MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
222 AM EDT TUE AUG 25 2009
 
VALID AUG 25/0000 UTC THRU AUG 28/1200 UTC
 

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

00Z MODEL EVALUATION INCLUDING THE NEW ECMWF AND MODEL PREFERENCES

ANY INITIALIZATION ERRORS WITH THE NAM/GFS DO NOT APPEAR TO
SIGNIFICANTLY IMPACT THEIR SOLUTIONS.

...COLD FRONT EXTENDING FROM THE WESTERN GREAT LAKES INTO THE
PLAINS...

PREFERENCE: AFTER 00Z WED...1/2 EACH GFS/ECMWF

THE NAM SHOWS GOOD AGREEMENT WITH OTHER GUIDANCE REGARDING THE
MERGING OF A COLD FRONT EXTENDING FROM MINNESOTA TO NEBRASKA WITH
A SMALLER COLD FRONT OVER WESTERN KANSAS LATER TODAY.
OTHERWISE...THE NAM IS DEEPER...FARTHER NORTH...AND MORE SUSTAINED
WITH A SURFACE LOW OVER IOWA AFTER 00Z WED...RESULTING IN A MORE
NORTHWARD FRONTAL POSITION OVER THE OHIO VALLEY FOR THE REMAINDER
OF THE PERIOD. MEANWHILE...THE GFS/ECMWF ARE IN REASONABLE
AGREEMENT WITH THE FRONTAL POSITION...WITH MULTI-MODEL ENSEMBLE
MEANS INDICATING A BLEND OF BOTH SOLUTIONS IS BEST TO ADDRESS THE
GROWING UNCERTAINTY LATER IN THE PERIOD...ESPECIALLY BY DAY 3. THE
NEW UKMET/CANADIAN ALSO AGREE WITH THE PREFERENCE.  

...COLD FRONT NEAR THE PACIFIC NORTHWEST...

PREFERENCE: AFTER 12Z THU...1/2 EACH GFS/ECMWF

THE NAM IS SIMILAR TO OTHER GUIDANCE THROUGH WED NGT...BY WHICH
TIME THE NAM MOVES TOWARD THE FAST SIDE OF THE GUIDANCE ENVELOPE
WITH THE FRONT PASSING THROUGH THE NORTHERN PLAINS/UPPER
MIDWEST...AND BECOMES WEAKER ALOFT THAN MOST GUIDANCE. THE
GFS/ECMWF ARE CLOSE TO MULTI-MODEL ENSEMBLE MEANS WITH A BLEND OF
THE TWO SOLUTION RECOMMENDED TO ADDRESS SOME OF THE UNCERTAINTY
WITH THE POSITION. THE SAME HOLDS TRUE WITH THE INTENSITY...WITH A
BLENDING OF THE STRONGER ECMWF...WHICH IS WITHIN THE STRONGER HALF
OF THE SOLUTION ENVELOPE...WITH THE GFS WHICH IS NEAR THE
CONSENSUS. 

...UPPER LOW FORMING OVER MISSISSIPPI/ALABAMA...

PREFERENCE: GEFS MEAN

THE NEW UKMET HAS ADDED SOME EASTWARD SPEED TO THE UPPER LOW BY
THE END OF THE PERIOD...THUS INCREASING THE SOLUTION
SPREAD...WHILE THE NEW GEFS MEAN IS SIMLAR TO ITS PREVIOUS RUN
ALONG WITH THE ECMWF ENSEMBLE MEAN. GIVEN SOME UNCERTAINTY WITH
HOW THE UPSTREAM FLOW MAY INTERACT WITH THE UPPER LOW TOWARD THE
END OF THE PERIOD...PREFER THE NEW GEFS MEAN.

...TROPICAL WAVE NEARING THE BAHAMAS THU/FRI...

PREFERENCE: ECMWF/CANADIAN/NOGAPS/ECMWF ENSEMBLE MEAN

IN CONSIDERING GLOBAL GUIDANCE...THE GFS LIES NEAR THE NORTHEAST
SIDE OF THE GUIDANCE ENVELOPE BY 12Z FRI...NAM WITHIN THE NORTHERN
HALF...AND ECMWF/CANADIAN/NOGAPS/ECMWF ENSEMBLE MEAN NEAR THE
CONSENSUS. GIVEN THAT THE NAM/GFS ARE IN THE MINORITY WITH A
MID/UPPER LEVEL WEAKNESS LINGERING ALONG THE EAST COAST...PREFER
THE MORE SOUTHWARD CONSENSUS FOR THE TRACK BY 12Z FRI. THE NEW
CANADIAN CONTINUES AS A DEEP OUTLIER...AND THUS IS DISCOUNTED
UNTIL THE WAVE SHOWS SIGNS OF BETTER ORGANIZATION.

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

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

JAMES