Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Mon Oct 07 2019

Valid Oct 07/1200 UTC thru Oct 11/0000 UTC

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

12Z Model Evaluation with Preferences and Forecast Confidence
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...Upper trough crossing the Great Lakes/Northeast...
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Preference: General model blend
Confidence: Above average

The models show very good agreement with the details of the upper
trough and associated shortwave energy crossing the Great Lakes
and northern New England today through Tuesday. A general model
blend will be preferred.


...Energy amplifying over Central Appalachians/Mid-Atlantic...
...Deepening surface low pressure off the East Coast...
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Preference: Non-GFS blend
Confidence: Slightly below average

The guidance again shows shortwave energy advancing across the
mid-MS and OH Valleys that will break away from the westerlies and
amplify toward the central Appalachians through Tuesday, with at
least a weak mid-level closed low evolving near the northern
Mid-Atlantic region by Wednesday. On Thursday, the models support
the closed low feature being generally southeast of Long Island.

Of the 12Z cycle of guidance, the NAM, UKMET, CMC and ECMWF are
all clustered toward a stronger solution compared to the GFS. In
fact, the UKMET and ECMWF both trended strongly toward each other
regarding intensity and placement of their mid-level low centers.
The CMC is just a tad east of this consensus, but the modestly
weaker GFS is farther south. This energy is expected to interact
with an area of disturbed weather northeast of the Bahamas that
will be lifting northwest to offshore of the Carolinas on Tuesday.

The guidance is in very good agreement in depicting offshore
cyclogenesis as the upstream height falls approach the East Coast,
but there remains some important spread by the end of the period
with where the low center will be focused. The GFS is weakest and
farthest south, with the UKMET and ECMWF both clustered farthest
northwest and closest to southeast New England which results in
some potentially significant rainfall concerns by Thursday. The
NAM and CMC are a tad south and east respectively compares to the
UKMET/ECMWF cluster. Unfortunately, the 12Z GEFS mean resides with
the GFS which elevates the uncertainty in the forecast, but the
00Z ECENS mean does have a membership envelope that supports the
non-GFS cluster of solutions. Thus, based on the latest trends and
clustering, a non-GFS blend will be preferred, but again with
somewhat limited confidence.


...Weak surface low pressure impacting the FL Peninsula...
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Preference: General model blend
Confidence: Above average

Meanwhile, a separate area of disturbed weather associated with a
tropical wave/surface and weak area of low pressure will be
advancing west across south Florida today and tonight which will
advance into the eastern Gulf of Mexico on Tuesday before
weakening and losing its identity. A general model blend can be
preferred with this system.


...Deep upper trough/closed low amplifying over the West...
...High Plains cyclogenesis...
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Preference: Blend of the 12Z GFS/UKMET/ECMWF
Confidence: Slightly above average

The models are in very good agreement on amplifying a northern
stream trough down toward the Pacific Northwest, northern Rockies
and northern High Plains later today and which will send a very
strong cold front southeast from Canada along with much colder
air. As the cold front advances southeast, one wave of low
pressure will develop along it over southeast MT by late Tuesday
which will cross the Dakotas through early Wednesday before then
dampening out. The models show excellent agreement with this
evolution. Then as the cold front advances down the Front Range of
the Rockies by late Wednesday, a new area of strong cyclogenesis
is expected to take place over eastern CO which will then advance
east and elongate along the front on Thursday as it crosses the
central Plains. The NAM gradually becomes a bit stronger than the
global models with its depth of the trough and closed low over the
Intermountain West by late Wednesday and Thursday. The CMC by the
end of the period appears to be placing the core of its height
falls a bit too far north over the northern High Plains as the
guidance suite supports a consolidation of mid-level energy
farther south closer to the central Rockies. The CMC as a result
ends up being a bit more out of phase at the surface with its cold
front compared to the other models. The better model clustering
and ensemble support at this point favors a blend of the GFS,
UKMET and ECMWF, and so a blend of these solutions 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