Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
127 PM EDT Sat Oct 05 2019

Valid Oct 05/1200 UTC thru Oct 09/0000 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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...Overall Pattern Across the CONUS...
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Preference: General model blend...Central/Western U.S.
            12Z GFS/06Z GEFS/00Z ECENS blend...Eastern U.S.
Confidence: Average

The large scale flow pattern across the CONUS over the next few
days will feature a strong upper trough advancing east across the
upper Midwest and Great Lakes region through Sunday with a
trailing cold front that will cross the mid-MS Valley and then
reach toward the East Coast by Monday as the bulk of the energy
with the upper trough lifts northeast up across Canada. The
guidance is in very good agreement with the details of this
evolution, but there is some spread in the guidance with respect
to a shortwave trough digging southeast across the Midwest and
toward the OH Valley in the wake of this energy.

The guidance suggests this energy will break away from the
westerlies and amplify toward the central Appalachians by later
Monday and Tuesday. The 00Z ECMWF and to some extent the 00Z CMC
are on the stronger side of the model suite compared to the 12Z
NAM/GFS and 00Z UKMET. The evolution of this weakness developing
over the central Appalachians will be critical as there are
indications this energy will interact with the northwest advance
of a surface trough/tropical wave lifting northwest across the
Bahamas and up off the East Coast. In fact, all of the models on
the one hand suggest a weak low center crossing the northwest
Bahamas and moving into south Florida by late Monday, with then an
area of cyclogenesis occurring well east of the Carolinas by
Tuesday. There is a fair amount of latitudinal spread in the
guidance with where this secondary cyclogenesis will initially
occur as the ECMWF is the farthest north and the UKMET much
farther south.  By the end of the period, the GFS and CMC tend to
support the ECMWF, with the NAM supporting the UKMET. Overall, the
GEFS mean and ECENS means favor the GFS/ECMWF camp, but the
ensemble means suggest for now that the deterministic ECMWF is a
bit too aggressive over the central Appalachians with the closed
mid-level low center.

Elsewhere, there will be a new northern stream trough amplifying
down toward the Pacific Northwest, northern Rockies and northern
High Plains by later Monday and Tuesday which will send a strong
cold front southeast from Canada along with much colder air. There
are some very modest timing differences with the front, but in
general the guidance is in good agreement.

Based on the latest model clustering and spread, a general model
blend will be preferred across the central and western U.S., with
a blend of the 12Z GFS, 06Z GEFS mean and 00Z ECENS mean across
the eastern U.S. and offshore the East Coast.


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

Orrison