Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1110 AM EST Fri Nov 23 2018

Valid Nov 23/1200 UTC thru Nov 27/0000 UTC

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

12Z Model Evaluation...with Initial Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Mid Atlantic to northeast...
Preference: Thu 12z ECMWF
Confidence: Average

On Saturday to Sunday, low pressure develops along the mid
Atlantic coast and moves north, with timing and phasing
differences remaining. The 00z UKMET was on the northwest fringe
of low tracks, and 00z ECMWF and Canadian models a few hours
faster.  The 00z ECMWF ensemble mean was south of the operational
run with its forecast low positions and closer to  the 12z Thu
operational ECMWF. Given good agreemenent between the 12z Thu
ECMWF and 00z ECMWF Ensemble Mnea, this combination is preferred
for the low track.

The 12z NAM trended further offshore with its low track and on 12z
Sun is a southern outlier. Consequently, confidence is low with
the 06z NAM likely a better option than the 12z run. Confidence is
also low with the GFS track turning further offshore.

...Central Rockies to Central Plains and Great Lakes...
Preference: A blend of the 00z UKMET and 12z NAm
Confidence: Average

On Saturday, low pressure developing in Wy moves and redevelops as
a lee low in CO that then moves to near the OK/MO/KS border by 12z
Sun, then turns northeast towards the Great Lakes. Timing and
phasing differences develop with the 12z GFS and 00z Canadian on
the fast side of the guidance spread and 00z ECMWF on the slow
side.  These situations usually get resolved with an intermediate
solution somewhere in between the GFS and ECMWF, represented by
the 12z NAM/00z UKMET, and 00z ECMWF ensemble mean.

The 00z ECMWF becomes a minority solution with the phasing of the
upper low west of Hudson Bay on Monday, which forces a distinct
500 mb shortwave to develop with a downstream ridge in the midwest
not shown in most ECMWF ensemble members.

...Pacific Northwest...
Preference: Blend of the ECMWF and GFS
Confidence: Slightly Above Average

Rain develops in the Pacific northwest Mon as a low moves north of
Vancouver Island.
The models are in good agreement on latitude of the system,
lending itself to a consensus based approach (no strong
preference) of the NAM/GFS/SREF Mean/ECMWF/UKMET.

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

Petersen