Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
233 PM EDT Mon Aug 13 2018

Valid Aug 13/1200 UTC thru Aug 17/0000 UTC

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

12Z model evaluation including preference and forecast
confidence...
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...Overall Synoptic Pattern across the CONUS...
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Preference: 12Z GFS/ECMWF blend
Confidence: Slightly above average

There is strong model agreement with many of the main features
across the CONUS and southern Canada, including the
exiting/devolving closed low over the Mid-Atlantic into the
Northeast, the weak trof off the Pacific Northwest coast and the
fast moving positive tilt trof/frontal zone crossing southern
Canada.  There is even solid agreement with the closed low over in
the lee of Rockies in the Southern Plains with respect to
timing/tracking of the low as it opens and the surface wave as it
lifts north into the Great Lakes.  The difference in the mass
fields appear to be the placement of the larger scale trof by Wed
into Thursday over the Northern Plains or Great Lakes; either
favoring the aforementioned wave lifting north or the tail end of
the fast moving Canadian trof that breaks off and becomes a
compact vorticity center over MT by Wed.  The 00z ECENS mean,
00z/12z ECMWF and the 12z GFS continue to be stronger/more compact
with the trailing wave over MT, favoring to shear/weaken the wave
a bit more in the Great Lakes aloft compared to the 12z
NAM/CMC/UKMET and GEFS mean which favor stronger/eastward shift of
the synoptic wave/height falls, with the 12z NAM first to break
from the consensus.   Even though the latter have the upstream
wave, it seems weak given the overall pattern should favor the
GFS/ECWMF/ECENS mean; faster flow north of the boarder and large
blocking wave slowly decaying downstream allowing for
slowing/vortex compaction/roll-up.   The overall impact to the
sensible weather/timing of the front is minor, especially as the
guidance phases together in the early medium range, so confidence
is moderately high (slightly above average) in a 12z GFS/ECMWF
blend (representing the ECENS mean/continuity); as well as the
GFS/ECMWF representing the other main CONUS features. 

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

Gallina