516
FXUS10 KWNH 141736
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
136 PM EDT THU AUG 14 2008
VALID AUG 14/1200 UTC THRU AUG 18/0000 UTC
MODEL INITIALIZATION...
..SEE NOUS42 KWNO ADMNFD FOR STATUS OF UPPER AIR INGEST
TROPICAL LOW MOVING THROUGH THE BAHAMAS SUNDAY...
THE TROPICAL LOW IS NEAR THE SOUTHEAST EDGE OF THE MODEL
DOMAIN...AND THE NOAA
DROPSONDES RELEASED IN VICINITY OF THE LOW THIS MORNING WERE
BEFORE NAM INITIALIZATION. THEREFORE...INITIALIZATION ERRORS COULD
BECOME AN ISSUE. OTHERWISE...ANY
INITIALIZATION ERRORS WITH THE NAM DO NOT APPEAR TO NEGATIVELY
IMPACT ITS SHORT RANGE FORECAST.
MODEL TRENDS...
VIGOROUS SHORTWAVE TROUGH OFF THE NORTHEAST COAST...
THE 12Z NAM IS A FEW MILLIBARS WEAKER WITH THE CENTRAL PRESSURE OF
THE SURFACE LOW...
AND SEVERAL HOURS FASTER THROUGH THE NEXT 24 HRS BEFORE LEAVING
THE AREA. THE 12Z GFS HAS ALSO TRENDED SLIGHTLY FASTER WITH THE
SURFACE LOW.
SHORTWAVE TROUGH OVER THE NORTHERN GREAT LAKES...
THE 12Z NAM HAS TRENDED SLOWER AFTER 16/12Z COMPARED TO THE NAM 12
HRS PREVIOUS. THE 12Z GFS HAS TRENDED SLOWER WITH GREATER
AMPLITUDE DEVELOPING AFTER 16/12Z.
SHORTWAVE TROUGH EXTENDING ACROSS THE SOUTHEAST...
THE NAM AND GFS SHOW GOOD RUN-TO-RUN CONTINUITY.
TROPICAL LOW MOVING THROUGH THE BAHAMAS SUNDAY...
THE 12Z NAM SHOWS GOOD OVERALL CONTINUITY WITH THE 00Z NAM.
HOWEVER...THE LATEST NAM IS SLIGHTLY FARTHER NORTH WITH THE
TROPICAL LOW AS IT MOVES THROUGH THE BAHAMAS. REFERENCE THE
INITIALIZATION SECTION ABOVE FOR MORE INFORMATION ABOUT THE 12Z
NAM. THE 12Z GFS HAS TRENDED SLIGHTLY FARTHER SOUTH BUT LIKE
EARLIER RUNS MAINTAINS A WEAK CIRCULATION.
COMPACT SHORTWAVE TROUGH OVER KANSAS...
THE 12Z NAM/GFS ARE CONSIDERABLY STRONGER WITH THIS TROUGH WHILE
PROGRESSING IT THROUGH THE SOUTHEAST ON FRIDAY. THE 00Z NAM/GFS
DEPICTED A MUCH WEAKER SHORTWAVE TROUGH BY 14/12Z AND WEAKENED IT
ENTIRELY BEFORE REACHING THE SOUTHEAST.
UPPER LOW REACHING THE CENTRAL ROCKIES BY DAYS 2/3...
THE NAM HAS TRENDED FARTHER SOUTH AND SLIGHTLY MORE COMPACT WITH
THE LOW. THE 12Z GFS HAS GOOD CONTINUITY WITH ITS RUN 12 HRS
PRIOR.
HIGH AMPLITUDE TROUGH REACHING THE PACIFIC NORTHWEST DAYS 2/3...
PHASE SPEED IS GOOD OVER THE LAST 12 HRS OF NAM RUNS.
HOWEVER...THE 12Z NAM IS SLIGHTLY DEEPER WITH THE TROUGH BY DAY 3.
THE 12Z GFS HAS GOOD CONTINUITY.
...MODEL TREND GRAPHICS AT
WWW.HPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML...
MODEL DIFFERENCES AND PREFERENCES...
VIGOROUS SHORTWAVE TROUGH OFF THE NORTHEAST COAST...
