MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 244 AM EDT TUE AUG 16 2016 VALID AUG 16/0000 UTC THRU AUG 19/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z PRELIMINARY MODEL EVALUATION...INCLUDING THE UKMET AND ECMWF ...PAIR OF WAVES CROSSING THE GREAT LAKES... PREFERENCE: BLEND OF THE GFS/ECMWF/GEFS MEAN CONFIDENCE: AVERAGE FOR THE FIRST WAVE TO SLIGHTLY BELOW AVERAGE FOR THE SECOND WAVE THE MODELS SHOW A PAIR OF MID-UPPER LEVEL WAVES CROSSING THE GREAT LAKES. THE FIRST WAVE IS CROSSING MICHIGAN TONIGHT AND THE MODELS SHOW THE WAVE CROSS NORTHERN NEW YORK/NEW ENGLAND TUE AND TUE NIGHT AND MOVING OFF THE NEW ENGLAND COAST WED...WITH A CLOSED 700 MB CIRCULATION CENTER. THERE ARE TIMING DIFFERENCES WITH THE 21Z SREF MEAN LAGGING BEHIND THE GFS/ECMWF/18Z GEFS MEAN...WHICH CLUSTER BETTER TIMING WISE. THE 00Z NAM IS WITHIN THE CLUSTER TIMING WISE BUT SHOWS A STRONGER/DEEPER 700 MB LOW CROSSING NORTHERN MAINE. A SECOND WAVE CROSSES THE NORTHERN PLAINS TO UPPER MS VALLEY TUE AND INTO THE GREAT LAKES WED. THE 12Z NAM WAS MORE AMPLIFIED THAN OTHER 700 MB HEIGHT FORECASTS BUT HAS REDUCED THE WAVE AMPLITUDE ON THIS 00Z RUN. THE LOWER AMPLITUDE WAVE WAS ASSOCIATED WITH A FASTER PROGRESSION NAM WAVE CROSSING MI FASTER ON WED LOOKS TO BE A LOW PROBABILITY SOLUTION. THE TAIL END OF THE WAVE LOOKS TO BE IN BETTER AGREEMENT IN THE OH VALLEY. THE 18Z-00Z GFS AND GEFS MEAN WERE FLATTER SOLUTIONS SO SIGNIFICANT TIMING/AMPLITUDE DIFFERENCES PERSIST WITH THIS WAVE. ...WEAK MID-LEVEL IMPULSES IMPACTING LOCATIONS FROM CA TO THE GREAT BASIN WITHIN A BROAD UPPER TROUGH... PREFERENCE: BLEND OF THE 00Z NAM/GFS/ECMWF CONFIDENCE: AVERAGE THE MODELS SHOW A BROAD UPPER TROUGH DEVELOPING OVER CA AND THE GREAT BASIN WITH A FEW EMBEDDED SMALLER SCALE CIRCULATIONS. A BROAD 700 MB CIRCULATION PERSISTS OVER CENTRAL CA WITH A FEW EMBEDDED MESOSCALE CIRCULATIONS ROTATING AROUND THE CENTER INTO NV TUE. THE CIRCULATION DRIFTS SOUTH WITH TIME TOWARDS SOUTHERN CA TO THE COAST AROUND 12 THU. GIVEN THE 00Z NAM CLUSTERS WELL WITH OTHER SOLUTIONS...A MODEL CONSENSUS IS PREFERRED. ...AMPLIFYING UPPER TROUGH OVER S-CNTRL CANADA BY THU... WAVY COLD FRONT IMPACTING THE NRN PLAINS THU TO UPPER MS VALLEY AND CENTRAL PLAINS THU NIGHT/FRI MORNING PREFERENCE: BLEND OF THE 00Z GEFS MEAN/12Z UKMET/00Z ECMWF CONFIDENCE: SLIGHTLY BELOW AVERAGE THE MODELS GRADUALLY LOWER HEIGHTS FROM SOUTHERN CANADA INTO THE NORTHERN ROCKIES AND PLAINS...WITH HEIGHT FALLS DRIVING A COLD FRONT EAST ACROSS THE NORTHERN ROCKIES TUE INTO THE NORTHERN PLAINS TO CENTRAL ROCKIES THU TO THE UPPER MS VALLEY AND CENTRAL PLAINS BY 12Z FRI. THE 00Z NAM/GFS WERE HIGHER AMPLITUDE AND SLOWER WITH THE 500 MB TROUGH OVER SOUTHWEST CANADA...WHICH RESULTS IN HIGH PRESSURE SLOWER TO MOVE OUT OUT CANADA INTO MT. THE 00Z ECMWF HAS JOINED THE TREND TOWARDS A HIGHER AMPLITUDE TROUGH AND SLOWER MOVING FRONT IN MT. THE 00Z UKMET HAD A COUNTER TREND MOVE TOWARDS A LOWER AMPLITUDE WAVE...BUT WAS ALONE IN DOING SO. THE MAJORITY TREND IS PREFERRED. FURTHER EAST...WAVES OF LOW PRESSURE MOVE ALONG THE FRONT FROM THE NORTHERN AND CENTRAL PLAINS TO THE UPPER MS VALLEY...WITH EACH MODEL SLIGHTLY DIFFERENT REGARDING LOCATION/TIMING OF WAVE ALONG THE FRONT. THE 00Z GFS DEAMPLIFIED THE 700-500 MB WAVE AND THUS CHANGES THE LOCATION OF LOW PRESSURE AND SPEED OF THE FRONT. AS A RESULT ANY ONE SOLUTION WOULD BE REGARDED AS A POSSIBILITY WITHOUT A FAVORED CLUSTER. A CONSENSUS BASED APPROACH IS RECOMMENDED UNTIL BETTER CLUSTERING DEVELOPS IN FUTURE FORECASTS. ...MID-UPPER LEVEL TROUGH DRIFTING WEST IN THE SRN/CNTRL PLAINS... PREFERENCE: BLEND OF THE 00Z GFS...00Z ECMWF...00Z GEFS MEAN CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS INDICATE A NORTHEAST TO SOUTHWEST TROUGH AXIS EXTENDING ACROSS THE SOUTHERN PLAINS TO A 700 MB FRONT NEAR THE OK/AR BORDER ON TUE AND TUE NIGHT. THE TROUGH AXIS DRIFTS WEST WITH TIME WITH THE WAVE MOVING ACROSS CENTRAL TO WEST TEXAS. THE MS VALLEY TO OK PORTION OF THE TROUGH AXIS WEAKENS WITH TIME AS HEIGHTS BUILDS. CLUSTERING IS A LITTLE BETTER THAN AVERAGE WITH THE 700 MB WAVE DRIFTING WEST ACROSS TEXAS...SUGGESTING A CONSENSUS BASED APPROACH BE USED. THE 00Z NAM SHOWS A CLOSED CIRCULATION CENTER AT 700 MB 00Z FRI NEAR THE TX/NM BORDER...WHICH WILL BE CONSIDERED A LOW PROBABILITY SOLUTION BUT NOT OUT OF THE QUESTION. THE GFS/ECMWF/GEFS MEAN FORM A WELL DEFINED CLUSTER OF SOLUTIONS. PETERSEN www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...