MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1229 AM EST SUN DEC 4 2016 VALID DEC 04/0000 UTC THRU DEC 07/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS MODEL EVALUATION INCLUDING MODEL PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ WESTERN MEXICO CLOSED LOW EJECTING NORTHEASTWARD ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z ECMWF/UKMET/CMC BLEND CONFIDENCE: NEAR AVERAGE A LARGE AND ANOMALOUS UPPER LEVEL LOW OVER WESTERN MEXICO AT THE BEGINNING OF THE PERIOD IS FORECAST TO TRACK EASTWARD ACROSS MEXICO AND REACH TEXAS BY MONDAY. BEYOND THIS TIME, THIS FEATURE IS PROGGED TO GRADUALLY TRANSITION INTO AN OPEN WAVE ACROSS THE EASTERN U.S. BEFORE BECOMING ABSORBED INTO THE OVERALL FLOW. OVERALL MODEL AGREEMENT IS GOOD THROUGH 12Z MONDAY WITH THE UPPER LOW TRACKING ACROSS NORTHERN MEXICO. BY THE TIME THE LOW ENTERS TEXAS, THE 00Z NAM BECOMES FARTHER NORTH THAN THE MODEL CONSENSUS AND THE GFS SLIGHTLY MORE AMPLIFIED WITH THE TROUGH AXIS CROSSING THE DEEP SOUTH THROUGH 12Z TUESDAY. THERE ARE MINOR TIMING DIFFERENCES AMONG THE MODELS AS THIS FEATURE DAMPENS OUT, BUT NO MAJOR OUTLIERS ARE IMMEDIATELY APPARENT. NORTHERN U.S. SHORTWAVE REACHING NEW ENGLAND BY MONDAY NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-UKMET MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE A PROGRESSIVE NORTHERN STREAM SHORTWAVE TROUGH OVER THE CENTRAL AND NORTHERN PLAINS SUNDAY MORNING IS FORECAST TO TRACK RAPIDLY EASTWARD ACROSS THE GREAT LAKES WHILE ACQUIRING NEGATIVE TILT, WITH AN UPPER LEVEL RIDGE DIRECTLY AHEAD OF IT. BY THE TIME IT REACHES NEW ENGLAND, IT IS EXPECTED TO SHEAR OUT AND BECOMING MORE ZONALLY ORIENTED. MODELS HAVE CONTINUED TO SHOW DECENT AGREEMENT OVERALL WITH RESPECT TO TIMING. THE UKMET IS THE MOST AMPLIFIED SOLUTION AND HAS A STRONGER SURFACE LOW OVER NEW ENGLAND ON MONDAY. THE OTHER MODEL SOLUTIONS ARE RELATIVELY WELL CLUSTERED. SOUTHERN CANADA CLOSED LOW WITH SURFACE LOW DEVELOPMENT OVER NORTHERN PLAINS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~ PREFERENCE: 12Z ECMWF CONFIDENCE: AVERAGE PACIFIC SHORTWAVE ENERGY TRAVERSING THE U.S./CANADIAN BORDER EARLY IN THE PERIOD IS FORECAST TO JOIN FORCES WITH AN UPPER LEVEL LOW OVER SOUTH CENTRAL CANADA BY TUESDAY. THE DIFFLUENT REGION ALOFT IN ASSOCIATION WITH THIS FEATURE WILL ALLOW FOR SURFACE LOW DEVELOPMENT OVER THE NORTHERN PLAINS. THE NAM IS A STRONG SOUTHERN OUTLIER WITH THE 500MB LOW THROUGH 00Z TUESDAY. THE UKMET IS SLOWER WITH THE TROUGH PROGRESSION THAN THE MODEL CONSENSUS. THE ECWMF CONTINUES TO BE CLOSE TO THE MODEL CONSENSUS AND THUS IS THE PREFERRED CHOICE FOR THIS SYSTEM. SHORTWAVE TROUGH REACHING THE INTERMOUNTAIN WEST BY TUESDAY NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL 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 AS A BROADER AND LESS AMPLIFIED WAVE. GIVEN ISSUES DOWNSTREAM IN TIMING, THE 12Z CMC HAS A SLIGHTLY DIFFERENT ORIENTATION OF THE WAVE BUT IN A GENERAL SENSE THE TIMING/DEPTH/PLACEMENT OF THE WAVE IS IN GOOD AGREEMENT AND THERE IS SOLID ENSEMBLE SUPPORT TO SUGGEST A GENERAL MODEL BLEND AS PREFERENCE. CONFIDENCE IS SLIGHTLY ABOVE AVERAGE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... HAMRICK