Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
309 PM 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 Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Mid Atlantic to northeast...
Preference: Fri 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/12z UKMET were on the northwest
fringe of low tracks.  The 12z ECMWF slowed forward motion down
and matches better with its 00z ECMWF ensemble mean and
yesterday's 12z run. Given good agreement between the 12z Thu
ECMWF/12z Fri ECMWF and 00z ECMWF Ensemble Mean, 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/12z UKMET, 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 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-12z UKMET, 06z parallel GFS (FV3) and 00z ECMWF
ensemble mean.

The 00z-12z ECMWF have changed with the phasing of the upper low
west of Hudson Bay on Monday, with the 12z run further southeast
and closer to other solutions. The run to run variability leaves
confidence in either operational ECMWF run low. 

...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