Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
250 PM EDT Mon Jul 13 2020
Valid Jul 13/1200 UTC thru Jul 17/0000 UTC
...See NOUS42 KWNO (ADMSDM) for the status of the upper air
ingest...
12Z Model Evaluation with Final Preferences/Confidence
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...Mid-level shortwave troughing over the northeastern quarter of
the U.S. Monday to Wednesday...
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Preference: General model blend
Confidence: Average
The 12Z NCEP guidance maintained good run to run continuity with
this feature, in terms of the depth and the speed of the system
while the 12Z ECMWF was a bit quicker (apparently in response to
the southern U.S. ridge being some 20 meters weaker than in
previous runs of the ECMWF). Given the small differences, a
general model blend will work fine although a bit less weight
should be given to the slower ECMWF/UKMET.
...Longwave trough axis moving through the north-central U.S.
through Wednesday with accompanying surface cold front...
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Preference: 13/12Z GFS/NAM/ECMWF/CMC blend
Confidence: Average
The 12Z NCEP and non-NCEP guidance maintained good run to run
consistency here, too, with a broad 500 mb trough and associated
surface cold front moving across the central to northern Plains
later tonight into Tuesday. Some minor timing and amplitude
differences continue to be seen, with the 13/12Z GFS a bit faster
and stronger with mid-level height falls across the Upper Midwest
into the western Great Lakes region...but with the ECMWF/CMC also
nudging a bit faster in the 12Z model cycle...the overall
differences have diminished a bit. At the surface, the NCEP
guidance continued to be more progressive than the ECMWF and
UKMET. Based on the fact that the models tended to show a speed
max at jet level aiding upper level divergence over that region,
am inclined to favor the faster/stronger solutions. Perhaps the
GFS was a bit too aggressive here, especially looking at the
thermal fields in low levels, but not enough to discount its
solution.
...Cut off low west of California by Thursday morning...
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Preference: General model blend
Confidence: Average
Good model agreement exists with a 700-500 mb low closing off by
mid-week from a weak and nearly stationary trough axis in place
over the western U.S. today. The latest guidance shows very little
in the way of differences with the timing, placement and strength
of this feature. Therefore, a general model blend will be used for
the preference.
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