Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
110 PM EDT Sun Aug 09 2020
Valid Aug 09/1200 UTC thru Aug 13/0000 UTC
...See NOUS42 KWNO (ADMSDM) for the status of the upper air
ingest...
12Z NAM/GFS Evaluation Including Preliminary Preferences and
Forecast Confidence
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...Longwave troughing over the Northwest Tuesday-Wednesday...
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Preference: non 12Z GFS blend
Confidence: Average
As a broad mid-upper level trough axis translates eastward from
the northeastern Pacific early this week, reaching southwestern
Canada and the northwestern U.S. Tuesday into Wednesday. Of the
latest guidance, only the 12Z GFS stands out with a slower
progression of a shortwave into Washington and Oregon late
Wednesday. For now, prefer to go toward the stronger consensus,
outside of the 12Z GFS.
...Weak troughing/surface low along the southeastern U.S. coast on
Wednedsay.
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Preference: 12Z GFS, 00Z ECMWF, 00Z UKMET blend
Confidence: Below average
Model forecasts take an existing MCV over the Lower Ohio Valley
from Sunday morning, southeastward toward the Carolinas by
Wednesday morning. The models differ in strength regarding this
feature with most developing a surface low into the Southeast and
near the coastline. The ensembles depict this feature rather well,
and while single model is an outlier, the 12Z NAM is strongest and
00Z CMC lies on the eastern edge of the latest spread. The 12Z GFS
is weakest but a blend if the GFS with the 00Z ECMWF and 00Z UKMET
appears to be the best compromise for this system.
...Remainder of Overall weather pattern across the continental U.S.
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Preference: General model blend led by the 12Z GFS and 00Z ECMWF
Confidence: Average
The remainder of the U.S. will feature quasi-zonal flow across the
northern half of the nation with a bi-modal ridge centered over
the Lower Mississippi Valley and southern Arizona/New Mexico. A
large closed low will track east across Canada with some weakening
through Wednesday. A cold front will follow at the surface with
potential for convective flare ups near the frontal boundary.
While differences exist with the models regarding these flare ups
and their impacts on the mid-levels, no single model can be ruled
out with any confidence. At this time, a general model blend is
preferred but with the most weight toward the 12Z GFS and 00Z
ECMWF as they are closer to the middle of the model spread with
features across the remainder of the U.S., not already discussed
in the above sections.
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
Otto