Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1130 PM EST Sat Nov 10 2018

Valid Nov 11/0000 UTC thru Nov 14/1200 UTC

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

12Z Model Evaluation...with Final Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: General Model Blend...Day 1
            00Z GFS/18Z GEFS and 12Z ECMWF/ECENS blend...Day 2/3
Confidence: Average

The upper level flow across the CONUS initially features a deep
layer ridge just off the West Coast with a downstream longwave
trough across the central U.S. Meanwhile, a deep closed low is
seen exiting northeast and away from the Northeast and up across
Quebec as flat zonal flow is noted farther south across the
southern tier of the nation. Over the next 36 to 48 hours, the
deep layer ridge off the West Coast will shift east into the
Western U.S. as a deep closed low advances into the Gulf of AK.
Multiple shortwave impulses will be dropping down the east side of
the ridge as it moves east and this will lead to a much more
amplified pattern downstream with an amplifying trough across the
central and southern High Plains Sunday and Monday which then
gradually advances east across the lower MS Valley on Tuesday.
Meanwhile, the guidance shows a bit of stream separation with
time, and by Monday and Tuesday there will be a more pronounced
northern stream trough digging across the upper Midwest and Great
Lakes region. Surface low pressure will develop over the western
Gulf of Mexico by early Monday in response to the energy digging
across the southern Plains and lower MS Valley and will lift
northeast and up across the interior of the Southeast through
Monday night. Secondary low pressure that will be more tied into
the amplifying northern stream trough over the Midwest and Great
Lakes is expected to form along a coastal front by early Tuesday
near the Mid-Atlantic coast and then lift north across southern
and eastern New England Tuesday night and across Atlantic Canada
on Wednesday. Elsewhere, by the end of the period, the ridge over
the western U.S. will have broken down and there should be a
shortwave coming into the Pacific Northwest by that time as
supported strongly by all of the models.

The model mass field spread is rather minimal through early
Monday, although the 00Z NAM begins to amplify the upper trough
digging across the Four Corners region and southern High Plains a
bit more aggressively than the global models by that point.
Thereafter, the NAM goes on to become a deeper and slower outlier
with the evolution of the southern stream energy/troughing as all
of the global models are more progressive and support an elongated
positively tilted trough cutting across the lower MS and TN
Valleys through Tuesday and Wednesday. The NAM results in more
backing of the mid/upper level flow down stream across much of the
lower MS and TN Valley region which also results in heavier QPF
becoming focused a bit north and west of the global model
consensus. The NAM along the East Coast also has a surface low
that develops faster and lifts quicker up toward southern New
England by Tuesday. The models though do actually diverge a bit
with the low track Tuesday night and early Wednesday as it impacts
New England with the 00Z NAM/GFS solutions a bit east of the
non-NCEP solutions involving the 12Z UKMET/CMC/ECMWF.

Based on the latest model trends, and clustering of deterministic
and ensemble solutions, a general model blend will be preferred
out through Day 1, and then a 00Z GFS/12Z ECMWF blend thereafter
and also including the 18Z GEFS mean and 12Z ECENS mean. This will
foster a compromise with the trough/low evolution across the East
through the Day 2/3 period and will also nicely approximate the
model consensus across the West as the deep layer ridge gradually
breaks down and shortwave energy arrives across the Pacific
Northwest by the end of the period.


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

Orrison