Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1238 AM EDT Sat Sep 08 2018

Valid Sep 08/0000 UTC thru Sep 11/1200 UTC

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

12Z model evaluation...with preferences and forecast confidence
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...Overall Synoptic Pattern across the CONUS...
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Preference: General model blend
 Exception: 00z GFS and 12z UKMET/ECMWF blend in E WA/N ID/MT
after late Mon
Confidence: Slightly above to above average

The remnants of Gordon are currently phasing with the baroclinic
zone across MO, and as the mid-level wave continues to amplify the
combination of the tropical/front will deepen across the Ohio
valley into the central Great Lakes before weakening/shearing into
the increasingly confluent flow in Southeast Canada.  The 12z
UKMET is a bit more amplified/occluded than the other guidance,
but is not terribly out of position within a larger blend.

Elsewhere across the CONUS, the mass fields are fairly congruent
and blend nicely.  The main spread remains mostly within central
Canada with the lead wave that is currently progressing through
the Pacific NW/southern Canadian Rockies.  There has been a trend
for the faster/stronger solutions presented by the 00z NAM/12z
UKMET to trend back toward the more consistent GFS/CMC/ECMWF
solutions as the surface wave develops in the lee of the terrain
across MT into S Canada, the trof/frontal zone draping back into
the Northern tier is agreeable enough with the ensemble suite to
support a general model blend even as it progresses into Day 3
across Ontario/James Bay.

The frontal zone will remain near the boarder and lift further
north into Canada as the lead height-falls/shortwave from the
closed upper low off Vancouver, crosses the Rockies and spurs
another lee cyclone in S Alberta/Saskatchewan/Montana by 00z Tues.
  The timing is fairly good, with exception of the 00z NAM which,
like the prior system is fast and outpaces the
ensemble/continuity.   Other differences, manifest in
timing/interaction with digging Arctic stream late Monday/Tues. 
Here the CMC is very slow (even for its typical slow
bias)...making a deeper surface wave and stronger cold front push
in the northern tier.  As such a 00z GFS and 12z UKMET/ECMWF blend
would appear best on day 3 for northern tier forecasts.  So all in
all, a general model blend can be afforded across the CONUS at
slightly above to above average confidence with the small
exception of MT on Monday/Tuesday toward a 00z GFS and 12z
UKMET/ECMWF blend.


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

Gallina