Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
307 AM EST Fri Jan 04 2019

Valid Jan 04/0000 UTC thru Jan 07/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
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***Overall Pattern Across the CONUS***
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Preference: General model blend
Confidence: Slightly above average

08z update: With the rest of the 00z guidance now in, the biggest
model differences remain across the Western US as a longwave
trough approaches the region on Saturday into Sunday. While there
is good agreement in a surface low approaching the northern CA,
southern OR coast, once it moves inland, the models struggle with
how fast it moves up the coast into B.C. The ECMWF is on the
slower side of the model spread, while the GFS and NAM are on the
faster side. Another system quick to follow late Sunday into
Monday has some speed differences as well, with the usual fast GFS
bias showing up. Given some of these spatial and temporal
differences, a general model blend is still preferred across the
CONUS.

---previous discussion---
A closed mid/upper low currently over the Arklatex region will
track across the southeast US then northeast into the Mid-Atlantic
and off the Northeast US coast while a northern stream shortwave
moving through the Great Lakes will be the main driver to help
push it off the coast by 06.00z. There is very good model
agreement in the mid/upper level mass fields across the eastern US
such that a general model blend of the available guidance would
suffice. At the surface, a low pressure will lift through the TN
and OH Valleys then off the coast of the Mid-Atlantic. Once that
system passes, general ridging will encompass much of the eastern
US while longwave troughing develops across the western/central
US.

For the Western US, the next weather system to impact the region
will be Saturday as a longwave trough approaches the west coast. A
compact surface low is expected to push onshore the northern
California or southern Oregon coast and bring widespread moderate
to locally heavy precipitation. Compared to the past 12-24 hours,
there is slightly better model agreement with the speed and
location of the surface low as it pushes onshore Saturday. The GFS
continues to be somewhat faster compared to the rest of the
models, but its difference is not as large as it was before. By
the end of the forecast period (07.00z), another shortwave is
likely to move into parts of the Pacific Northwest. The GFS is
more amplified compared to the ECMWF with this feature as it moves
into Washington State. For now, a general model blend is preferred
for the CONUS this cycle. 

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

Taylor