Prognostic Meteorological Discussion
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FXUS10 KWNH 010427
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1226 AM EDT TUE SEP 01 2015

VALID SEP 01/0000 UTC THRU SEP 04/1200 UTC

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

00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES

UPPER TROUGH FORMING ACROSS THE PACIFIC NORTHWEST...

PREFERENCE: GFS OR ECMWF
CONFIDENCE: ABOVE AVERAGE

THE GFS AND 12Z ECMWF ALIGN WELL WITH THE MODEL CONSENSUS
INCLUDING THE ENSEMBLE MEANS WITH NEAR TO BELOW NORMAL SPREAD BY
DAY 3...WITH THE NAM TRENDING FASTER BUT STILL LAGGING THE
CONSENSUS...
WHICH COULD BE A RESULT ITS OCCASIONAL SLOW BIAS.
THUS...RECOMMEND EITHER THE GFS OR ECMWF.

UPPER LOW OVER THE LOWER MS VALLEY...

PREFERENCE: HALFWAY BETWEEN THE GFS AND 12Z ECMWF
CONFIDENCE: BELOW AVERAGE

THE SPREAD REMAINS VERY HIGH CONCERNING THE DETAILS OF THE
STRUCTURE OF THE EVOLVING LOW.  HOWEVER...THERE ARE SOME
INDICATIONS TO LEAN SOMEWHERE BETWEEN THE GFS AND 12Z
ECMWF....WITH THE NAM TRENDING EAST AND AWAY FROM ITS MOST
WESTWARD POSITION NEAR THE TEXAS COAST BY DAY 3...THE GFS TRENDING
EASTWARD...AND THE 18Z PARALLEL GEFS MEAN SUPPORTING AN
INTERMEDIATE SOLUTION BETWEEN THE 18Z OPERATIONAL GEFS MEAN AND
THE 12Z ECMWF ENSEMBLE MEAN.  THUS...A SOLUTION ABOUT MIDWAY
BETWEEN THE GFS AND 12Z ECMWF IS PREFERRED.

REMNANTS OF ERIKA...

PREFERENCE: GFS
CONFIDENCE: AVERAGE

THE GFS ALIGNS BEST WITH THE REMNANTS OF ERIKA...WITH THE NAM A
CLOSE SECOND AND THE 12Z ECMWF ALREADY TOO FAR NORTHEAST.
THUS...THE ECMWF CAN BE RULED OUT.  BETWEEN THE GFS AND NAM...THE
GFS APPEARS TO BETTER CAPTURE THE SUBSIDENCE RING DEVELOPING OVER
SOUTHERN FLORIDA PARTICULARLY THROUGH TODAY AND TONIGHT.
THUS...RECOMMEND THE GFS.

SHORTWAVE PATTERN ACROSS THE GREAT LAKES/OH VALLEY THU-FRI...

PREFERENCE: ENSEMBLE MEANS
CONFIDENCE: BELOW AVERAGE

THE GFS AND 12Z ECMWF REPRESENT THE OUTER EDGES OF THE
GUIDANCE...WITH THE GFS POSSIBLY TOO QUICK TO PROGRESS A SHORTWAVE
TROUGH INTO A LONGWAVE RIDGE OVER CENTRAL CANADA BY DAY 3...THUS
BUILDING THE SHORTWAVE RIDGE ACROSS THE GREAT LAKES...WHILE THE
12Z ECMWF IS NEAR THE STRONG EDGE OF THE GUIDANCE WITH A SHORTWAVE
TROUGH EXITING THE ROCKIES AND REACHING THE CENTRAL PLAINS.  THE
NAM IN BETWEEN THESE MORE EXTREME SOLUTIONS BUT HAS ITS OWN ISSUES
WITH A SUSPICIOUSLY STRONG AND NORTHERN LEE LOW DEVELOPING OVER
THE NORTHERN PLAINS...THUS POSSIBLY IMPACTING TEMPS/WINDS OVER THE
UPPER MIDWEST.  THUS...THE NAM IS NOT RECOMMENDED EITHER.  TO
ADDRESS THESE CONCERNS...
RECOMMEND THE ENSEMBLE MEANS UNTIL BETTER DETERMINISTIC AGREEMENT
DEVELOPS.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

JAMES

$$





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