Prognostic Meteorological Discussion
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000
FXUS10 KWNH 111848
PMDHMD

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
247 PM EDT Tue Aug 11 2020

Valid Aug 11/1200 UTC thru Aug 15/0000 UTC

...See NOUS42 KWNO (ADMSDM) for the status of the upper air
ingest...

12Z NAM/GFS Evaluation Including Preferences and Forecast
Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Longwave troughing over the Northwest to the Northern Plains
Tuesday through Thursday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of 11/12Z ECMWF and 11/12Z GEFS Mean
Confidence: Slightly above average

Model consensus is for a longwave trough to amplify across the
Pacific northwest into northern CA in response to upstream ridging
along 155W. Low amplitude shortwaves eject and move east northeast
across the northern Rockies and northern Plains which gradually
helps to shift the trough axis east across the northern Rockies
and high Plains by Thursday. Minor timing differences develop,
with the 11/12Z operational GFS remaining on the faster side of
the envelope of solutions.  Given the GFS bias of being too quick,
prefer a combination of the most recent ECMWF and GEFS Mean which
offer a somewhat slower solution but maintains overall continuity
with previous runs.


Mid to Upper MS Valley
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of 11/12Z GFS and 11/12Z ECMWF
Confidence: Average

Of the 11/12Z NCEP suite, the GFS appeared to have fewer problems
with generating convectively induced vorticity maxima than the
NAM.  Will continue to favor the GFS and ECMWF given


Southeast to Mid Atlantic
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of 11/12Z GFS and 11/12Z ECMWF
Confidence: Slightly Above Average

The models show a high amplitude ridge over the western Atlantic
that keeps a mid level trough over the eastern Carolinas and
Georgia in place or drifting slowly.  Of the operational global
models, the most recent versions of the ECMWF and GFS continue to
be in good agreement...and non-NCEP models made only minor changes
compared with their previous runs.  Therefore we see little reason
to change the on-going preference at this time.


Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

This product will terminate August 15, 2020:
www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination.
pdf

Bann


$$




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