Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
156 PM EST Sun Jan 06 2019

Valid Jan 06/1200 UTC thru Jan 10/0000 UTC

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

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

...Overall Pattern Across the CONUS...
Preference: Non-NAM blend...Eastern U.S.
            General model blend...Western U.S.
Confidence: Slightly above average

In general, the model guidance is in good agreement with the large
scale pattern across the CONUS through the forecast period. A
quick-moving shortwave trough will skirt the Northeast through
tonight while a series of shortwave troughs push across the
Western U.S. and out across the central Plains which are expected
to phase and become a deeper longwave trough over the Eastern U.S.
by Wednesday. At the surface, a low will develop across the
central Plains and lift into the Great Lakes through Monday, but
then a new area of strong cyclogenesis will occur in across the
Northeast and coastal areas of New England Tuesday through
Wednesday as the aforementioned phasing occurs.

The biggest differences noted in the guidance lies with the NAM
and the strength of the trough developing across the Great Lakes
and into the Northeast Tuesday night into Wednesday. The NAM is
north of the model consensus with its height fall evolution over
the Northeast, and prior to this, it tends to be a bit deeper than
the global models as energy traverses southern Canada. Its surface
low depictions across southern Canada and also with the strong
cyclogenesis over the Northeast are on the northern end of the
model spread. The global models as led by the GFS, UKMET, CMC and
ECMWF are in very good agreement with the height fall evolution
ejecting east across the Midwest, southern Canada and the
Northeast along with their respective surface low plots including
the deep low center near New England by Wednesday. The UKMET
though is now noted as being a tad weaker than the model consensus
with the deep low evolution near New England on Wednesday, but is
not the outlier solution like the NAM is depicting. Overall, there
is better ensemble support for the non-NAM global model consensus.

Elsewhere, the models all agree in having a rather formidable, but
transient large scale ridge over the Western U.S. by Tuesday which
then breaks down as a deep closed low and associated longwave
trough evolves offshore of the West Coast and ejects northeast in
across the West Coast and especially the Pacific Northwest. All of
the models show a rather strong surface low center as well with
these strong height falls. The guidance is in fairly good
agreement through Tuesday with their mass field solutions, but
thereafter there is some timing spread as the CMC begins to lag
the model consensus with the height fall and surface wave
evolution. The latest GEFS and ECENS suites support a general
model blend led by the deterministic GFS and ECMWF solutions.

Thus, based on the comparisons above, a non-NAM blend will be
favored across the Eastern U.S., with a general model blend across
the Western U.S., which includes the evolution of the deep low
center off the West Coast, although a bit more weighting to the
GFS/ECMWF camp can be afforded.


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

Orrison