Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
145 AM EST Wed Jan 02 2019

Valid Jan 02/0000 UTC thru Jan 05/1200 UTC

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

00Z Model Evaluation...with Final Preferences and Confidence
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...Overall pattern across the CONUS...
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Preference: 00Z NAM/ECMWF/CMC blend
Confidence: Average

..07Z update...

The 00Z ECMWF/UKMET/CMC all nudged faster with the closed low
after reaching the lower Mississippi Valley (more so in the
UKMET), with the 00Z GFS/UKMET/CMC toward the faster side of the
middle of the latest ensembles and the 00Z NAM/ECMWF toward the
middle. The 00Z NAM is also toward the northern edge of the 00Z
deterministic models. While differences are relatively small,
prefer to stay toward the better trends/clustering supported by a
00Z NAM/ECMWF/CMC blend. Across the West, a similar quickening
trend was observed but the 00Z GFS continues to be fastest, with a
broad non 00Z GFS blend acceptable for the West. Otherwise, no
changes were noted nor recommended for changes.

...previous discussion follows...

Two defined streams of flow will be in place across the lower 48
with two systems to note within each stream through Saturday
morning. There is good model agreement with a northern stream
shortwave and related offshore surface low near the Northeast
Wednesday night/Thursday morning. A large closed low tracking
through the southern Plains on Thursday has continued to trend
slower and a bit south over the past three 12/00Z ensemble cycles
with only minor spread currently in place through Friday night.
The 00Z GFS remains toward the faster side of the deterministic
spread and the 00Z NAM ends up toward the northern side of the
guidance with its 500 mb low for Friday. A general blend, which
results in only a small contribution from the faster 00Z GFS is
recommended here.

Across the western U.S., a northern stream shortwave is forecast
to reach the Pacific Northwest Thursday night with the 12Z CMC
noted to be significantly faster than the remaining deterministic
consensus and relatively good ensemble clustering. The second
shortwave nears the West Coast Saturday morning with the ensembles
continuing to show differences mainly with the timing of this
feature. The GFS/GEFS lead the pack with a faster trough axis
progression but given past slowing trends noted near the lower 48
over the past several days and a majority of ensemble spaghetti
plots slower than the GFS, a weighting toward the middle/slower
side of the latest ensembles is preferred. This is best
represented by a blend of the 00Z NAM, 12Z ECMWF and 12Z UKMET.

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

Otto