MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
223 AM EDT WED MAY 06 2009
 
VALID MAY 06/0000 UTC THRU MAY 09/1200 UTC
 

...SEE NOUS42 KWNO ADMNFD FOR THE STATUS OF THE UPPER AIR
INGEST...

00Z FINAL MODEL EVALUATION INCLUDING THE NEW ECMWF AND MODEL
PREFERENCES

ANY INITIALIZATION ERRORS WITH THE NAM/GFS ARE DESCRIBED UNDER THE
RELEVANT SYSTEM HEADINGS.

...SHORTWAVE TROUGH OVER THE MID-ATLANTIC...

MODEL PREFERENCE: 60 PERCENT GFS TO 40 PERCENT ECMWF

UPPER LEVEL MODEL DIAGNOSTICS COMPARED WITH WATER VAPOR
IMAGERY/RADAR LOOPS SUGGEST THAT THIS TROUGH IS SUBSTANTIALLY
FARTHER NORTHEAST AND POSSIBLY STRONGER THAN INITIALIZED BY THE
NAM. THE INCLUSION OF ADDITIONAL SATELLITE RADIANCES APPEARS TO
SIGNIFICANTLY IMPROVE ITS DEPICTION IN THE GFS. HOWEVER RADAR
TRENDS SHOW PRECIPITATION ALREADY FARTHER NORTH ACROSS THE
NORTHEAST THROUGH THE 03Z THAN FORECAST BY THE GFS.

IN TERMS OF THE FORECAST...THE NAM IS CONSIDERED LEAST LIKELY
GIVEN THE INITIALIZATION CONCERNS MENTIONED ABOVE. THE GFS/ECMWF
DEPICT SIMILAR INFLUENCES AS THE TROUGH ACCELERATES THROUGH THE
NORTHEAST LATER TODAY...WITH THE ECMWF SLIGHTLY STRONGER NEAR THE
COAST THAN THE GFS...BUT NOT UNREASONABLY SO GIVEN RADAR/SATELLITE
TRENDS. THE NEW UKMET/CANADIAN SUPPORT A NON-NAM SOLUTION AS WELL.


...SHORTWAVE TROUGH OVER THE SOUTHERN PLAINS...

MODEL PREFERENCE: 1/3 EACH ECMWF/UKMET/CANADIAN

THE NAM'S DEPICTION OF MID LEVEL ASCENT GENERALLY LIES NEAR THE
NORTH TO WEST SIDES OF THE GUIDANCE ENVELOPE THROUGH THE
PERIOD...WITH CURRENT TRENDS SUGGESTING IT'S EARLY FORECAST
VERTICAL MOTION PROFILE IS SHIFTED TOO FAR NORTH INTO MISSOURI.
MEANWHILE...THE GFS FOCUSES ITS MAXIMUM ASCENT WITHIN WHAT APPEARS
TO BE A CONVECTIVELY-INDUCED MID-LEVEL VORTICITY MAXIMA THAT
REACHES SOUTHERN OHIO BY 18Z TODAY...WHICH THEN HELPS THE TROUGH
TO MOVE FASTER THROUGH THE NORTHEAST. THE NEW UKMET/CANADIAN ARE
CLOSEST TO THE SLOWER ECMWF...WHICH IS CONSISTENT WITH MOST MODEL
TRENDS.

...CYCLONE OVER SOUTHERN ALBERTA...

MODEL PREFERENCE: ECMWF OR UKMET

THE MODELS ARE QUITE CLOSE THROUGH 00Z FRI...WHEN THE GFS BEGINS
TO MOVE TOWARD THE FAST SIDE OF THE TOTAL GUIDANCE ENVELOPE.
MEANWHILE...THE NAM/ECMWF/UKMET ARE IN GOOD AGREEMENT THROUGH THE
PERIOD....WITH REASONABLE SUPPORT FROM GEFS/ECMWF ENSEMBLES.

...UPPER LOW PROGRESSING FROM THE PACIFIC NORTHWEST INTO THE
PLAINS THROUGH FRIDAY...

MODEL PREFERENCE: 1/3 EACH NAM/ECMWF/GEFS OR ECMWF ENSEMBLE MEAN

THE MODELS INDICATE SIMILAR TIMING AND STRENGTH OF A SHORTWAVE
TROUGH REACHING THE PACIFIC NORTHWEST THIS MORNING BEFORE MOVING
INLAND...WHILE ALSO INDICATING SIMILAR STRENGTH/TIMING OF THE
WEAKENING UPPER LOW CROSSING THE NORTHERN ROCKIES.
HOWEVER...BEGINNING 12Z SAT...THE GFS MOVES TOWARD THE STRONG SIDE
OF THE GUIDANCE...WHILE THE NAM/NEW ECMWF HOVER NEAR THE
DETERMINISTIC AND ENSEMBLE MEANS. RECOMMEND A CONSENSUS APPROACH
BY 72-84 HRS DUE TO INCREASING MODEL SPREAD/UNCERTAINTY.

...MODEL TREND GRAPHICS AT
WWW.HPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML...

...500 MB FORECASTS AT WWW.HPC.NCEP.NOAA.GOV/H5PREF.SHTML...

JAMES