Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
204 AM EST Fri Jan 18 2019

Valid Jan 18/0000 UTC thru Jan 21/1200 UTC

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

Final 00Z Model Evaluation
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A major winter storm will affect the central and eastern United
States as low pressure tracks from Colorado Friday morning to the
New England coast by Sunday. Frigid cold will develop behind the
storm in the central and east, while weather in the West remains
active.

...Central and Eastern CONUS...
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Preference: Blend of the 00Z GFS/ECMWF/Canadian
Confidence: Slightly Above Average

Energetic southern and northern stream troughs will eventually
phase, yielding a full latitude trough along the east coast by
Sunday. A well defined surface low will track from Colorado early
Friday to the New England coast by 12Z Sunday. Model spread is
relatively small, although slight errors in track will translate
to significant forecast challenges regarding precipitation type
and amount. Over the past couple of model cycles the GFS and ECMWF
have been fairly steady and are each supported by their respective
ensembles. The differences between the two camps narrowed a bit on
the 00Z cycle, with the ECMWF moving the trough just a hair faster
than it had been. The 00Z Canadian also clusters well with the
GFS/ECMWF. The NAM looks good through Day 2, but then leans to the
fast side of the envelope both aloft and at the surface on Day 3,
Sunday into Monday.

...Western CONUS...
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Preference: Blend of the 00Z GFS/ECMWF/UKMET/Canadian
Confidence: Average

The pattern over the West is a little more straight-forward, with
the gradual progression of an open, medium wavelength Pacific
trough into the West during Days 1-3. Such a system is usually
modeled fairly well, but the flow is energetic, and still with
some semblance of northern and southern stream components to
complicate matters. The 12Z UKMET was wildly out of phase with the
ensemble majority, and the 12Z Canadian as well as 00Z NAM
appeared too flat given the wavelength spacing and ensemble
consensus. This had left the GFS/ECMWF as the preferred options,
but 00Z runs of the UKMET and Canadian trended favorably toward
the GFS/ECMWF-led ensemble consensus. Thus, the only model not
really falling nicely in line was the NAM with its particularly
flat wave by Day 3 over the Great Basin / Four Corners.

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

Burke