THE 12Z DETERMINISTIC GUIDANCE HAS CLUSTERED AROUND A WEAKER AND
FASTER SOLUTION THROUGH THE NEXT 24-36 HRS...WHICH HAS BEEN
CONSISTENTLY DEPICTED BY THE GFS. GIVEN GOOD PERFORMANCE OF THE
GFS...AND THAT THE GFS IS NEAR THE CENTER OF THE CURRENT GUIDANCE
SPREAD...BELIEVE A GFS SOLUTION IS BEST.
SHORTWAVE TROUGH OVER THE NORTHERN GREAT LAKES...
MODEL SPREAD REMAINS SMALL THROUGH 15/12Z...BEFORE THE ECMWF
BECOMES AN OUTLIER BY PROGRESSING THE TROUGH MORE RAPIDLY THAN
OTHER GUIDANCE. PREFER A BLEND OF THE NAM/GFS...WHICH IS ALSO
CONSISTENT WITH THE MODEL CHOICE FOR SOUTHERN PORTIONS OF AN
AMPLIFYING TROUGH ACROSS THE SOUTHEAST BY DAY 3.
SHORTWAVE TROUGH EXTENDING ACROSS THE SOUTHEAST...
GOOD AGREEMENT EXISTS THAT THE TROUGH ACROSS GEORGIA/ALABAMA WILL
PROGRESS QUICKLY OFFSHORE THROUGH THE NEXT 12-24 HRS.
TROPICAL LOW MOVING THROUGH THE BAHAMAS SUNDAY...
GUIDANCE SPREAD INCREASES CONSIDERABLY BY DAY 3 WITH THE TPC
FORECAST LEFT OF THE NAM...AND CONSIDERABLY RIGHT OF THE
CANADIAN/UKMET/ECWMF. THE OFFICIAL FORECAST IS CLOSE TO THE MEAN
OF THESE SOLUTIONS...WHICH IS ALSO CLOSE TO THE GFS. ALTHOUGH THE
GFS APPEARS TO UNDERESTIMATE ITS INTENSITY.
COMPACT SHORTWAVE TROUGH OVER KANSAS...
GIVEN THE MODEL TRENDS DESCRIBED ABOVE AND THEIR GOOD AGREEMENT
WITH THE TROUGH'S PROGRESS THROUGH THE SOUTHEAST BY DAY 3...PREFER
A BLEND OF THE NAM/GFS FOR THE GENERAL EVOLUTION OF THE TROUGH.
HOWEVER..CONFIDENCE IS LOW IN THE GFS DEPICTION OF NUMEROUS QPF
MAXIMA OVER PARTS OF THE HIGH PLAINS...SOUTHERN PLAINS...AND
NORTHERN GULF COAST. OLDER MODEL GUIDANCE...INCLUDING THE 00Z
ECMWF...HAS NOT PERFORMED WELL WITH THE HANDLING OF THIS TROUGH
THROUGH 14/12Z...AND THUS THE ECMWF HAS NOT BEEN USED FOR THIS
DISTURBANCE.
UPPER LOW REACHING THE CENTRAL ROCKIES BY DAYS 2/3...
THE NAM/GFS HAVE COME INTO AGREEMENT WITH THE CURRENT AND PREVIOUS
ECWMF...WITH THE LOW DRIFTING INTO COLORADO BY DAYS 2/3.
UNCERTAINTY INCREASES CONSIDERABLY BY 17/00Z...WHEN SEVERAL OF THE
GFS ENSEMBLE MEMBERS HAVE THE LOW DRIFTING INTO KANSAS. GIVEN THAT
SO FEW MEMBERS SHOW THIS EASTWARD PROGRESSION...BELIEVE MORE OF AN
ECMWF AND ECMWF ENSEMBLE MEAN BLEND IS BEST.
HIGH AMPLITUDE TROUGH REACHING THE PACIFIC NORTHWEST DAYS 2/3...
THE ECMWF BECOMES AN OUTLIER BY 17/00Z WITH THE TROUGH ENTERING
THE WEST COAST SLOWER AND STRONGER THAN OTHER GUIDANCE. PREFER A
BLEND OF THE GFS WITH THE 00Z GFS ENSEMBLE MEAN THAT MAINTAIN A
MORE PROGRESSIVE TROUGH AFFECTING THE WEST COAST...WHICH IS ALSO
MORE IN LINE WITH THE NAM.
500 MB FORECASTS AT
WWW.HPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML...
JAMES
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