Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1122 PM EST Sun Jan 27 2019

Valid Jan 28/0000 UTC thru Jan 31/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern across the CONUS...
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Preference: General model blend
    West Coast: 00z GFS
Confidence: Above Average
    West Coast: Slightly above average

The synoptic to global scale model agreement continues to be
excellent with the large vortex over the Great Lakes and the
Pacific ridge breaking down under the influence of a
strong/compact wave that will drive into the Central CA coast
toward the end of the forecast period, so confidence is fairly
high to start with.  However, as one delves into the sub-synoptic
to mesoscale, some key differences unfold to remain a bit guarded.
  The 00z NAM shows some of these details even as early as the
overnight Monday into Tuesday, driving the cold air further west
on stronger CAA, leading to a slight amplification.  This angle
supports further north deep cA airmass to drop more south than
southeast into the Midwest delaying the inner core of the close
upper low; which in turn delays its drive through New England with
greater height falls/negative tilt into E Canada, offsetting the
global cyclone a bit NE of the other guidance.  This is very picky
in the otherwise very good agreement but does lead to some caution
overall.  The 00z GFS typical of its bias, it a bit fast pressing
the lead shortwave height-falls through the TN valley by Tues and
likewise should not be used verbatim.  On the slow side is the 12z
CMC, relative to the overall suite, leaving languishing troughing
across the Great Lakes by early Thurs.  Again, these are very
picky subtle issues and a general model blend can be employed to
alleviate these concerns at high confidence.

Further west, the persistent ridge will begin to break down with
the approach of the strong/compact/pattern changing closed low
that reaches the 40N130W benchmark around early Wed.  The ECMWF is
in a very atypical location leading the pack though continues a
trend toward slowing as well as tempering the extreme depth of the
wave, but still may be too far east to favor.  Similarly, the
UKMET is in the atypical position of being last through the ridge
and stands out significantly in the WPC ensemble spaghetti
analysis/run to run cycle trend.  The 00z NAM showed the greatest
transition (though last to the party) with the deeper compact
system, and is generally further south moving through the dying
ridge.  The 12z CMC and 00z GFS show greatest agreement and are
generally in line with the ECMWF with exception to entering
central California a bit further north.  Overall, favoring the 00z
GFS, given its retention of strength and track very central to all
of the main ensemble means (ECENS, GEFS, NAEFS/CMCE).  While a
blend with the CMC or even the NAM may be ok...think favoring the
00z GFS outright may be best at this point at slightly above
average confidence.

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

Gallina