Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1253 AM EDT Mon Sep 23 2019

Valid Sep 23/0000 UTC thru Sep 26/1200 UTC

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

00Z Model Evaluation with Preferences and Forecast Confidence
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...Deep trough crossing the Great Lakes on Monday...
...Energy closing off over the Northeast by Tuesday...
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Preference: General model blend...through 48 hours
            Non-CMC blend...after 48 hours
Confidence: Above average

Model differences with the height falls of this system are very
small going through Monday and Tuesday as the energy crosses the
Great Lakes and moves through the Northeast. By Wednesday, the
closed low feature will advance across the southeast Canadian
maritimes, at which time the 12Z CMC becomes a slower and
southerly tracking outlier solution. Will prefer a general model
blend through 48 hours, followed by a non-CMC blend thereafter.


...Upper trough digging into the West by Monday...
...Closed low evolution over the Southwest...
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Preference: Non-UKMET blend
Confidence: Average

Regarding the next trough moving into the West, the model guidance
is well clustered and in good agreement with respect to the timing
and depth of it through Monday. By Monday night, all of the models
again dig the height falls into the Southwest, with a well-defined
closed low evolution by Tuesday that becomes cut off from the
westerlies. The 12Z UKMET positions its closed low a bit west of
the otherwise well clustered multi-model suite. The closed low is
expected to settle as far south as the northern Gulf of CA or just
a tad east of here over northwest mainland Mexico by Wednesday
before the system then begins to slowly push off to the northeast.
While the UKMET is on the western end of the deterministic
guidance, it is again noted the that the GEFS mean (18Z cycle) is
farther east and east of all of the deterministic solutions and
also the ECENS mean (12Z cycle). For now, the preference will be
for a non-UKMET deterministic blend.


...Upper trough over the northern Plains/Midwest by Tuesday...
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Preference: General model blend...through 36 hours
            Non-GFS blend...after 36 hours
Confidence: Above average

The models have good agreement overall with the details of a
northern stream trough and associated cold front crossing the
northern Plains and Midwest Tuesday and Wednesday. By Thursday,
the trough is expected to be advancing through the Great Lakes
region. The 00Z GFS is a tad sharper and more progressive with the
height falls compared to the remaining guidance from about 36
hours onward. So, will prefer a general model blend through 36
hours, and a non-GFS blend thereafter.


...Upper trough approaching the Pacific Northwest by Thursday...
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Preference: Multi-model consensus of 12z ECMWF/12z UKMET/06z GFS
Confidence: Slightly Above average

The next in a series of shortwaves rounding the top of the very
strong deep layer ridge offshore of the West Coast will dig
southeast from the Gulf of AK on Wednesday and will approach the
Pacific Northwest by Thursday. The guidance is fairly well
clustered with the timing and depth of this system, with exception
of the 00Z GFS which is notably weaker and out of phase compared
to the remaining guidance as the energy approaches the Pacific
Northwest. A non-GFS blend will be preferred.


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

Orrison