MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1209 PM EDT MON MAY 05 2014 VALID MAY 05/1200 UTC THRU MAY 09/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS MODEL EVALUATION ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. TROUGH MOVING THROUGH THE WEST INTO THE HIGH PLAINS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECMWF/06Z GFS COMPROMISE CONFIDENCE: AVERAGE THE MODELS/ENSEMBLES SHOW A DEEP LAYER TROUGH WITH EMBEDDED 700-500 MB LOW WITHIN THE TROUGH ORIGINATING OVER NV 00-12Z TU AND CONTINUING DOWNSTREAM ACROSS UT/CO/WY AND THEN THE CENTRAL TO NORTHERN PLAINS. TYPICAL TIMING AND PHASING DIFFERENCES DEVELOP WITH THE 00Z ECMWF TYPICALLY A FEW HOURS SLOWER THAN THE REST OF THE MODELS/ENSEMBLE MEANS. THE 00Z ECMWF ENSEMBLE MEAN IS A FEW HOURS FASTER THAN THE 00Z OPERATIONAL ECMWF TIMING AS THE TROUGH EMERGES FROM THE ROCKIES ACROSS THE HIGH PLAINS AND AREAS FURTHER EAST. THE 12Z GFS TRENDED A FEW HOURS FASTER WITH TYPICAL RUN TO RUN DIFFERENCES. CLOSED LOW TYPICALLY MOVE SLOWLY SO WHETHER THE FASTER 12Z RUN IS A CORRECT TREND REMAINS TO BE SEEN AND I WOULD WAIT UNTIL OTHER MODEL AGREE ON THE TREND BEFORE MAKING WHOLESALE CHANGES FOR THE 12Z GFS. THE 09Z SREF MEAN DEAMPLIFIES THE 500 MB TROUGH FASTER THAN THE ECMWF/GFS/UKMET/NAM AND RESPECTIVE GEFS/ECMWF ENSEMBLE MEANS...SO THE 09Z SREF MEAN IS THE LEAST PREFERRED FORECAST. WITH THE 12Z NAM 1-2 DM LOWER THAN THE MODEL/ENSEMBLE MAJORITY...IT IS ALSO CONSIDERED A LOW PROBABILITY FORECAST. THE NAM TIMING AGREES WELL WITH THE MODEL/ENSEMBLE MAJORITY...WHICH CLUSTER BETWEEN THE 06Z GFS/ECMWF/UKMET AND THE RESPECTIVE GFS/ECMWF ENSEMBLE MEANS. THERE IS AVERAGE CONFIDENCE DUE TO TYPICAL DAY 2-3 TIMING/AMPLITUDE DIFFERENCES WITH THE CLOSED LOW. SYSTEM APPROACHING THE PACIFIC NORTHWEST THURSDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/00Z ECMWF COMPROMISE CONFIDENCE: AVERAGE THE MODELS SHOW A PERSISTENT CLOSED LOW SFC/ALOFT IN THE NORTHEAST PACIFIC WITH A MID LEVEL WAVE ROTATING SOUTH OF THE PARENT LOW AND LIKELY SPURRING SECONDARY CYCLOGENESIS WEST OF VANCOUVER ISLAND AND BRITISH COLUMBIA THU. ALOFT, THE SHORTWAVE IS MOVING OVER A BROAD RIDGE, WHICH SHOULD LEAD TO A SYSTEM WEAKER THAN SEEN IN THE 06Z GFS SOLUTION. THE 12Z GFS HAS SHOWN A LOWER AMPLITUDE 700-500 BM TROUGH AND WEAKER SFC REFLECTION...NOW CLUSTERING BETTER WITH THE 00Z ECMWF/09Z SREF MEAN/00Z CANADIAN/00Z UKMET. THE 12Z NAM HAS A HIGHER AMPLITUDE TROUGH/DOWNSTREAM RIDGE AT 700 MB RESULTING IN A FURTHER SOUTH SFC LOW. SINCE THE 700 MB WAVE SHOULD BE MUTED IN AMPLITUDE AS TRAVERSES THE CONFLUENT FLOW/STRONG JET FLOW OVER THE TOP OF THE BROAD RIDGE, SO THE 12Z NAM IS CONSIDERED A LOW PROBABILITY SOLUTION. A COMPROMISE OF THE 00Z ECMWF/12Z GFS SOLUTIONS SHOULD REFLECT THE SIMILAR TIMING AND MITIGATE THE INTENSITY ISSUES AMONG THE INDIVIDUAL MODELS. WAVY FRONT IN THE SOUTHERN MID ATLANTIC TO SOUTHEAST ~~~~~~~~ PREFERENCE: MODEL CONSENSUS CONFIDENCE: ABOVE NORMAL THE MODELS SHOW HIGH PRESSURE BUILDING EAST ACROSS THE GREAT LAKES AND ONTARIO/QUEBEC...WHICH DRIVES THE COLD FRONT IN THE SOUTHERN MID ATLANTIC SLOWLY SOUTH INTO THE SOUTHEAST. THE MODELS/SREF MEAN/GEFS MEAN ARE IN GOOD AGREEMENT ON THE FRONT PROGRESSION/TIMING. A MODEL CONSENSUS SHOULD MITIGATE DETAIL DIFFERENCES. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... PETERSEN