Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
227 PM EDT Tue Aug 14 2018

Valid Aug 14/1200 UTC thru Aug 18/0000 UTC

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

12Z model evaluation including final preferences
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...Overall Synoptic Pattern across the CONUS...
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Preference: General model blend
   Exclude: 12z CMC in Pacific Northwest
Confidence: Above average

19z update: The 12z UKMET backed away from the over-deepening in
the Great Lakes to Northeast on Day 3 and the ECMWF/CMC, like the
NAM/GFS trended a bit weaker/faster for much better overall
alignment.  The only significant mass difference remains with the
12z CMC in the Pacific Northwest being too deep; the UKMET may be
a shade fast toward the end of the forecast period but still
within ensemble spread to keep within the blend.   As such above
average confidence in a general model blend throughout the CONUS
with exception of the 12z CMC in the Pacific Northwest.

---Prior Discussion---
The overall synoptic pattern matches remarkably well especially
with the closed low over the Northeast slowly opening up and
sliding into southeast Canada by Thurs.  The remaining systems
show some model divergence but overall is fairly minor all
considered.   The largest discrepancy remains with the closed low
in the Central Plains lifting into the Great Lakes (and the
upstream kicker wave currently in W MT.  Here the 12z NAM/GFS were
a bit weaker and slightly faster than prior runs but match fairly
well with the deeper/slower 00z ECMWF/CMC, until late on Fri.  The
NAM/GFS may be onto a trend given the weaker/stacked upper low
currently in the central Plains.  Still, by 16/18z, the UKMET is
already showing signs of over-deepening the low and braking
left(north and west) of the tighter consensus; this also delays
the eastward march of the upstream wave leading to some timing
difference too. Both concerns appear opposite of the overall trend
and observations may suggest.  At this point, will support a
non-UKMET with these two systems.

Further west, the CMC shows a typical characteristic of a deeper
solution than the other guidance with the wave entering the
Pacific northwest by Fri.  The 12z GFS/00z UKMET and 00z ECMWF
show the best agreement in amplification of the wave, while the
NAM is a bit less wound up having shed some energy further north
into BC/Alberta.   Overall a general model blend may work, but
trends/ensembles suggest a non-CMC solution may provide the better
overall solution/tighter blend at higher confidence.


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

Gallina