Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
257 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.
            Blend of the 12Z GFS and 12Z ECMWF...Eastern U.S.
Confidence: Slightly above 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 the initial trough passage.

The guidance suggests the secondary shortwave energy will break
away from the westerlies and amplify toward the central
Appalachians by later Monday and Tuesday. The 12Z CMC is on the
stronger side of the model guidance, with the 12Z UKMET the
weakest. The 12Z NAM/GFS and 12Z ECMWF are rather well clustered
in between, with the GFS overall a tad stronger than the NAM and
ECMWF. By the end of the period, there is support for at least a
weak mid-level closed low and associated trough axis near the
central Appalachians. 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 as the upstream height falls approach the East Coast.
There is a fair amount of latitudinal spread in the guidance with
where this secondary cyclogenesis will initially occur as the
ECMWF/CMC solutions are farther north and the UKMET much farther
south. By the end of the period, the CMC ends up being the
farthest north followed by the GFS and ECMWF. The NAM supports the
UKMET with a farther south solution. Overall, the GEFS mean and
ECENS means favor the northerly camp of solution.

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 modest timing differences with the front, most notably
led by the 12Z UKMET which overall appears to be too slow with the
front by the end of the period. Otherwise, the model agreement is
rather good.

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 and 12Z ECMWF 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