Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1208 PM EDT Wed Jul 18 2018

Valid Jul 18/1200 UTC thru Jul 22/0000 UTC

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

12Z model evaluation including preference and forecast confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference in Eastern US: 00z UKMET/ECMWF blend
Confidence: Slightly below average

Preference in Pacific NW US: 00z ECMWF/12z GFS blend
Confidence: Average

...Overall Model Analysis for the CONUS...

Models continue to show the greatest differences with a trough
digging into the Upper Midwest by late in the week, with the NAM
standing out from the main deterministic suite, being faster and
closing off a new upper level center in the Ohio Valley by Sat
into Sun.  The GFS and UKMET trend this direction (GFS faster)
while the ECMWF/CMC slide more eastward as the older center
broadens over the Central Great Lakes.  If you will, a typical
timing orientation only exacerbated by the larger spreads.  This
timing/strengthening also draws the warm conveyor belt and
associated shortwave out of the eastern Gulf of Mexico, with
moderate spread.  The NAM/GFS are quick and tucked further west to
the coast compared to the ECMWF/UKMET and CMC.  The further
eastward shift, allows the CMC to be quite amplified due to
orientation with the upper jet/divergence maxima, making it a bit
less desired at this point.   The catalyst for the model spread
appear to be related to the strength/magnitude of upscale feedback
from convection development this evening over the Mid-Missouri
River valley.  The NAM develops a complex that digs
south-southeast across NEB toward the Low MO-Valley today, with a
stronger 3H jet rounding the base of the trof earlier.  This is
followed by the GFS and so on... the Hi-res CAMs would suggest
that the NAM is an outlier but modest spread including within the
HREF mean/NBM (at least in QPF fields) suggest a compromise
between the UKMET and ECMWF may be a good suggestion, but at lower
(slightly below average confidence).

Further west, the closed low in the Gulf of AK reaches central BC
by late Fri with good agreement, the spread begins to increase
based mainly on if/how far east the main inner core before it
breaks down a bit and stretches in the ridge weakness over the
west coast (in the larger scale).  Timing, once again, becomes the
main difference though compact/vort centers, manifest as well. 
The NAM is fast and the UKMET is very compact with the trailing
shortwave.  The CMC is slow to stretch, while the ECMWF/GFS are
more inline with each other and the ensemble suite (trends in the
day to day ensemble suite) that would suggest a better overall
blend.  Confidence is average for this area.

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

Gallina