Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
206 PM EST Thu Jan 17 2019

Valid Jan 17/1200 UTC thru Jan 21/0000 UTC

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

12Z Model Evaluation...with Final Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Amplified flow will be in place across the lower 48 through the
weekend. A strong mid-upper level trough will track from the
western U.S. today to the eastern U.S. for Sunday corresponding
with cyclogenesis across the central U.S. late Friday. Meanwhile,
the Pacific Northwest will experience a series of shortwave
troughs through Sunday with a landfall Friday night and Sunday
morning.

...Central and Eastern CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 12Z NAM/12Z ECMWF blend
Confidence: Average

...19Z update...

The 12Z ECMWF/UKMET/CMC continued the faster trend across the
Mississippi Valley into the East with the mid-level trough axis,
but not to the degree of the 12Z GFS. The 12Z CMC is the next
fastest with generally good agreement now with the 12Z
NAM/ECMWF/UKMET.

...previous text below...

Ensemble and deterministic trends have been notably faster with
the trough progressing through the central and eastern U.S. this
weekend and while the latest ensemble agreement is modest, the
faster 12Z GFS is not an outlier, but the differences may be tied
to a northern stream shortwave over the Great Lakes region
Saturday to Sunday. The Great Lakes shortwave shows a bit more
progression in the 12Z NAM/GFS compared to the 00Z ECMWF/UKMET/CMC
on Sunday with trends converging nearer to the slower solutions up
north. Currently, the 00Z ECMWF is in great agreement with the
latest ensemble means, but given the faster trends over the past 3
cycles, prefer to be a bit faster than the latest means, with a
blend of the 00Z ECMWF with the 12Z NAM and perhaps some 12Z GFS
toward late Sunday off of New England lying close to ideal at this
time.

...Western CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 12Z GFS/12Z ECMWF blend
Confidence: Average

...19Z update...

Similar timing differences remain with the shortwave to impact the
Northwest early Saturday as with the earlier guidance discussed
below. Regarding the second shortwave for Sunday, relative to
their 00Z cycles, the 12Z UKMET sped up...the 12Z ECMWF and 12Z
CMC slowed down. Considering the latest guidance, there is no
change in the amount of spread with a GFS/ECMWF blend still
considered the best solution that falls toward the middle of the
latest spread.

...previous text below...

Across the West, the latest ensemble clustering has converged
closer to a 00Z ECMWF/12Z GFS blend compared to the slower/farther
west 00Z CMC and 12Z NAM. This applies to the shortwave/surface
low nearing the British Columbia coast early Saturday morning.
Timing differences continue with a second shortwave nearing the
Pacific Northwest coast Sunday, with the 12Z NAM/GFS slower and
00Z ECMWF/UKMET/CMC faster. Ensemble means support a solution in
the middle given no clear timing trends in the ensemble guidance,
only slightly more amplified.

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

Otto