Prognostic Meteorological Discussion
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FXUS10 KWNH 020623
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
222 AM EDT SUN AUG 02 2015

VALID AUG 02/0000 UTC THRU AUG 05/1200 UTC

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

00Z NAM/GFS EVALUATION INCLUDING THE UKMET/CANADIAN AND
PREFERENCES

SHORTWAVE TROUGH OVER NEVADA...

PREFERENCE: EQUAL BLEND GFS/ECMWF
CONFIDENCE: AVERAGE

THE NAM MOVES TOWARD THE STRONG EDGE OF THE GUIDANCE AFTER
REACHING THE PLAINS TUESDAY NIGHT BUT OTHERWISE SHOWS REASONABLY
GOOD AGREEMENT WITH THE GFS/ECMWF AND THE ENSEMBLE MEANS.  DUE TO
BETTER OVERALL AGREEMENT AND CONTINUITY HOWEVER...RECOMMEND MORE
EMPHASIS UPON THE GFS/ECMWF.

SHORTWAVE TROUGH OVER S. COLORADO...

PREFERENCE: BEFORE 12Z TUE...BLEND GFS/ECMWF
             AFTER 12Z TUE...BLEND OF THE ENSEMBLE MEANS
CONFIDENCE: BELOW AVERAGE

THE NAM QUICKLY BECOMES A STRONG OUTLIER OVER THE PLAINS AND THUS
IS DISCOUNTED...WHEREAS THE GFS/ECMWF SHOW REASONABLY GOOD
AGREEMENT WITH EACH OTHER THROUGH DAY 2 BEFORE SHOWING LARGER
DIFFERENCES AS THE SOLUTION ENVELOPE QUICKLY WIDENS BY DAY 3.  DUE
TO THESE GROWING UNCERTAINTIES...RECOMMEND SWITCHING TO THE
ENSEMBLE MEANS BY DAY 3...TO MORE ACCURATELY ACCOUNT FOR THE
HIGHER UNCERTAINTY.

COLD FRONT OVER MONTANA...

PREFERENCE: EQUAL BLEND GFS/ECMWF
CONFIDENCE: AVERAGE

THE NAM BECOMES SLOWER WITH THE FRONT AND STRONGEST WITH THE
SURFACE LOW CROSSING THE GREAT LAKES...WITH THE DEPTH OF THE LOW
CHARACTERISTIC OF CONVECTIVE GRID-SCALE FEEDBACK.  THUS...
RECOMMEND DISCOUNTING THE NAM.  OTHERWISE...THE GFS/ECMWF SHOW
GOOD AGREEMENT THROUGH THE PERIOD...WITH AN EQUAL BLEND OF THE TWO
RECOMMENDED TO RESOLVE ANY LINGERING SMALL SCALE DIFFERENCES.

LOW PRESSURE OVER THE NORTHEAST GULF OF MEXICO...

PREFERENCE: EQUAL BLEND GFS/ECMWF
CONFIDENCE: AVERAGE

THE NAM QUICKLY BECOMES A FAST OUTLIER WITH THE LOW AND THUS IS
DISCOUNTED...WHILE THE GFS/ECMWF SHOW REASONABLY GOOD AGREEMENT
WITH EACH OTHER AND ARE BEST SUPPORTED BY THE ENSEMBLE MEMBERS.
THUS...RECOMMEND AN EQUAL BLEND OF THE TWO TO RESOLVE ANY
LINGERING SMALL SCALE DIFFERENCES.

CLOSED LOW NEAR THE PACIFIC NORTHWEST MONDAY NIGHT/TUESDAY...

PREFERENCE: NAM OR GFS OR ECMWF
CONFIDENCE: AVERAGE

OTHER THAN THE CANADIAN WHICH IS SLOWER...MODELS SHOW GOOD
AGREEMENT.

...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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