Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
156 PM EST Fri Mar 02 2018

Valid Mar 02/1200 UTC thru Mar 06/0000 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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...Powerful nor'easter impacting the Mid-Atlantic/Northeast...
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Preference: General model blend
Confidence: Above average

The models are in very good agreement in taking the strong
nor'easter currently impacting the Mid-Atlantic and Northeast off
to the east and out to see over the next 24 to 36 hours. A general
model blend will be preferred at this time given good model mass
field clustering.


...Deep closed low impacting the Western U.S. through Saturday...
...Negatively tilted trough approaching the Plains on Sunday...
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Preference: General model blend...through 60 hours
            12Z GFS/12Z UKMET/12Z ECMWF blend...after 60 hours
Confidence: Slightly above average 
 
The models all take a strong closed low offshore the Pacific
Northwest today gradually south which broadens out over the next
day and then moves inland across the Intermountain region. This
will allow a broad trough to envelope all of the West through
Sunday. The guidance though indicates that energy lifting out of
the base of the trough by late Sunday will allow the trough to
take on a negative tilt out across the central/northern Plains
through Monday before then closing off in the mid levels. Surface
low pressure over the Great Basin through Sunday is expected to
reorganize over the Plains on Monday and begin lifting toward the
upper Midwest. The guidance is generally in good agreement with
their timing and depth of the trough evolution through early
Monday, but by the end of the period there are some latitudinal
differences with the closed low evolution and the intensity of
surface low pressure. The 12Z ECMWF is still on the north side of
the guidance by the end of the period, with the 12Z UKMET a little
farther south. The 12Z NAM and 12Z GFS are well clustered with
their timing/placement of the height falls, but the GFS is
stronger at the surface. The 12Z CMC is a tad on the faster side
of the model spread. Given the gradual consolidation noted among
the GFS, ECMWF and UKMET solutions, a blend of these models will
be preferred after 60 hours, with a general model blend prior to
this.


...Trough digging southeast across the Northeast on Monday...
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Preference: Blend of the 12Z GFS and 12Z ECMWF
Confidence: Average

The models take a portion of the trough/closed low just southwest
of Hudson Bay and slowly shift it southeast across Quebec on
Sunday and then in more of sheared fashion down across the
Northeast on Monday as the system encounters a blocking high that
is settling southwest from southern Greenland. Not every model
shears all of the energy down across the Northeast though as the
12Z NAM, 12Z GFS, 12Z ECMWF and the 12Z CMC keep a sizable degree
of energy up across southeast Canada to the west of the blocking
ridge. The 12Z UKMET was more emphatic on bringing more energy
farther southeast across the Northeast. Regarding the best model
clustering, the GFS and ECMWF are the closest and have support
from the latest GEFS mean. Will favor a blend of the GFS and ECMWF
at this time as a result.

 
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