MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 141 PM EST SAT NOV 22 2014 VALID NOV 22/1200 UTC THRU NOV 26/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. SHORTWAVE SPURRING LOW PRESSURE IN THE DAKOTAS TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: UKMET/CANADIAN/NAM COMPROMISE CONFIDENCE: AVERAGE DIFFERENCES WITH SHORTWAVE STRENGTH ALOFT LEAD TO SIGNIFICANT SURFACE PRESSURE ISSUES WITH A LOW PRESSURE SYSTEM MOVING INTO THE DAKOTAS TUESDAY, WITH THE 12Z GFS THE WEAKEST AND THE 12Z ECMWF THE STRONGEST. A SOLUTION ON THE WEAKER SIDE OF THE GUIDANCE MAKES SENSE GIVEN THE QUICK AND NON-AMPLIFIED FLOW PATTERN IN THAT AREA. HOWEVER, THE 12Z UKMET/12Z CANADIAN/12Z NAM ARE SOMEWHAT STRONGER THAN THE INTERMEDIATE 00Z ECMWF/12Z GEFS/09Z SREF MEAN SOLUTIONS, AND ARE PREFERRED WITH AVERAGE CONFIDENCE CONSIDERING THE SYSTEM'S QUICK MOVEMENT THROUGH THE FLOW PATTERN. CONSOLIDATED MIDWESTERN TROUGH ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-GFS/NON-GEFS COMPROMISE CONFIDENCE: ABOVE AVERAGE MUCH LIKE OVERNIGHT, CONVECTIVE/GRIDSCALE FEEDBACK HAUNTS THE 12Z GFS OPERATIONAL AND PARALLEL SOLUTIONS (AND LIKELY THE 06Z GEFS MEAN DUE TO SIMILAR PHYSICS) WHICH USE MULTIPLE HUGE VERTICAL MOTION BULL'S EYES ASSOCIATED WITH AN APPARENT SQUALL LINE AND CONVECTION IN THE MIDWEST TO OVER-DEEPEN THE SURFACE LOW MOVING FROM THE MID-MISSISSIPPI VALLEY THROUGH THE GREAT LAKES (INTO THE MID TO UPPER 960S HPA). THIS SUBSEQUENTLY CAUSES THE GFS/GEFS MEAN COLD FRONTS TO WHIP EASTWARD FASTER THAN THE REMAINDER OF THE GUIDANCE. THE PREFERENCE IS FOR A 12Z NAM/12Z CANADIAN/12Z UKMET/12Z ECMWF COMPROMISE FOR THE ENTIRE SYSTEM WITH ABOVE AVERAGE CONFIDENCE. WITH THIS PREFERENCE, RECORD LOW SEA LEVEL PRESSURE VALUES FOR NOVEMBER ARE POSSIBLE IN LOCATIONS SUCH AS GRAND RAPIDS AND SAULT SAINTE MARIE MI SUNDAY NIGHT INTO MONDAY MORNING. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ROTH