899
FXUS10 KWNH 240546
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
145 AM EDT SUN AUG 24 2008
VALID AUG 24/0000 UTC THRU AUG 27/1200 UTC
MODEL INITIALIZATION...
..SEE NOUS42 KWNO ADMNFD FOR STATUS OF UPPER AIR INGEST
..TROPICAL DEPRESSION FAY
OBSERVED SURFACE PRESSURES NEAR THE CENTER OF FAY AVERAGED 2-4 MB
LOWER THAN THE 00 HR FORECAST FROM THE NAM. ADDITIONALLY...00Z
RAOB DATA FROM KJAN/KBMX/KFFC/KTLH SHOW A GENERALLY COOLER LOW/MID
TROPOSPHERE THAN DEPICTED BY THE 00Z NAM...WITH OBSERVED 500 MB
HEIGHT VALUES AVERAGING 30 METERS LESS THAN THE MODEL.
OTHERWISE...ANY INITIALIZATION ERRORS WITH THE NAM AND GFS DO NOT
APPEAR TO SIGNIFICANTLY IMPACT THEIR FORECASTS.
MODEL TRENDS...
..TROPICAL DEPRESSION FAY
THE NAM IS CONSISTENT WITH PREVIOUS NAM RUNS IN MOVING FAY
WESTWARD THROUGH 25/12Z. HOWEVER THE 00Z NAM IS FASTER WITH MOVING
FAY NORTHEASTWARD AFTER 26/00Z. THE GFS HAS RECENTLY BEEN
CONSISTENT WITH THE PATH OF FAY.
..UPPER TROUGH CENTERED OVER ONTARIO CANADA
THE NAM IS CONSISTENT WITH PREVIOUS RUNS. THE 00Z GFS IS SLIGHTLY
WEAKER WITH THE TROUGH AS IT REACHES MAINE BY 26/12Z COMPARED TO
EARLIER GFS RUNS.
..UPPER LOW OFFSHORE OF NORTH CAROLINA
THE 00Z NAMS LIFTS THIS LOW TO THE NORTHEAST FASTER THAN PREVIOUS
NAM RUNS. THE 00Z GFS IS SIMILAR TO PAST RUNS.
..UPPER TROUGH MOVING INTO THE PACIFIC NORTHWEST
THE 00Z NAM IS A LITTLE SLOWER WITH THE EASTWARD PROGRESSION OF
THIS TROUGH AFTER 26/00Z COMPARED TO EARLIER NAM RUNS. THE 00Z GFS
IS SLOWER WITH A SHORTWAVE TROUGH REACHING THE COAST OF BRITISH
COLUMBIA BY 27/00Z COMPARED TO EARLIER GFS RUNS. OTHERWISE...THE
00Z GFS SHOWS GOOD CONTINUITY WITH THE MAIN TROUGH OVER THE
PACIFIC NORTHWEST.
..UPPER LOW NEAR EL PASO
THE 00Z NAM AND GFS ARE CONSISTENT WITH PREVIOUS RUNS IN ALLOWING
THE UPPER LOW TO WEAKEN WHILE DRIFTING WESTWARD.
...MODEL TREND GRAPHICS AT
WWW.HPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML...
MODEL DIFFERENCES AND PREFERENCES...
..TROPICAL DEPRESSION FAY
OTHER THAN SEVERAL VERSIONS OF THE BAM MODEL...NUMERICAL GUIDANCE
CLOSELY AGREES THAT FAY WILL MOVE SLOWLY WEST...THEN SOUTHWEST
INTO SOUTHERN LOUISIANA BY 25/12Z...BEFORE SLOWING DOWN AND
PERHAPS MEANDERING WITHIN VERY WEAK FLOW ALOFT THROUGH THE
REMAINDER OF THE SHORT RANGE PERIOD. THE NAM HAS BEEN DISCOUNTED
HOWEVER...DUE TO INITIALIZATION CONCERNS AND SOME RUN-TO-RUN
INCONSISTENCY WITH ITS PATH. THE GFS/ECWMF ARE CLOSEST TO THE
LATEST TPC FORECAST AND ARE RECOMMENDED AS A FIRST GUESS FOR THE
POSITION OF FAY THROUGH DAY 3.
..UPPER TROUGH CENTERED OVER ONTARIO CANADA
..UPPER TROUGH MOVING INTO THE PACIFIC NORTHWEST
GOOD AGREEMENT EXISTS THROUGH 48 HRS...BEFORE THE NAM BECOMES THE
MOST PROGRESSIVE WITH BOTH TROUGHS...WHILE THE GFS/12Z ECWMF HAVE
COME INTO BETTER AGREEMENT THAT THE TROUGHS WILL TRAVEL SLOWER AND
REMAIN MORE AMPLIFIED. GFS/ECMWF ENSEMBLES CONTINUE TO SHOW
CONSIDERABLE SPREAD DEVELOPING IN THE 500 MB HEIGHTS AND PMSL
FIELDS OVER THE PACIFIC NORTHWEST BY DAY 3. PREFER A BLEND OF THE
DETERMINISTIC GFS/ECMWF WITH THEIR ENSEMBLE MEANS BY THIS TIME TO
HELP MAINTAIN AMPLITUDE BUT YET INCORPORATE UNCERTAINTY.
..UPPER LOW OFFSHORE OF NORTH CAROLINA
GOOD MODEL AGREEMENT EXISTS THAT THIS LOW WILL BE LIFTED TOWARD
THE NORTHEAST BY AN APPROACHING SHORTWAVE TROUGH...WITH THE LOW
REMAINING OFFSHORE.
..UPPER LOW NEAR EL PASO
GOOD MODEL CONTINUITY EXISTS THAT THE LOW WILL WEAKEN WHILE
DRIFTING WESTWARD THROUGH THE PERIOD.
500 MB FORECASTS AT
WWW...NCEP.HPC.NOAA.GOV/H5PREF/H5PREF.SHTML...
JAMES
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