Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
239 PM EDT Sun Aug 26 2018

Valid Aug 26/1200 UTC thru Aug 30/0000 UTC

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

12Z Model Evaluation and Preferences with Confidence
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...Overall Synoptic Pattern across the CONUS...
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Preference: Model consensus minus the NAM
Confidence: Slightly above average

For the majority of the larger-scale features, a model consensus
could be used to mitigate minor wave timing/amplitude differences.
That includes the 12z GFS, 00z UKMET, 00z ECMWF and 06z GEFS Mean.
 As the mid-upper trough axis moves from Plains into the
Mississippi valley late Tue-early Wed, recommend given the least
amount of weight to the Nam ,
which is an outlier on the magnitude of the 500 mb trough that
eventual develops into a closed low while other models have a more
progressive open wave.

The GFS has trended towards a slightly less amplified wave, which
on Wed leads to a faster sfc low moving along the front from Lake
Huron into southeast Canada.
The NAM/ECMWF/UKMET clustering better with slower motion, along
with the 06z GEFS Mean.
Consequently, odds are the GFS may be too fast with the timing of
the wave across the Great Lakes into southeast Canada Wed. 

The 12z ECMWF changed the phasing and timing of the 700 mb wave
that resulted in the axis of low pressure shifting south in Maine
on day 3 and the front slower to move across the mid west.  Given
the 00z ECMWF mean matches the 12z GFS/GEFS/UKMET better, low
confidence
exists in the adjustments made in the 12z ECMWF.

The models cluster well with a forming 700 mb closed low that
drifts off the northern CA coast, and then a wave crossing
Vancouver Island towards the Pacific northwest, with a surface low
and front forming in WA/OR.

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

Petersen