Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
141 PM EST Mon Nov 26 2018

Valid Nov 26/1200 UTC thru Nov 30/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: General model blend
            More weight on 00Z ECMWF, less on 00Z CMC, 00Z UKMET
Confidence: Average

---19Z UPDATE---
No change to the preliminary preferences or reasoning. The models
generally maintained their 00Z model cycle differences relative to
each other, but there was some narrowing of the spread.

---PREVIOUS DISCUSSION---
Through the first 48 hours of the forecast, there is excellent
model agreement on the major synoptic features with tight
clustering of deterministic models and ensemble members. The
greatest uncertainty begins to develop on Wednesday as a trough
begins to amplify off the West Coast just to the east of the North
Pacific Jet extension. This may cause some downstream
amplification of the pattern as well, which is leading to much
larger ensemble spread by 30/00Z.

The model preference beyond 48h is weighted less toward the 00Z
CMC and 00Z UKMET which show notable differences with a downstream
shortwave trough over the Midwest on Thursday. The UKMET is
considerably faster, so it is almost completely out of phase with
the largest ensemble clusters, and the CMC is notably more
amplified. They also are indicating a more amplified shortwave
ridge over the Great Basin just ahead of the approaching trough.
Although they can't be totally ruled out, they do have less
ensemble support so less weight was placed on those models.

With the trough approaching the West Coast, model trends have been
limited thus far. There has been perhaps a slight trend toward a
stronger wave reaching the coast a little further south, a
forecast best represented by the ECMWF, ECMWF Ensemble, and NAM.
Many of the ECMWF Ensemble members are further south and stronger
with the wave than the GFS, CMC and UKMET, as well as most of the
CMC+GEFS members. There were also a few CMC+GEFS members closer to
the ECMWF Ensemble mean. Therefore, given the slight trend toward
a southward approach, and slightly more ensemble support, greater
weight was placed on the ECMWF forecast. However, a blend approach
is still preferred due to uncertainty.


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

Lamers