Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
201 AM EST Sun Jan 20 2019

Valid Jan 20/0000 UTC thru Jan 23/1200 UTC

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

00z Model Evaluation with Final Preferences
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...Eastern U.S...
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Preference: Any of the operational models
Confidence: Above average

A cyclone will track from the Mid-Atlantic states to offshore of
New England Sunday into Monday, driving a major winter storm over
interior locations and all of northern New England (including the
coast). Model solutions remain locked in with little spread on the
synoptic scale. The GFS continues to lean a little too progressive
in the upper air pattern across southern Canada, the Great Lakes,
and the Northeast U.S., but this does not make too much difference
until the end of Day 2 at which time precipitation will have ended
over New England.


...Western/Central U.S...
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Preference: Blend of the 00Z ECMWF/Canadian with some leeway to
employ the GFS
Confidence: Average

A broad but energetic trough of neutral to positive tilt will
enter the West Sunday and expand through the central U.S. to Great
Lakes region by Tuesday. There is some semblance of stream
separation, with distinct concentration of gradients over the
Northern Plains to Great Lakes and also from the southern Plains
into Mexico. Ensemble surface low clustering over multiple model
cycles has favored a low reaching lower Michigan by 23/12Z, and
the 00Z ECMWF/Canadian solutions best match the ensemble
consensus. The GFS is also close, but still leans a little faster
in the northern stream. Regarding the depth and speed of the
trailing southern portion of the trough, the ECMWF Ensemble Mean
has been trending deeper with each run at the base of the trough
over Mexico. The GEFS is somewhat less deep and shows no real
trend. Overall there seems to be enough model evidence to suggest
the 12Z ECMWF had been too deep and slow. The 00Z ECMWF trended
more toward a consensus solution with a little less depth and more
progression. This makes the 00Z ECMWF one of the better choices
for this system, although we note that the UKMET is hanging on to
something deeper and slower, so there remains some uncertainty.
The 00Z NAM, on the other hand, sets the more progressive edge of
the envelope with a faster surface front in the lower Mississippi
Valley. A lot of the model differences are smaller scale and in
the noise, but the NAM was fast enough at the surface and flat
enough aloft to be excluded from our preference although it may be
useful through Day 2.


...Pacific Northwest on Day 3...
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Preference: Blend of the 00Z NAM/GFS/UKMET
Confidence: Slightly below average

Somewhat messy pattern here by Day 3 as multiple flattening
shortwave troughs attempt to get through a mean ridge position,
bringing some rain into the Pacific Northwest. Structure of the
shortwaves differs greatly among the models, but general
clustering of solutions as well as arguments based on advections
would suggest the 12Z ECMWF was too fast to move the northern-most
shortwave through the ridge and into the northern Rockies by
23/12Z. Indeed, the 00Z ECMWF slowed down considerably, but also
became so washed out as to lose that northern-most wave up into
southeast Alaska. The 00Z Canadian represented another
particularly fast and flat solution. We prefer the reasonable
clustering seen between the NAM/GFS/UKMET, although noting that
confidence in the details is a little below average.

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

Burke