Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1158 PM EST Mon Nov 26 2018

Valid Nov 27/0000 UTC thru Nov 30/1200 UTC

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

00Z NAM/GFS Evaluation...with Preliminary Preferences and
Confidence
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...Overall Pattern Across the CONUS...
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Preference: Non 00Z NAM blend, led by the 00Z GFS and 12Z ECMWF
Confidence: Average

Amplified mid-upper flow was in place at the beginning of the
short range period with troughing just off of the West coast,
ridging over the Intermountain West and a large closed low
centered over the Great Lakes region. Through Wednesday into
Thursday, the flow will become rather zonal across the lower 48
but a potent shortwave is expected to reach the coast of northern
California Thursday morning and amplify into the Four Corners
region Friday morning.

The largest differences stem from a potent shortwave approaching
northern California Thursday morning. The 00Z NAM trended
flatter/weaker with this feature and is not in agreement with the
ensemble clustering. Actually, the ensembles show a modest amount
of spread off of the West Coast, but the 00Z NAM is significantly
different and on the far edge of the ensemble guidance. Given the
lack of support for the 00Z NAM, it will not be included in the
preference.

Downstream to the east of the Rockies, a frontal wave is forecast
to track toward the middle Mississippi River Valley through Friday
morning but significant non-NAM model differences exist related to
the strength of a 700 mb shortwave. There are timing and amplitude
differences in all of the models regarding the low level
shortwave, but the 00Z GFS and 12Z ECMWF are rather similar and
match closest to a blend of the GEFS/ECMWF ensemble means.

The only area where the 12Z ECMWF is not favored is with a weak
frontal wave near northern North Dakota late Wednesday into
Thursday afternoon. It is here that there is decent ensemble
agreement with a wave of low pressure which is reasonably close to
a non-12Z ECMWF blend.

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

Otto