MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1109 AM EST SUN DEC 04 2016 VALID DEC 04/1200 UTC THRU DEC 08/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ WESTERN MEXICO CLOSED LOW EJECTING NORTHEASTWARD WITH MILLER-B SETUP OVER EASTERN US BY TUES/WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM AND 00Z UKMET/ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE SPREAD CONTINUES TO REDUCE WITH TIME AS THE SYSTEM BECOMES MORE FOCUSED WITHIN THE DATA NETWORK AND STARTS TO LIFT OUT OF MEXICO. THE 00Z ECMWF/UKMET AND ECENS MEAN HAVE BE MORE CONSISTENT AND STABLE OVER THE LAST DAY OR SO NOW THAT THE ECENS MEAN HAS SLOWED. THE 12Z NAM TRENDED SLOWER AND MORE IN SYNC WITH THESE SOLUTIONS. THOUGH IN THE FINAL STAGES BEFORE FULLY WEAKENING OUT THE NAM TRACKS A BIT NORTH RATHER THAN SHIFTING EAST LIKE THE UKMET/ECMWF LEADING TO MINOR DIFFERENCES NOTED BY THE END OF DAY 3 MAKING IT A BIT LESS FAVORABLE AT THAT TIME FRAME YET STILL USEFUL IN THE BLEND/CONFIDENCE BUILDER. THE 00Z CMC IS QUICK TO WEAKEN AND IS INFLUENCED NEGATIVELY BY THE OVER AMPLIFIED AND EASTWARD SHIFTED UPPER LOW DEVELOPING IN THE UPPER MIDWEST. THIS MAKES IT LESS DESIRABLE AS A WHOLE. THE 12Z GFS WHILE INDICATING SOME SLIGHTLY FASTER TREND TOWARD THE COMMON SOLUTION REMAINS SLOW PARTICULARLY AFFECTING DIFFERENCES ACROSS THE TN/UPPER OH VALLEY/APPALACHIANS AND LESSER SO OVER THE SOUTHEAST COASTAL PLAIN. ALL CONSIDERED THOUGH...A 00Z ECMWF/UKMET WEIGHTED BLEND WITH THE 12Z NAM IS WPC PREFERENCE AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. NORTHERN U.S. SHORTWAVE SHEARING THROUGH NEW ENGLAND BY MONDAY NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE A PROGRESSIVE NORTHERN STREAM SHORTWAVE TROUGH OVER THE WESTERN MIDWEST THIS MORNING IS FORECAST TO TRACK RAPIDLY EASTWARD ACROSS THE GREAT LAKES WHILE ACQUIRING NEGATIVE TILT AS IT SHEARS WEST TO EAST OVER THE UPPER LEVEL RIDGE DIRECTLY AHEAD OF IT AND BY THE TIME IT REACHES NEW ENGLAND IT BECOMES MORE ZONALLY ORIENTED. MODELS INDICATE SOLID AGREEMENT TO SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE. SOUTHERN CANADA CLOSED LOW WITH SURFACE LOW DEVELOPMENT OVER NORTHERN PLAINS BY TUES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/GFS AND 00Z ECMWF BLEND CONFIDENCE: AVERAGE SHORTWAVE ENERGY CURRENTLY OVER SW BC WILL CONTINUE TO DROP SE ACROSS THE US ROCKIES AND BY ROTATING AROUND THE SOUTHERN PERIPHERY OF THE UPPER LEVEL PIVOT THAT IS STARTING TO FORM OVER SASKATCHEWAN. GIVEN DOWNSTREAM UPPER LEVEL CONFIGURATION...THE TIMING OF THIS SHORTWAVE WILL DETERMINE THE MAGNITUDE OF RAPID DEEPENING OVER THE RED RIVER VALLEY BY EARLY