Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1211 PM EST Wed Nov 28 2018

Valid Nov 28/1200 UTC thru Dec 02/0000 UTC

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

12Z NAM/GFS Model Evaluation...with Preliminary Preferences and
Confidence
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...Overall Pattern Across the CONUS...
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Preference: Blend of 12Z GEFS/00Z ECMWF/ECENS
Confidence: Slightly below Average

First, the low off New England strengthens in place near
Newfoundland Thursday with little differences in mainly light
precipitation Day 1 among guidance before shifting away from the
CONUS.

A strong shortwave trough approaches the CA coast tonight and is
the main weather maker through the period as it shifts to the
central CONUS. Differences begin on Day 2 with the 12Z GFS/06Z
GEFS mean closing off a low at H5 over the Great Basin - a full 24
to 36 hours before the rest of the Global guidance which wait
until the axis is east of the Rockies. Despite the earlier
closing, the 12Z GFS is not as deep with the low on Day 3 which
allows a more progressive track and is the main cause of
differences among the guidance. However, the 12Z GFS continues a
trend of less progression with recent GFS runs, so hopefully that
trend continues. That said, the deep low in the 00Z ECMWF is the
slowest solution. The ensemble means for both systems are similar
to the operational with timing being the main difference. A
compromised blend of the 12Z GFS leaning toward the EC solution is
recommended in the model preference.

A second shortwave of note will reach the Pacific Northwest-Friday
night into Saturday. The differences here are mainly due to the
strength of the east Pacific ridge extending into the Gulf of
Alaska. The 00Z ECMWF is stronger with this ridge and closes it
into a high quicker (looking ahead into Day 4/5) which will allow
for more shortwave activity into the Pac NW. However, a general
model blend is appropriate through Day 3 given similar timing and
extent of precip across the west.

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

Jackson