Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1126 PM EST Wed Dec 12 2018

Valid Dec 13/0000 UTC thru Dec 16/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...

Preference: Blend of the 00Z GFS and 12Z ECMWF
Confidence: Slightly below average

The latest model consensus continues to support an impressive
amplification of the large scale pattern over the CONUS during the
next 36-48 hours, with ridges setting up over the West and East,
as a deep trough digs across the central and southern Plains and
then becomes cut off from the main belt of the westerlies through
Friday. By the weekend, this deep layer closed low will break down
the ridge across the East and advance east toward the central
Appalachians and Mid-Atlantic region. Meanwhile, a northern stream
trough will be progressively crossing the Great Lakes and
Northeast. In general, the models are showing rather good
agreement with the depth of the closed low, but there end up being
more substantial differences relating to the placement of the
height falls as the energy advances east. By Saturday, the 00Z NAM
and to a lesser extent the 00Z GFS are north of the 12Z CMC and
12Z ECMWF with the closed low track. The 12Z UKMET is very close
to the 00Z GFS solution at this point. The ensemble guidance is
split with the details of timing and placement as the GEFS suite
is more supportive of the northerly GFS/UKMET tracks, and the
ECENS suite is farther south and closer to the ECMWF/CMC camp. The
NAM has little support for its farther north evolution and will be
dismissed for the time being.

There will a secondary shortwave trough progressively advancing in
across the Pacific Northwest by Friday and then quickly advancing
downstream across the northern Plains and upper Midwest by Sunday.
The 00Z NAM/GFS and 12Z UKMET all tend to have a bit more
progression and interaction of the southern tail of this trough
with the downstream closed low lifting from the lower MS Valley to
the Mid-Atlantic region. The 12Z CMC is the slowest solution with
the secondary trough crossing the northern Plains and upper
Midwest. The preference at this point will be to compromise
between the southerly and northerly model camps relating to the
closed low, and also with respect to the timing differences seen
with the northern stream energy. Confidence is a bit limited, but
given the split global model camps, a blend of the GFS and ECMWF
should suffice for the time being.


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

Orrison