Prognostic Meteorological Discussion
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000
FXUS10 KWNH 271605
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1204 PM EDT WED MAY 27 2015

VALID MAY 27/1200 UTC THRU MAY 31/0000 UTC

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

12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES

SHORTWAVE TROUGH OVER THE UPPER MIDWEST...

MODELS SHOW GOOD LARGE-SCALE AGREEMENT.

SHORTWAVE TROUGH OVER THE LOWER MS VALLEY...

PREFERENCE: BEFORE 00Z THU...HRRR/RAP
             AFTER 00Z THU...RAP/NAM/GFS
CONFIDENCE: BELOW AVERAGE

THE NAM AND GFS SUFFER FROM SIGNIFICANT SPIN UP ERROR WITH THE MCS
OVER THE LOWER MS VALLEY.  IN ADDITION TO DEPICTING LESS RAINFALL
EARLY IN THE PERIOD IN ASSOCIATION WITH THE MCS...THE
GFS 2M INITIALIZATION DEWPOINTS ACROSS MOST OF NORTHERN TEXAS ARE
5 TO 10 DEGREE F TOO HIGH...WHICH IS LIKELY CONTRIBUTING TO TOO
HIGH CAPE/LOW CIN FIELDS RESPECTIVELY EARLY IN THE FORECAST CYCLE.
 THE 00Z ECMWF IS ALSO TOO WEAK AND SLOW WITH THE TROUGH COMPARED
WITH OBS.  MEANWHILE...THE HRRR/RAP ARE CLOSEST TO THE OBS AND MAY
BE THE MOST USEFUL EARLY IN PERIOD.  AFTER THE END TIMES OF THE
HRRR/RAP...RECOMMEND MERGING THEIR SOLUTIONS WITH THE NAM/GFS
WHICH ARE THE BEST AVAILABLE BUT STILL TOO WEAK IN MOST CASES.

SHORTWAVE TROUGH NEAR THE CO/KS BORDER...

PREFERENCE: GFS
CONFIDENCE: ABOVE AVERAGE

THE GFS ALIGNS BEST WITH SATELLITE IMAGERY AT INITIALIZATION WITH
THE NAM A CLOSE SECOND AND THE 00Z ECMWF TOO WEAK AND WEST OF THE
IMAGERY.  GIVEN THAT THE GFS IS CLOSEST AND GIVEN A WIDER DATA
ASSIMILATION WINDOW COMPARED TO THE NAM...RECOMMEND THE GFS.

CLOSED LOW OVER THE PACIFIC NORTHWEST...
COLD FRONT CROSSING THE PLAINS/MS VALLEY FRI...

PREFERENCE: EQUAL BLEND GFS/ECMWF
CONFIDENCE: AVERAGE

THE NAM MOVES STEADILY TOWARD THE FAST AND DEEP SIDES OF THE
GUIDANCE ALOFT THUS INFLUENCING ITS FRONTAL TIMING...WHILE THE
GFS/ECMWF SHOW GOOD AGREEMENT WITH EACH OTHER WHILE DISPLAYING
SOME TYPICAL STRENGTH/TIMING DIFFERENCES.  GIVEN ADDITIONAL
SUPPORT FROM THE 00Z UKMET/CANADIAN AS WELL AS THE ENSEMBLE
MEANS...RECOMMEND DISCOUNTING THE NAM IN FAVOR OF A GFS/ECMWF
BLEND.

CLOSED LOW REACHING SOUTHWEST CANADA SATURDAY...

PREFERENCE: GFS OR ECMWF
CONFIDENCE: AVERAGE

THE NAM BECOMES SLOWER THAN THE MAJORITY OF GUIDANCE...WHILE THE
GFS/ECMWF SHOW GOOD AGREEMENT WITH EACH OTHER.  THUS...RECOMMEND
EITHER THE GFS OR ECMWF.

...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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