Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1131 PM EST Mon Jan 21 2019

Valid Jan 22/0000 UTC thru Jan 25/1200 UTC

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

00Z Model Evaluation with Preliminary Preferences
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...Developing Broad Cyclonic Flow Rockies and Eastward...
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Preference: 00Z GFS

A cold front and pronounced shortwave trough will push out of the
Rockies and toward the East Coast through Thursday, followed by a
northern stream arctic intrusion that will carve out a deep and
broad scale cyclonic flow regime by Friday morning. The models
arrive at a similar pattern by Day 3, but with numerous detail
differences during the earlier periods. Models have been
struggling from run to run in depicting the amplitude of a frontal
wave and brief mid level closed low over the central Plains. This
leads us to trust the shorter term trends seen in the 00Z NAM/GFS
with the system now fully in the upper air network. These models
trended toward a sharper wave forming in vicinity of Kansas early
Tuesday. This slows the frontal progression which had earlier been
though to be too fast in the NCEP guidance. Perhaps the best
center point for several model cycles has been the ECMWF Ensemble
Mean, and now the 00Z GFS is reasonably close to that while also
being more trustworthy with the short term details over the
Plains. The NAM looks a little squirrelly, with suddenly very cold
heights over the southern High Plains early Day 1, and then an odd
eastward shove on the surface low over eastern Canada by Days 2/3
- so we will not have the NAM in our preference, but it could be
useful in some areas.


...Pacific Northwest...
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Preference: Blend of 00Z NAM/GFS

Numerous low amplitude shortwave troughs are set to cut across the
top of a mean ridge position off the West Coast, and move into the
Pacific Northwest the next few days. The shortwave details carry a
good deal of uncertainty, but model and ensemble clustering as
well as run to run continuity have generally favored the NCEP
guidance relative to the ECMWF the past few cycles.

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

Burke