MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1143 PM EST WED DEC 14 2016 VALID DEC 15/0000 UTC THRU DEC 18/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z EVALUATION OF MODEL GUIDANCE INCLUDING PREFERENCE AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ POLAR VORTEX SWEEPING THROUGH ONTARIO/QUEBEC THE NEXT COUPLE OF DAYS...SURGE OF WELL BELOW NORMAL TEMPERATURES THROUGH THE SOUTHERN/EASTERN U.S ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE WATER VAPOR IMAGERY AND SURFACE OBSERVATIONS SHOWED DEEP CYCLONIC FLOW ENTRENCHING MUCH OF CENTRAL/EASTERN CANADA WITH WELL BELOW NORMAL TEMPERATURES ACCOMPANYING THE POLAR BOUNDARY. OVERALL...MODELS APPEAR TO BE IN SUFFICIENT AGREEMENT HERE ACROSS THE CONUS WITH ONLY DIFFERENCES OCCURRING AS THE CORE OF LOWER HEIGHTS MOVE THROUGH NOVA SCOTIA. THE 12Z UKMET IS WELL EAST OF THE OTHER CONSENSUS...YET GIVEN LIMITED IMPACTS TO THE CONUS A GENERAL MODEL BLEND IS SUPPORTED AT ABOVE AVERAGE CONFIDENCE. POSITIVELY-TILTED TROUGH DROPPING DOWN INTO THE NORTH-CENTRAL U.S. BY THIS WEEKEND AND PHASING WITH SHEARING SOUTHERN STREAM TROF ACROSS THE MS RIVER VALLEY BY SAT...THIS SUPPORTS SURFACE LOW AND ASSOCIATED FRONTAL ZONE CROSSING THE CENTRAL PLAINS INTO THE GREAT LAKES LATE SAT/SUN MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/12Z ECMWF CONFIDENCE: AVERAGE NORTHERN STREAM: IN THE WAKE OF THE DEEPER POLAR VORTEX...A TRAILING BROAD SHORTWAVE TROF WILL CARVE OUT THE WESTERN PORTION OF THE CANADIAN TROF AND WITH STRONG RIDGE OVER THE GULF OF ALASKA. THIS SUPPORTS NORTHERLY FLOW WITH SHORTWAVE ENERGY DIGGING INTO THE NORTHERN TIER OF THE US LATE SATURDAY AND INTO THE GREAT LAKES BY SUN. ITS TIMING WILL PLAY A KEY ROLE IN THE EVOLUTION OF THE SOUTHERN STREAM SHORTWAVE AND ASSOCIATED SURFACE WAVE. THE 12Z UKMET IS GREATEST OUTLIER AND SUPPORTS A NARROWER/SHARPER TROF AXIS THAT IS ALSO A BIT DEEPER THAN THE REMAINING GUIDANCE MAKING IT LESS FAVORABLE. THE 12Z CMC IS ALSO A BIT SUPPRESSED WITH THIS TROF AS WELL BEING BROAD BUT LESS DEEP ACROSS THE GREAT LAKES (MOSTLY PHASED WITH THE SOUTHERN STREAM). THIS LEAVES A GOOD BLEND OF THE 00Z NAM/GFS AND 12Z ECMWF REPRESENTING THE RECENT GEFS/ECENS ENSEMBLE SUITE. SOUTHERN STREAM: WOUND UP SHORTWAVE ALONG 40N WEST OF 130W WILL UNFOLD AND SHIFT EASTWARD TOWARD THE WEST COAST BY FRIDAY MORNING AS A SHORTWAVE DESCENDING OUT OF EASTERN SIDE OF THE GULF OF ALASKA TROF BECOMES DOMINANT AND SHIFTS THE POSITIVE TILTED TROF ACROSS CALIFORNIA BY SAT AND THROUGH THE SOUTHERN ROCKIES BY SAT NIGHT. CONCURRENTLY SUPPORTING SURFACE PRESSURE FALLS ALONG THE COLORADO ROCKIES THAT WILL SHIFT NORTHEAST ACROSS THE CENTRAL PLAINS WITH RETURN FLOW OUT OF THE WESTERN GULF...PROVIDING ISENTROPIC ASCENT/WAA REGIME ACROSS THE MID-MS/OHIO VALLEY. THE WAVE WILL CONTINUE TO SHEAR IN ADVANCE OF THE NORTHERN STREAM TROF. THE FASTER SOLUTIONS PRESENTED BY THE 12Z UKMET AND 00Z NAM ARE A BIT STRONGER/WOUND UP AHEAD OF THE NORTHERN STREAM HEIGHT FALLS SUPPORTING A DEEPER FURTHER NORTHWEST SURFACE SOLUTION THAN THE SLOWER MORE ELONGATED WAVE SUGGESTED BY THE 12Z ECMWF/ECENS MEAN. THE 00Z GFS HAS SLOWED AND IN DOING SO HAS SHEARED WITH LESS AMPLIFICATION ACROSS THE GREAT LAKES CLOSER TO THE ECMWF SOLUTION. THE 12Z CMC IS CLOSE TO THE GFS/ECMWF SOLUTIONS BUT AS NOTED ABOVE...IT IS MORE CONSOLIDATED AND FURTHER SOUTH AND SLOWER THAN BOTH RAISING SOME CONCERNS FOR INCLUSION WITHIN A BLEND. ALL CONSIDERED WILL CONTINUE WITH CONTINUITY FAVORING THE ECWMF/ECENS MEAN SOLUTION WHILE INCLUDING A BIT MORE GFS PERCENTAGE AS IT IS BECOMING MORE FAVORABLE AND CLOSER TO THE OVERALL AVERAGE OF ALL MODELS. CONFIDENCE IS AVERAGE IN THE 00Z GFS/12Z ECMWF BLEND GIVEN THE OVERALL PATTERN IS COMING TO CONSENSUS; YET THE SMALLER DETAILS (WHICH ARE NOT MINOR TO WX IMPACTS) REMAIN VARIABLE RUN TO RUN. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA