Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1149 PM EST Sat Jan 05 2019

Valid Jan 06/0000 UTC thru Jan 09/1200 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: General model blend
Confidence: 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 US Sunday
into Sunday night while a series of troughs push across the
western US into the central Plains which is expected to phase and
become a deeper longwave trough over the eastern US by Wednesday.
At the surface, a low will develop across the central Plains then
lift into the Great Lakes then will redevelop/deepen off the New
England coast Tuesday night into Wednesday.

The biggest differences noted in the guidance lies with the 00z
NAM and the strength of the trough developing across the Great
Lakes into the Northeast Tuesday night into Wednesday. The NAM is
considerably sharper/stronger compared to the global models and
also lies on the faster spread compared to the GFS/ECMWF. Its
surface depiction across southern Canada is on the northern end of
the model spread. In the previous cycle, the GFS was a bit
deeper/stronger, but with the 00z GFS those differences seem to
have been resolved, or at least not as prominent.

Right at the end of the forecast period /09.12z/, a surface low
developing off the New England introduces quite a bit of forecast
uncertainty and possible precipitation impacts. How quickly the
trough phases and becomes negatively tilted will dictate where the
low develops off the coast and how strong before it pulls away.
There are signals of an inverted trough hanging back to produce
precipitation. The NAM is further north compared to the ECMWF/GFS,
which are actually in decent agreement. The CMC is further east
while the UKMET is an outlier to the west. Here, a blend of the
GFS/NAM/ECMWF with more weight to the consistent ECMWF and its
ensemble mean is preferred.

Elsewhere, the models all agree in having a rather formidable
large scale ridge over the Western U.S. by the end of the period
as a deep closed low and associated longwave trough evolves
offshore of the West Coast. All of the models show a rather strong
surface low center as well with these strong height falls, but the
NAM is south of the global model consensus with the positioning of
its low center surface and aloft. The global models are well
clustered with the depth and timing of this energy and have
excellent ensemble support from the GEFS and ECENS suites.

Based on the comparisons above, a general blend should suffice for
the larger scale mass fields, noting some of the model differences
across New England late on day 3.


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

Taylor