Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
159 PM EST Sat Feb 09 2019

Valid Feb 09/1200 UTC thru Feb 13/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Western U.S...
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Preference: General model blend...through 60 hours
            Blend of the 12Z GFS/CMC/ECMWF...after 60 hours
Confidence: Above average

An active weather pattern will continue to evolve as a series of
northern stream troughs/closed lows drop south just off the
Pacific Northwest. Already there is one shortwave trough that is
moving inland across California which the guidance has ejecting
progressively downstream across the Intermountain West tonight
before it ejects out into the Plains on Sunday. There is little
model mass field spread with this system as it crosses the West.
Meanwhile, a strong deep layer closed low currently seen in IR/WV
satellite imagery just offshore of WA/OR is settling gradually
down to the south. This energy will pivot inland across the Great
Basin and Rockies Sunday and Monday as a new deep layer closed low
drops down from southern B.C and across WA state. All of this
energy will shift off to the east out into the High Plains by late
Monday. There is reasonably good model agreement with the details
of these height falls through Monday. By Monday night and Tuesday,
there will be yet another deep layer closed low and associated
trough axis dropping south near and offshore of the Pacific
Northwest. The 12Z NAM becomes a deep outlier with this energy,
with the 12Z UKMET appearing to be too slow and too far offshore
with its closed low by the end of the period. The 12Z GFS and 12Z
CMC are well-clustered with this system, and also now have good
support from the 12Z ECMWF. This cluster is well-supported by the
12Z GEFS mean and 00Z ECENS mean as well. Thus, based on the
latest trends, will prefer a general model blend through 60 hours,
and a blend of the GFS, CMC and ECMWF thereafter.


...Central/Eastern U.S...
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Preference: 12Z ECMWF/12Z GEFS mean/00Z ECENS mean blend
Confidence: Below Average

The lead shortwave trough that ejects across the Plains and Upper
Midwest on Sunday will gradually dampen out as it approaches the
Great Lakes region. The 12Z NAM appears to be a relatively deeper
outlier with this energy compared to all of the global models, and
a non-NAM blend can be preferred with this feature.

The next system will be the ejecting large scale trough out of the
West by Monday which will drive cyclogenesis over the Plains in
the lee of the central Rockies. The 12Z GFS remains a bit north of
the non-NCEP models with this low evolution through late Monday
and including the 12Z NAM. However, here is still some 12Z GEFS
member support for this farther north track. The 00Z ECENS member
suite overall favors a solution a little south of the
deterministic GFS and just a tad north of the 12Z ECMWF through
late Monday.

By Tuesday, the models diverge rather wildly with the evolution of
surface low pressure over the Midwest and Great Lakes as the
longwave trough takes on a negative tilt. The 12Z NAM ultimately
ends up being stronger and farther north with the entire height
fall and surface low evolution. The 12Z CMC ends up being much
weaker and more suppressed and is on the south side of the model
suite. The 12Z UKMET ends up being a rather weak as well and also
more progressive. The 12Z GFS and 12Z ECMWF still have some
latitudinal differences, but the ECMWF did trend a bit farther
north and also more progressive which at least affords somewhat
better low track agreement. Overall, the GFS is still a bit north
of the ECMWF, but one concern with the GFS is that it is likely
too strong owing to its deeper 500/700 mb low/trough axis compared
to the other models. The 12Z GEFS mean actually favors a
compromise between the GFS and ECMWF with the low track and
intensity and is supported by the 00Z ECENS mean as well. So,
based on the latest model trends, a blend of the ECMWF, GEFS mean
and ECENS mean will be preferred. However, given the overall
deterministic model spread, confidence remains low as to the
ultimate low track and intensity on Tuesday.


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

Orrison