Prognostic Meteorological Discussion
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FXUS10 KWNH 310429
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1228 AM EDT FRI JUL 31 2015

VALID JUL 31/0000 UTC THRU AUG 03/1200 UTC

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

00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES

UPPER HIGH EXTENDING FROM OREGON INTO TEXAS...
SHORTWAVE TROUGH INFLUENCING THE GREAT BASIN/N. ROCKIES THIS
WEEKEND...

PREFERENCE:  3/4 GFS TO 1/4 ECMWF
CONFIDENCE:  BELOW AVERAGE

MODELS SHOW STRONG AGREEMENT IN MAINTAINING THE HIGH OVER TEXAS
THROUGH THE WEEKEND WITH ITS ASSOCIATED SHORTWAVE RIDGE EXTENDING
INTO OREGON...BUT BEGINNING TO ERODE ALONG ITS WESTERN EDGES BY
LATE SATURDAY.  850 MB TEMPERATURE ANOMALIES OF ABOUT 2.5 TO 3
STANDARD DEVIATIONS ABOVE NORMAL SEEM LIKELY TO PERSIST ACROSS THE
PACIFIC NORTHWEST THROUGH THIS PERIOD...HELPING TO PERPETUATE THE
EXCESSIVE HEAT CONDITIONS ACROSS SOME AREAS.

BY EARLY SUNDAY...MODELS REMAIN CONSISTENT IN MERGING OR
CONSOLIDATING 2 OR MORE SHORTWAVE TROUGHS OVER THE SOUTHWEST AND
PROGRESSING THEM ACROSS THE GREAT BASIN AND EVENTUALLY INTO THE
NORTHERN ROCKIES.  WHILE THESE SOLUTIONS INVOLVE THE INTERACTIONS
OF NUMEROUS SHORT WAVELENGTH ELEMENTS INCLUDING THE INFLUENCE OF
CONVECTION THAT MAY RESULT IN DIFFERENT OUTCOMES IN FUTURE
CYCLES...THEY APPEAR REASONABLE...AND SHOULD ALLOW FOR MORE CLOUD
COVER AND SOME PRECIPITATION TO EVENTUALLY SPREAD NORTHWARD INTO
THE REGION.

REGARDING MODEL CHOICES...THE GFS IS CLOSEST TO THE ENSEMBLE MEANS
FOR THE LONGWAVE PATTERN ACROSS THE WEST INCLUDING THE CLOSED LOW
APPROACHING THE PACIFIC NORTHWEST...WITH THE ECMWF WITHIN THE
SLOWER ONE QUARTER OF ALL SOLUTIONS FOR THE CLOSED LOW.
MEANWHILE...THE NAM MOVES GRADUALLY TOWARD THE OUTER EDGES OF THE
GUIDANCE IN MANY PARTS OF THE WEST...AND SO ITS SOLUTIONS IS
ASSOCIATED WITH DECREASING CONFIDENCE BY DAYS 2 AND
3...PARTICULARLY COMPARED WITH OTHER LARGE-SCALE SOLUTIONS.

UPPER TROUGH EXTENDING FROM THE GREAT LAKES SOUTHWARD...
FRONTAL BOUNDARY OVER THE SOUTHEAST...

PREFERENCE: GFS OR ECMWF
CONFIDENCE: ABOVE AVERAGE

OTHER THAN THE NAM BECOMING A STRONG OUTLIER WITH LOW PRESSURE
NEAR OR ALONG THE FRONT OFF THE SOUTHEAST COAST...MODELS SHOW GOOD
LARGE-SCALE AGREEMENT WITH A LARGE TROUGH PERPETUATING SOUTHWARD
FROM THE GREAT LAKES WITH LESS AMPLITUDE THAN SHOWN BY THE
NAM...WITH A GFS OR ECMWF SOLUTION PREFERRED OVERALL.  ACROSS THE
GREAT LAKES HOWEVER...THE GFS SHOWS INDICATIONS OF GRID-SCALE
FEEDBACK SUNDAY NIGHT AND SO RECOMMEND MORE OF THE ECMWF DURING
THIS TIME.

CLOSED LOW NEARING THE PACIFIC NORTHWEST SUNDAY NIGHT...

PREFERENCE: GFS
CONFIDENCE: ABOVE AVERAGE

THE NAM APPEARS TOO QUICK TO ERODE HEIGHTS ACROSS THE REGION AS
EARLY AS 12Z SUNDAY...WHILE THE MAJORITY OF OTHER SOLUTIONS ARE
MUCH SLOWER.  AMONG THE REMAINING SOLUTIONS...THE GFS IS CLOSEST
TO THE ENSEMBLE MEANS BY 84 HRS...WITH THE OPERATIONAL 12Z ECMWF
SLOWER THAN ITS ENSEMBLE MEAN.  THE OVERALL SPREAD IS ABOUT
AVERAGE.  GIVEN BETTER OVERALL SUPPORT FOR THE GFS...RECOMMEND ITS
SOLUTION...PARTICULARLY GIVEN THE ENSEMBLE SUPPORT.

...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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