MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1141 PM EST MON NOV 10 2014 VALID NOV 11/0000 UTC THRU NOV 14/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ================================================== 00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES ================================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ================================================== ...WINTER STORM AFFECTING THE UPPER GREAT LAKES... PREFERENCE: ANY OF 00Z NAM/GFS...AND 12Z ECMWF/UKMET LOW PRESSURE LIFTING INTO SOUTHERN WISCONSIN EARLY TUESDAY WILL LIFT INTO SOUTHEAST ONTARIO BY WEDNESDAY MORNING...CARRYING WITH IT A SWATH OF SNOW ACROSS THE UPPER GREAT LAKES. WITH THIS WEATHER SYSTEM NOW IN THE MATURING PHASE AND EMBEDDED ENTIRELY WITHIN THE UPPER AIR NETWORK THE MODEL TRENDS HAVE BEEN MINIMAL SINCE THE 10/12Z CYCLE. THE OPERATIONAL MODELS CLUSTER CLOSELY...ESPECIALLY THROUGH DAY 1 WHEN THIS SYSTEM IS IMPACTING THE U.S. THE ONLY THING THAT COULD BE CHARACTERIZED AS AN OUTLIER IS THE 12Z CANADIAN...BEING SLIGHTLY SLOW AND CERTAINLY HEAVIER WITH ITS PRECIPITATION OUTPUT. ...ARCTIC OUTBREAK IN THE ROCKIES/CENTRAL U.S...AND ASSOCIATED UPPER FLOW... PREFERENCE: BLEND OF 00Z GFS WITH 12Z UKMET/CANADIAN THE OPERATIONAL MODELS HAVE SHOWN A LOT OF SIMILARITY IN THE LOW LEVELS FOR SEVERAL CYCLES...AND ARE NOW SHOWING LESS VARIABILITY IN THE MID LEVELS. RECENT RUNS OF THE ECMWF HAVE TENDED TO LEAN TOWARD THE DEEP SIDE OF THE ENSEMBLES WITH RESPECT TO THE TROUGH AXIS SWINGING THROUGH THE CENTRAL PLAINS AND MIDWEST STATES WED/THU. THE OTHER MODELS HAVE BEEN EQUALLY CONSISTENT IN FORECASTING SOMETHING MORE IN LINE WITH A CONSENSUS OF THE ENSEMBLE MEANS. GIVEN THAT THIS TROUGH IS SWINGING OUT ATOP A VERY STABLE ARCTIC AIRMASS...THE DEEP SOLUTION OF THE ECMWF APPEARS LESS LIKELY. THE GFS/UKMET/CANADIAN ARE BEST REPRESENTATIVE OF CONSENSUS. THE NAM COULD BE INCLUDED IN OUR PREFERENCE THROUGH DAY 2. THEN SOME DIFFICULTIES UPSTREAM BEGIN TO INFLUENCE ITS MID LEVEL PATTERN OVER THE PLAINS. ...SYSTEM SKIRTING THE OUTER BANKS OF NORTH CAROLINA... PREFERENCE: BLEND OF 12Z ECMWF/UKMET THERE ARE SOME SIGNIFICANT DIFFERENCES WITH THIS SYSTEM...BUT MAINLY OUT IN THE OPEN WATERS OF THE WESTERN ATLANTIC. IN TERMS OF EFFECTS ON THE CONUS...SOME LIGHT PRECIPITATION IS FORECAST IN THE OUTER BANKS OF NORTH CAROLINA...WITH RELATIVELY GOOD AGREEMENT. IN TERMS OF THE SYSTEM STRUCTURE... THE GFS IS SYSTEMATICALLY QUICKER THAN THE ECMWF IN DEVELOPING A CLOSED SURFACE LOW AND LIFTING IT NORTHWARD. ENSEMBLE TRENDS WOULD SEEM TO FAVOR SOMETHING SLOWER THAN THE GFS...BUT PERHAPS A LITTLE FASTER THAN THE ECMWF. BLENDING THE ECMWF TOWARD THE UKMET WOULD PRODUCE A SOLUTION CLOSER TO THE ENSEMBLE CONSENSUS. THE GFS COULD NEARLY BE BLENDED AS WELL...BUT ITS MID LEVEL WAVE APPEARS TO DE-AMPLIFY AT THE SAME TIME THAT THE SURFACE LOW IS MATURING...WHICH DOES NOT APPEAR REALISTIC. THE NAM IS EXCLUDED FROM THE PREFERENCE AS IT MARKS THE SOUTH AND WEST EDGE OF THE ENVELOPE WITHOUT MUCH SUPPORT. ...MOIST ONSHORE FLOW INTO THE WEST ON WED/THU... PREFERENCE: BLEND OF 00Z GFS WITH 12Z ECMWF/UKMET A LOW AMPLITUDE SOUTHERN STREAM SHORTWAVE IS EXPECTED INTO NORTHERN CALIFORNIA ABOUT THE SAME TIME THAT NORTHERN STREAM FLOW FLATTENS ACROSS THE PACIFIC NORTHWEST...ALL OF WHICH YIELDS ENHANCED ONSHORE FLOW PUSHING EVEN INTO THE INTERMOUNTAIN REGION. MODELS DIFFER AS TO THE MID LEVEL DETAILS...GIVEN LOW AMPLITUDE FLOW...BUT THEIR LOW LEVEL FORECASTS ARE GENERALLY SIMILAR...AND PRECIPITATION FORECASTS ARE CONVERGING TOWARD A BETTER DEFINED CONSENSUS. THE GFS/ECMWF/UKMET ARE ESPECIALLY WELL REPRESENTATIVE OF THE CONSENSUS. THE NAM BECOMES AN OUTLIER ON DAY 3 WITH ITS SOUTHERN STREAM WAVE BEING SLOWER AND NORTHERN STREAM TROUGH ANCHORING MUCH FARTHER WEST THAN THE MODEL CONSENSUS. THE CANADIAN IS ALSO VERY SLOW IN THE SOUTHERN STREAM...BUT ITS PRECIPITATION OUTPUT IS RELATIVELY NEAR THE CONSENSUS. ...SOUTH TEXAS... PREFERENCE: BLEND OF 00Z GFS WITH 12Z ECMWF/CANADIAN AT THE TAIL END OF THE SURGING ARCTIC BOUNDARY SOME ORGANIZED PRECIPITATION IS FORECAST OVER FAR SOUTH TEXAS. THERE IS LITTLE DEFINITION TO THE MID LEVEL FLOW...SO THIS APPEARS FORCED PRIMARILY BY THE LOW LEVEL FRONTAL ZONE. THE GFS/ECMWF/CANADIAN ARE PREFERRED...WHEREAS THE NAM IS WETTER AND THE UKMET IS DRIER THAN CONSENSUS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE