE EJECTING BASE OF THE WAVE. THE 00Z UKMET TYPICAL OF THE BIAS BECOMES FAST BUT ALSO SHEARS VERY LITTLE ENERGY BACK TO THE WEST UNLIKE MUCH OF THE MODEL/ENSEMBLE SUITE TO SUPPORT IT. THE 00Z CMC LOOKS LIKE A GOOD BLEND BETWEEN THE GFS/ECMWF TO BE INCLUDED. OVERALL AGREEMENT IS STRONG ENOUGH PRIOR TO 29/12Z TO SUPPORT AN OPERATIONAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE...THOUGH INTERACTION WITH LINGERING UPPER-LOW ENERGY ADDS INCREASED SPREAD AND REDUCED CONFIDENCE OVER THE NORTHERN RED RIVER VALLEY AND GREAT LAKES BY THE END OF THE FORECAST... SO PREFERENCE IS BLEND OF 12Z GFS AND 00Z ECMWF/CMC AT AVERAGE CONFIDENCE. COMPACT SHORTWAVE MOVING INTO THE PACIFIC NORTHWEST BY WED PHASING WITH STALLED/BLOCKED FLOW OVER BC THAT DROPS INTO WESTERN SIDE OF LARGE SCALE TROF OVER GREAT BASIN BY WED EVENING. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z GFS AND 00Z UKMET/ECMWF CONFIDENCE: AVERAGE THE MODELS SHOW A FAIRLY COMPACT SHORTWAVE AND SMALL CLOSED LOW CENTER MOVING INTO THE PACIFIC NORTHWEST TUES NIGHT AND WED. THE ENERGY WILL BE TRAVERSING A MEAN RIDGE AXIS AND WILL BE WEAKENING AS IT ARRIVES. THE 12Z NAM AND 00Z CMC ARE A LITTLE MORE PROGRESSIVE THAN THE SLIGHTLY WEAKER 12Z GFS AND STRONGER 00Z ECMWF/UKMET. OVERALL GIVEN THE SIZE OF THE WAVE MOVING OVER THE MEAN RIDGE AXIS TOWARD SLOWER/BLOCKED FLOW OVER SW CANADA...THE ENSEMBLES GENERALLY WASH THE WAVE OUT AND ARE NOT NECESSARILY HELPFUL. AS SUCH WILL CONTINUE TO PREFER A BLEND OF THE 12Z GFS/00Z UKMET/ECMWF AT AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA