Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1136 AM 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: 12Z GFS/00Z UKMET/00Z ECMWF 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 12Z
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 12Z GFS, 00Z UKMET and 00Z 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 00Z CMC was noted as being somewhat
similar to the 12Z NAM with low tracks that are a bit north of the
model consensus. The CMC is also a little slower than the
consensus with the low evolution over the Northeast. Overall,
there is better ensemble support for the GFS/UKMET/ECMWF camp,
especially from the 00Z ECENS suite, although there were some 06Z
GEFS members that do support the NAM.

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 00Z UKMET begins to
outpace the model consensus a bit with its height falls and
surface low evolution. Meanwhile, the 00Z CMC begins to lag the
model consensus. 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 blend of the GFS/UKMET and
ECMWF 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