Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1028 AM EST Tue Dec 18 2018

Valid Dec 18/1200 UTC thru Dec 22/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Central/Eastern US...
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Preference: 00z ECMWF, 06z GFS, 12z NAM blend
Confidence: Average

The upper level pattern will become increasingly more amplified
over the central/eastern US through the forecast period. A
deepening trough over the central US will take on a negative tilt
by Thursday night, potentially closing off a low near the southern
Gulf Coast, then become even more negatively tilted as it lifts
through the mid-Atlantic region. In general, the deterministic and
ensemble guidance show good agreement spatially and temporally.
The 06z GFS solution remains the strongest, closing off at 500 mb
earliest (across the Arklatex region) while the rest of the models
stay open. The surface fields show more variability, particularly
with the track and speed of a low that will move up the east
coast. Here, the 00z CMC is too fast and too deep. The UKMET is a
bit to the west of the consensus, while the NAM is also fast, but
generally to the right. The 00z ECMWF and 06z GFS are not too
different in both spatial and magnitude terms, so for this cycle,
a blend of the GFS and ECWMF would suffice.


...Pacific Northwest...
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Preference: 00z ECMWF, 06z GEFS blend
Confidence: Below Average

A pair of shortwave trough will push onshore across the Pacific
Northwest through the forecast period. The first will arrive later
tonight into Wednesday morning. Following that feature, some
ridging will develop ahead of a positively tilted trough that will
push into the region Thursday night into Friday. Aloft, the mass
fields are in reasonable agreement across the deterministic and
ensemble guidance with respect to speed and magnitude. The biggest
differences are at the surface, which advertise a deepening low
moving across either extreme northern Washington state or southern
British Columbia. The 06z GFS, 12z NAM are considerably faster,
bringing the low onshore as early as 20.12z while the non-NCEP
solutions are actually clustered together very well but almost 12
hours slower. The GFS seems to be too fast, where the operational
solution is faster than the GEFS mean. So for this cycle, prefer
to go with a compromise blend at this point, with the 00z ECMWF
and 06z GEFS mean. The CMC is the slowest of the group and like
the previous discussion mentioned, it is likely too slow and was
not considered for 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