Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1138 AM EST Fri Jan 04 2019

Valid Jan 04/1200 UTC thru Jan 08/0000 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: Blend of 12Z GFS and 00Z ECMWF
            Increasingly weighted toward the ECMWF after 06/12Z
Confidence: Average

There is not a tremendous amount of spread in the model mass
fields over the next several days, however there are some
important differences that will make an impact on the placement
and intensity of precipitation. In general, a blend of the 12Z GFS
and 00Z ECMWF offers a forecast with relatively strong ensemble
support that represents a reasonable consensus.

The greatest differences emerge as a result of variability with
the upstream wave train over the Pacific. Available deterministic
models are fairly similar with a trough arriving on the West Coast
Saturday Night, but show greater variability with a secondary wave
arriving about 12 hours on Sunday. The 12Z GFS offers a more
amplified secondary trough despite its position between a strong
trough near 140W and the initial wave kicking into the Plains.
Significant trough amplification between the two primary waves
seems less likely, and there is more ensemble support for a
flatter flow pattern in between. Therefore, the preference is
trended toward the ECMWF by Sunday.

Other smaller differences from other models have excluded them
from the preference at this time. The 12Z NAM joins the GFS in
positioning the low off New England further south relative to the
other deterministic models and many of the non-NCEP ensemble
members. The preference with that low is to lean away from the
NAM/GFS in terms of precipitation placement. And the NAM
eventually flattens out the flow over the CONUS more than other
models, leading to differences in precipitation timing and
placement. The 00Z CMC and UKMET are near the outer edge of some
of the ensemble spread -- the CMC with the strength of the ridge
in the Southeast by Monday, and the UKMET with the amplitude of
the trough in the Plains at the same time.

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

Lamers