MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1205 AM EST TUE DEC 6 2016 VALID DEC 6/0000 UTC THRU DEC 9/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE MODEL INITIALIZATION ERRORS APPEAR NEGLIGIBLE WITH RESPECT TO THEIR FORECASTS STRONG SHORTWAVE OVER TEXAS MOVING NORTHEASTWARD TOWARDS THE EAST COAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~ PREFERENCE: 12Z ECMWF/00Z GFS/00Z NAM COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE UPPER LEVEL SHORTWAVE TROUGH OVER EASTERN TEXAS IS FORECAST TO TRACK NORTHEASTWARD AND REMAIN A PROGRESSIVE OPEN WAVE ALOFT. IT SHOULD THEN WEAKEN ONCE IT EMERGES OVER THE WESTERN ATLANTIC SINCE IT WILL BE ENTERING A RIDGE AXIS. AT THE SURFACE, A SURFACE LOW WILL TRACK INLAND WEST OF THE APPALACHIANS WHILE A SECOND SURFACE LOW FORMS NEAR THE NORTH CAROLINA COAST AND THEN MOVES OFFSHORE. THE 12Z UKMET APPEARS A LITTLE MORE AMPLIFIED WITH THE SHORTWAVE ENERGY AS IT TRACKS FROM THE DEEP SOUTH TO THE MID-ATLANTIC REGION BUT IS SIMILAR WITH TIMING. THE 12Z CMC SHOWS SLIGHTLY MORE RIDGING DOWNSTREAM FROM THE TROUGH. THE 00Z NAM HAS COME INTO BETTER AGREEMENT WITH THE MODEL CONSENSUS COMPARED TO ITS EARLIER RUN. SHEARING NORTHEASTERN U.S. SHORTWAVE EXITING TUESDAY MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE A NEGATIVELY TILTED NORTHERN STREAM SHORTWAVE CURRENTLY CENTERED OVER QUEBEC AND MAINE WITH A LOBE OF VORTICITY EXTENDING ACROSS PARTS OF NEW ENGLAND WILL CONTINUE TO SHEAR OUT AS IT MOVES EASTWARD. THE CURRENT MODEL SUITE IS IN GOOD AGREEMENT ON THIS FEATURE AND THEREFORE A GENERAL MODEL BLEND IS RECOMMENDED. SOUTHERN CANADA CLOSED LOW WITH SURFACE LOW OVER UPPER MIDWEST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/12Z ECMWF BLEND CONFIDENCE: NEAR AVERAGE SHORTWAVE ENERGY CURRENTLY OVER THE NORTHERN PLAINS WILL CONTINUE TO ROTATE AROUND THE SOUTHERN PERIPHERY OF THE UPPER LEVEL VORTEX THAT IS FORMING OVER SASKATCHEWAN AND MANITOBA. THE COLD FRONT ASSOCIATED WITH THE SURFACE LOW WILL USHER IN THE FIRST NOTEWORTHY ARCTIC AIRMASS OF THE SEASON. THE 12Z UKMET IS FARTHER SOUTH WITH THE SURFACE LOW OVER NORTHERN MINNESOTA COMPARED TO THE MODEL CONSENSUS, AND ALSO SHARPER WITH THE SURFACE COLD FRONT. THERE APPEARS TO BE GOOD OVERALL AGREEMENT WITH THE TIMING OF THE COLD FRONTAL PASSAGE ACROSS THE CENTRAL AND EASTERN U.S. EARLY IN THE PERIOD. THERE IS MORE SPREAD WITH THE SECONDARY COLD FRONT THAT IS FORECAST TO CROSS THE GREAT LAKES AND OHIO VALLEY LATER IN THE PERIOD, WITH THE NAM STRONGER WITH THIS FRONT. SHORTWAVE TROUGH TRACKING FROM THE GREAT BASIN TO THE CENTRAL PLAINS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ PREFERENCE: 00Z NAM/00Z GFS/18Z GEFS MEAN CONFIDENCE: NEAR AVERAGE A SHORTWAVE TROUGH NEAR VANCOUVER ISLAND AT THE BEGINNING OF THE FORECAST PERIOD WILL CROSS THE PACIFIC NORTHWEST BEFORE SETTLING ACROSS THE GREAT BASIN ON TUESDAY EVENING, AND THEN EJECT ACROSS THE CENTRAL PLAINS WEDNESDAY AS A BROAD UPPER LEVEL TROUGH. THE 00Z NAM IS A BIT MORE PRONOUNCED WITH THE TROUGH AXIS, AND THE 00Z GFS IS CLOSE TO THAT SOLUTION. GIVEN THE AMOUNT OF UPSTREAM RIDGING OVER THE EASTERN PACIFIC DURING THIS TIME, WE THINK THE NAM/GFS IDEA OF MARGINALLY LOWER HEIGHTS OVER THE ROCKIES AND WESTERN HIGH PLAINS SEEMS MORE REASONABLE. STORM SYSTEM APPROACHING THE PACIFIC NORTHWEST COAST BY FRIDAY MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~ PREFERENCE: 12Z EC MEAN/18Z GEFS MEAN BLEND CONFIDENCE: BELOW AVERAGE THE GREATEST AMOUNT OF MODEL DISAGREEMENT DURING THE SHORT-RANGE FORECAST PERIOD IS ASSOCIATED WITH A STRONG LOW PRESSURE SYSTEM TRACKING TOWARDS THE PACIFIC NORTHWEST COAST BY THURSDAY NIGHT. THE GFS IS THE FASTEST SOLUTION BRINGING THE SURFACE LOW CLOSEST TO THE COAST BY 00Z FRIDAY. THE ECMWF APPEARS TOO WEAK WITH THE LOW AND MORE ELONGATED THAN THE OTHER SOLUTIONS. THE UKMET AND NAM ARE AMONG THE STRONGEST SOLUTIONS. UNTIL BETTER AGREEMENT BECOMES APPARENT, AN ENSEMBLE APPROACH FOR THIS SYSTEM IS PROBABLY BEST FOR NOW. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... HAMRICK