Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
105 PM EDT Sun Oct 06 2019

Valid Oct 06/1200 UTC thru Oct 10/0000 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 through Monday...
...Attendant cold front moving into the East...
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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 that will be crossing the
upper Midwest and Great Lakes region through Monday. An attendant
cold front will cross the OH Valley and move toward the East Coast
by Monday night. A general model blend will be preferred.


...Shortwave energy amplifying over the Mid-Atlantic...
...Deepening surface low pressure off the East Coast...
...Weak surface low pressure impacting the FL Peninsula...
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Preference: Blend of the 12Z GFS/00Z UKMET/00Z ECMWF
Confidence: Below average...except above average over FL

The guidance again suggests secondary shortwave energy advancing
across the mid-MS and OH Valleys that will break away from the
westerlies and amplify toward the central Appalachians by later
Monday and Tuesday, and with at least a weak mid-level closed low
evolving near the northern Mid-Atlantic region by Wednesday. The
00Z CMC is on the stronger side of the model guidance and is also
a bit farther north of the model consensus with the height fall
evolution. 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 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 occur, but all of the models have
collectively trended toward a low center tucking in closer to the
Eastern Seaboard by Wednesday. The 00Z CMC ultimately ends of
deeper and farther north with the low center, with the 00Z ECMWF
farthest south. The 12Z GFS is now a bit west of the 06Z GEFS mean
and northwest of the 00Z ECENS mean. The 12Z NAM and 00Z UKMET
cluster just a little north of the ECMWF and southeast of the GFS.
Based on the latest trends, including the westward shift in the
GFS, a non-CMC blend led by a consensus of the GFS, UKMET and
ECMWF will be preferred for the time being. Confidence is limited
with the offshore low center evolution, but is above average with
respect to the separate low center impacting the FL Peninsula.


...Deep upper trough/closed low amplifying over the West...
...High Plains cyclogenesis...
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Preference: General model blend
Confidence: 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 by later Monday and Tuesday 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. 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. Given the level of model agreement with the
details of the frontal timing across the Great Basin and the High
Plains, the pair of low centers, and the deep trough/closed low
evolution expected over the Intermountain West, a general model
blend will be preferred with above average confidence.


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

Orrison