Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
154 AM EST Sat Jan 19 2019

Valid Jan 19/0000 UTC thru Jan 22/1200 UTC

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

Final 00Z Model Evaluation...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A cyclone tracking through the eastern U.S. will produce a major
winter storm from the Midwest to the Northeast and heavy rain and
strong thunderstorms farther south. An arctic blast moves in
behind the storm in the central and east while a second weather
system keeps things unsettled in the West.

...Eastern U.S...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the operational models
Confidence: Above Average

Two well defined medium to long wavelength systems in a
trough-ridge-trough pattern will migrate across the country, one
producing a major winter storm in the East, and the other keeping
the West unsettled. Systems of this scale should be modeled fairly
well, and spread among the operational models is proving to be
minimal now that they have converged a bit more as to the details
of stream phasing over New England this weekend. In handling this
system, the NAM holds the cold air in place a bit more,
suppressing the surface low track slightly south and east of
consensus. This is a viable solutions worth considering,
especially as the global models have a tendency to scour the cold
air too readily. This is particularly true of the GFS, which in
this case is just a tad warmer than consensus in the low level
thermal fields over New England. A consensus blend should get at
the most likely solution while keeping in mind the colder NAM with
its sharper frontal zone is a real possibility.


...Western U.S...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 00Z NAM/GFS/UKMET
Confidence: Average

A trough with neutral to positive tilt will move more bodily
onshore late Saturday and progress steadily Plains and southern
Rockies by Tuesday. Operational guidance has been in good
agreement, but there is some run to run variability. The 00Z
Canadian moves a little out of phase with consensus aloft, and
produces a stronger surface low far to the north in the Plains on
Day 3. The ECMWF also made a stark trend in another direction,
with a colder pocket of air at the base of the trough over the
southern Rockies on Day 3 - delaying progression of the front
downstream over the central Plains. Overall consensus across
multiple model cycles would suggest leaning toward the cluster of
the NAM/GFS/UKMET.

Meanwhile, a flat wave could sneak through mean ridging to bring
rain back to the Pacific Northwest on Day 3. Guidance is a little
more chaotic with the details of the flat wave, but all generally
produce warm advection and some precipitation approaching western
Washington Monday night.

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

Burke