Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
241 AM EDT Sun Sep 22 2019

Valid Sep 22/0000 UTC thru Sep 25/1200 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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...Synoptic Overview...
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The synoptic pattern will feature a deep layer ridge over the
Southeast through Sunday, as a pair of robust northern stream
troughs traverse the western and central U.S. The first trough
will advance east across the upper Midwest through Sunday along
with an attendant cold front and a wave of low pressure riding up
along it. This energy will break down the ridge over the Southeast
and allow a cold front to arrive across the OH Valley and lower
Great Lakes region by Monday. The height falls are expected to
sharpen over the Northeast by Tuesday as an upper low deepens and
fosters cyclogenesis over northern New England. This will advance
the upstream cold front across the East Coast. Meanwhile, a second
upstream trough will cross the West Coast and move into the Great
Basin by Monday before then cutting off from the westerlies and
dropping down into the Southwest on Tuesday. This upper trough
will tap some of the remaining moisture and energy associated with
weakening Tropical Storm Lorena which will be crossing northwest
Mexico. By Tuesday and Wednesday, a new northern stream trough
will dig across the northern Plains and upper Midwest along with a
cold front.


...Deep trough crossing the Plains/Midwest through Sunday...
...Energy closing off over the Northeast early next week...
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Preference: General model blend...through 60 hours
            Non-GFS blend...after 60 hours
Confidence: Above average

Model differences with the first trough are rather small through
most of the weekend as the energy crosses the Intermountain West
and advances across the Plains and Midwest, but by later Monday
and Tuesday as the energy crosses the Great Lakes and moves into
the Northeast, the 00Z GFS becomes a bit more progressive than the
remaining well clustered guidance. Will recommend a general model
blend through about 60 hours, and then a non-GFS blend thereafter.


...Upper trough digging into the West by Monday...
...Closed low evolution over the Southwest by Tuesday...
...Moisture/energy associated with T.S. Lorena...
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Preference: General model blend
Confidence: Average

Regarding the second trough moving into the West, the model
guidance is well clustered and in good agreement with respect to
timing and depth through most of Monday, and has come into much
better agreement with the details of the closed low evolution as
the energy digs south into the Southwest on Tuesday. The 00Z CMC
and 00Z UKMET have both trended strongly toward the 00Z
NAM/GFS/ECMWF cluster, and all of the models show a closed low
feature near the northern Gulf of CA or just a tad east of here
over northwest mainland Mexico by early Wednesday. The CMC by the
end of the period is just a tad east of the model consensus. It
should be noted though that despite the much better deterministic
model clustering with the 00Z cycle, the 00Z GEFS mean is still
farther east with the closed low solution, which is suggestive
that there is still a fair degree of uncertainty and a potential
for the deterministic guidance to shift back farther east for this
period. In any case, all of the models do indicate some
interaction with the remnant moisture and energy associated with
weakening Tropical Storm Lorena which is expected to lift across
northwest Mexico Sunday before then dissipating Sunday night.
Given the much better deterministic clustering with the closed low
evolution, the preference will now be for a general model blend.


...Upper trough over the northern Plains by Tuesday...
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Preference: General model blend...through 60 hours
            Non-GFS blend...after 60 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 High Plains by Tuesday and upper Midwest by Wednesday.
The 00Z GFS is just a tad sharper and more progressive than the
remaining guidance toward the end of the period. The 00Z GEFS mean
suggests a modestly slower solution that is closer to the
remaining well-clustered multi-model consensus. So, will prefer a
general model blend through about 60 hours, and a non-GFS blend
thereafter.


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

Orrison