Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1206 PM EST Mon Mar 05 2018

Valid Mar 05/1200 UTC thru Mar 09/0000 UTC

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

12Z model evaluation...along with model preferences and confidence
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...Central Plains/Midwest storm system today...
...Passing off to developing East Coast nor'easter by Wednesday...
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Preference: General model blend...through 36 hours
            12Z GFS...after 36 hours
Confidence: Above average...become average after 36 hours

The models take the negatively tilting trough and evolving deep
layer closed low ejecting out across the central/northern Plains
off to the east through the Midwest on Tuesday. As this occurs,
there will be an increasing degree of binary interaction with a
closed low over Ontario with this separate closed low feature
beginning to rotate around the north side of the Midwest storm.
The models shows very good agreement through Tuesday in taking a
sizable portion of energy/height falls with the Midwest system off
to the east and toward the Ohio Valley. By Tuesday night, the
upper trough should take on a negative tilt across the Ohio Valley
and then the central Appalachians as a 130+kt 250 mb jet max
rounds the base of the trough through the Tennessee Valley. This
will ultimately allow the system to deepen further and all of the
models show a closed low crossing the Mid-Atlantic region on
Wednesday before then lifting up across or very near southern New
England. The result will be surface low evolution that initially
focuses over the upper Midwest but then evolves east-southeast
across the Ohio Valley through Tuesday. On Tuesday night, the Ohio
Valley low will weaken and secondary low pressure developing over
the Southeast coastal plain will lift up off the Virginia Capes by
early Wednesday and become the dominant low center. The low will
deepen further through Wednesday and Wednesday night as the low
lifts just offshore New Jersey, Long Island and adjacent areas of
southern New England. On Thursday, the system will lift up across
the Gulf of Maine.

Model spread with the entire system is mostly centered on the East
Coast/nor'easter evolution. The 12Z NAM gradually focuses its low
center a bit west of the model consensus, with the 00Z CMC AND 00Z
ECMWF farthest east. The 12Z GFS and 00Z UKMET split the
difference, with the GFS a bit west of the UKMET. There has been
some westward trending of the NAM and GFS guidance over the last
24 hours, and also the GEFS members from 06Z. This is likely
related to the details of a persistent and relatively strong
blocking ridge over eastern Canada. It is feasible that some
additional westward shifting of the guidance may occur, and
especially as it relates to the low track relative to New England
since the guidance maintains this blocking pattern. Also, the
guidance takes the closed low feature dropping south over Ontario
down to the southeast toward the Ohio Valley by Thursday which may
help to back the large scale flow enough for the New England
closed low/nor'easter to track farther left. Overall, WPC is
favoring a general model blend through 36 hours, and then a
solution very close to the 12Z GFS thereafter.
 

...West Coast/Northwest U.S....
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Preference: Blend of the 12Z GFS and 00Z ECMWF
Confidence: Slightly above average

The large scale flow pattern will consist a deep closed low near
38.5N 142.0W initially that advances off to the east and
approaches the West Coast by late Wednesday and then moves inland
across the Northwest U.S. through Thursday. Surface low will
arrive across coastal Oregon on Thursday along with a well-defined
cold front sweeping in across the coastal ranges. The 12Z NAM and
00Z CMC are a bit stronger with the arrival of the system as
compared to the 12Z GFS and 00Z ECMWF. The latter camp is very
well clustered and has very good ensemble support and so will
prefer a blend of the GFS and ECMWF at this time.

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

Orrison