Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
144 PM EST Tue Nov 20 2018

Valid Nov 20/1200 UTC thru Nov 24/0000 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
Confidence: Above average

The current pattern across the CONUS is rather amplified with a
deep layer ridge over the Intermountain West and a longwave trough
downstream across the Eastern U.S. Meanwhile, a longwave trough is
also positioned just off the West Coast with a separate southern
stream closed moving across southern CA.

The latest guidance strongly agrees that an area of low pressure
lifting up along the New England coast will deepen further through
tonight and lift through the Canadian maritimes through Wednesday.
In its wake, there will be another digging shortwave trough and
associated low pressure which will drop across the Great Lakes
region tonight and the Northeast through Wednesday. An anomalously
strong high pressure in its wake will bring near record cold to
the Northeast U.S. for Thanksgiving.

Across the West, the guidance is in excellent agreement depicting
the deep layer ridge breaking down and the offshore trough
advancing east and well inland through Thanksgiving. This will set
the stage for a well-defined atmospheric river event to impact the
Pacific Northwest and especially northern CA. A series of
shortwave impulses upstream will follow suit and arrive going into
Friday which will result in a multi-day heavy precipitation event.
The lead trough axis will advance downstream across the Plains and
MS Valley by Friday. Meanwhile, the southern stream closed low
over southern CA is expected to advance downstream and deamplify
into a progressive shortwave that will traverse the southern tier
of the nation.

The models are in very good agreement with the large scale
features overall across the CONUS, and based on the latest trends
and model clustering, a general model blend will be preferred
across the CONUS.

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

Orrison