TUESDAY. THE 12Z GFS CONTINUES TO BE THE FASTER SOLUTION AND AS SUCH WILL HAVE THE BEST CONFIGURATION FOR A DEEPER MORE CONCENTRIC UPPER LOW EVOLUTION WHILE WOBBLING EASTWARD EARLIER INTO NW/N CENT ONTARIO. YET THE 12Z RUN HAS TRENDED A BIT SLOWER/WESTWARD WHICH APPEARS POSITIVE TOWARD THE OVERALL SPREAD. THE 00Z ECMWF IS SLOWER TO REACH THE SE PERIPHERY OF THE UPPER LOW AND SO DEEPENS LATER AND SUPPORTS A MORE ELONGATED E-W UPPER LEVEL PATTERN WHILE SUPPORTING A WOUND UP SURFACE CIRCULATION FURTHER WEST FOR LONGER TIME. WHILE THE GEFS SOLUTIONS FOLLOW THE GFS WELL...THE 00Z ECENS MEMBERS SPLIT THE DIFFERENCE OF THE TWO WITH THE OPERATIONAL ECMWF BEING ON THE WESTERN THIRD OF SOLUTIONS. THE 12Z NAM TRENDED A BIT FASTER AND TIMES WELL WITH THE ECMWF THROUGH TUESDAY...BUT EVOLVES MORE CONCENTRICALLY AND SHIFTS EASTWARD LIKE THE GFS (JUST SLOWER IN TIME) ACTING AS A MIDDLE GROUND PROXY FOR THE TWO SOLUTIONS. THE 00Z CMC IS SLOW BUT ALSO A CLEAR OUTLIER FORMING THE CLOSED LOW OVER THE NW GREAT LAKES AND THE 00Z UKMET WHILE SIMILAR TO THE ECMWF IS EVEN FURTHER SLOWER MAKING IT APPEAR ON THE FAR EXTREME OF 00Z ECENS MEMBERS. AS SUCH A BLEND OF THE 12Z NAM/GFS AND 00Z ECMWF APPEARS TO BE A GOOD REPRESENTATION OF THE ENSEMBLE SOLUTIONS THOUGH THE REMAINING SPREAD IS LARGE ENOUGH BASED ON SUCH SHORT TIMING DIFFERENCES TO HAVE AN AVERAGE CONFIDENCE IN THE BLEND COMING TO FRUITION. SHORTWAVE TROUGH CROSSING THE GREAT BASIN LATE TUES AND INTO THE CENTRAL PLAINS BY LATE WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS AND 00Z UKMET/ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE GULF OF ALASKA UPPER LOW UNDER THE INFLUENCE OF A LARGER GLOBAL SCALE TROUGH ACROSS NORTHWESTERN CANADA BEGINS TO SHEAR OUT ALONG THE BRITISH COLUMBIA COAST ON MONDAY. THE SHORTWAVE ENERGY ASSOCIATED WITH THIS IS EXPECTED TO CROSS THE PACIFIC NORTHWEST BEFORE SETTLING ACROSS THE GREAT BASIN ON TUESDAY AND EJECTING INTO THE CENTRAL PLAINS BY WED. TIMING OF THE WAVE SEEMS TO LEAD TO THE LARGEST SPREAD IN GUIDANCE THOUGH AS THE WAVE EJECTS INTO THE PLAINS ON WED...THE MIDDLE GROUND IN TIMING 12Z NAM IS MOST AMPLIFIED TYPICAL OF ITS KNOWN DAY 3 NEGATIVE BIAS. THE 12Z GFS TRENDED A BIT SLOWER THAN THE 06Z GFS/GEFS BUT REMAIN A BIT FASTER THAN THE MAJORITY OF OTHER GUIDANCE. THE 00Z ECMWF/UKMET ARE BOTH ON THE SLOWER SIDE BUT YET WITHIN THE BULK OF ENSEMBLE SOLUTIONS AND BECOME A BIT MORE AMPLIFIED AT 7H THOUGH NOT AS DRASTIC AS THE 12Z NAM. THE 00Z CMC IS SLOWER AND MORE BROAD THAN THE REST OF THE GUIDANCE. AS SUCH WILL SUPPORT AT 12Z GFS AND 00Z UKMET/ECMWF BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA