Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1145 PM EST Mon Dec 10 2018

Valid Dec 11/0000 UTC thru Dec 14/1200 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: 12z ECMWF/UKMET, 00z GFS
Confidence: Average

There are two areas of uncertainty in the forecast period across
the CONUS. The first lies with the digging wave across the central
US that is expected to form a closed low over the southern Plains
by Thursday. In the last few model cycles, forecast spread has
lessened, increasing confidence somewhat as the models seem to be
coming together with respect to earlier spatial and temporal
differences. The ECMWF remains the most occluded and thus slowest
of the solutions, though the rest of the available guidance in the
00z cycle (GFS, NAM) is not significantly ahead. At least aloft in
the 500 mb heights, a general model blend would suffice. At the
surface, with the closed low slowing, the surface low occludes
further west, now more over the Arklatex region and is also much
slower to progress north/northeast. Through the forecast period
(84 hrs), the spread is not as large as it was in earlier cycles.
Just beyond the period, there are considerable differences in how
quickly it kicks out toward the Appalachians and Mid-Atlantic
region. The CMC seemed to be too fast pushing the low to the
northeast. Overall, a blend of the 12z ECMWF, 00z GFS, 12z UKMET
seems appropriate.

The other area of forecast uncertainty is back across the Pacific
Northwest. By Thursday night into Friday, another strong shortwave
trough is expected to push right into Washington state. Here, the
models differ considerably on timing, with the 00z GFS/NAM being
the fastest and the 12z UKMET is significantly slower (the 12z
ECMWF/CMC lie in between). The 12z UKMET also is much stronger and
digs the wave deeper across the Pacific, owing to the stronger
ridging downstream (likely due to the closed low over the southern
Plains). This seems to be an outlier and is not preferred at all.
To account for the typical model biases, the preference will be
the 12z ECMWF/CMC solutions with some weight given to the slightly
faster 00z GFS. 


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

Taylor