MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 139 PM EST MON DEC 05 2016 VALID DEC 05/1200 UTC THRU DEC 09/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE MODEL INITIALIZATION ERRORS APPEAR NEGLIGIBLE WITH RESPECT TO THEIR FORECASTS ...NORTHERN MEXICO CLOSED LOW EJECTING NORTHEASTWARD TOWARDS THE EAST COAST... PREFERENCE: 12Z ECMWF/GFS/UKMET COMPROMISE CONFIDENCE: NEAR AVERAGE THE UPPER LEVEL LOW CURRENTLY OVER NORTHERN MEXICO IS FORECAST TO TRACK NORTHEASTWARD AND EVOLVE INTO A PROGRESSIVE OPEN WAVE ALOFT AS IT BEGINS TO WEAKEN/FILL. 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 INTENSIFIES OFFSHORE LATER IN THE PERIOD. THE NAM WAS A BIT NORTH OF THE UKMET/ECMWF/GFS BY THE TIME THE VORT REACHES THE MID ATLANTIC COAST. WHILE NOT TERRIBLY FAR FROM THE CONSENSUS LATITUDE...THE 05/12Z NAM WAS MORE COMPACT AND STRONGER THAN THE OTHER GUIDANCE. ...NORTHERN U.S. SHORTWAVE SHEARING OUT ACROSS NEW ENGLAND BY MONDAY NIGHT... PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE A NEGATIVELY TILTED NORTHERN STREAM SHORTWAVE CURRENTLY CENTERED OVER QUE WITH A LOBE OF VORTICITY EXTENDING ACROSS PARTS OF NEW ENGLAND WILL CONTINUE TO SHEAR AS IT MOVES EAST/NORTHEAST. THE 12Z MODELS APPEARED TO HANDLE THIS FEATURE IN A SIMILAR FASHION...SO A GENERAL MODEL BLEND SHOULD CONTINUE TO BE FINE HERE. ...SOUTHERN CANADA CLOSED LOW WITH SURFACE LOW DEVELOPMENT OVER NORTHERN PLAINS... PREFERENCE: 05/12Z NCEP/UKMET BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE SHORTWAVE ENERGY CURRENTLY OVER THE NORTHERN ROCKIES WILL CONTINUE TO ROTATE AROUND THE SOUTHERN PERIPHERY OF THE UPPER LEVEL VORTEX THAT IS STARTING TO FORM OVER SASKATCHEWAN. THE COLD FRONT ASSOCIATED WITH THE SURFACE LOW WILL USHER IN THE FIRST NOTEWORTHY ARCTIC AIRMASS OF THE SEASON. GIVEN THE DOWNSTREAM UPPER LEVEL CONFIGURATION, THE TIMING OF THIS SHORTWAVE WILL DETERMINE THE MAGNITUDE OF DEEPENING OVER THE EASTERN DAKOTAS AND MINNESOTA BY EARLY TUESDAY. THE 12Z NCEP MODELS WERE MORE AGGRESSIVE IN ROTATING SHORTWAVE ENERGY AROUND THE BASE OF THE LARGER MID/UPPER LEVEL CYCLONE. DESPITE THE DIFFERENT WAYS IN WHICH THE MODELS HANDLE THE SHORTWAVE ENERGY...MANY OF THE DIFFERENCES OVER THE LOWER 48 IRON THEMSELVES OUT BY THE END OF DAY 3. ...SHORTWAVE TROUGH CROSSING THE GREAT BASIN TUE TO THE CENTRAL ROCKIES WED... PREFERENCE: 05/12Z UKMET/NCEP BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN UPPER LOW OVER THE GULF OF ALASKA WILL BEGIN TO SHEAR OUT AS IT HEADS TOWARDS BRITISH COLUMBIA TODAY AND TONIGHT. THE SHORTWAVE ENERGY ASSOCIATED WITH THIS IS EXPECTED TO CROSS THE PACIFIC NORTHWEST BEFORE SETTLING ACROSS THE GREAT BASIN ON TUESDAY, AND THEN EJECT ACROSS THE CENTRAL PLAINS WEDNESDAY. THE 12Z NCEP GUIDANCE SEPARATED THEMSELVES FROM THE 00Z NON NCEP GUIDANCE BY BEING MORE AMPLIFIED ONCE THE ENERGY REACHES THE CENTRAL ROCKIES LATE WEDNESDAY AND THURSDAY. THE NON NCEP GUIDANCE GENERALLY KEPT TO THE IDEA SHOWN IN THEIR PREVIOUS RUNS. GIVEN THE AMOUNT OF UPSTREAM RIDGING...THINK THE NCEP IDEA OF MARGINALLY LOWER HEIGHTS EAST OF THE CENTRAL ROCKIES FITS BETTER. ...SYSTEM APPROACHING THE PAC NW COAST BY END OF DAY 3... PREFERENCE: NON 12Z GFS BLEND CONFIDENCE: AVERAGE THE MODELS WERE IN GENERALLY GOOD AGREEMENT WITH THE APPROACH OF THE NEXT TROF AND ASSOCIATED PRECIPITATION. THE ONE EXCEPTION WAS THE 12Z GFS WHICH WAS CONSIDERABLY FASTER. GIVEN THE DOWNSTREAM FLOW PATTERN...THINK THAT THE WAVELENGTHS INVOLVED WITH ARGUE AGAINST THE GFS. THE LACK OF A WELL DEFINED JET NOSING IN FROM THE ERN NOPAC SEEMS WHICH WOULD AID THE LOWERING OF HEIGHTS OVER THE PAC NW ALSO ARGUES AGAINST THE GFS IDEA. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BANN