Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
251 PM EDT Wed Sep 12 2018

Valid Sep 12/1200 UTC thru Sep 16/0000 UTC

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

12Z Model Evaluation Including Preferences and Forecast Confidence
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...Pacific Northwest...
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Preference: 12Z GFS/GEFS mean and 12Z ECMWF blend
Confidence: Slightly Below Average

17Z Update: No significant changes to the preferred blend as the
12Z ECMWF trended towards the 12Z GFS/GEFS mean with amplification
and trend towards a deeper trough entering the NW on Saturday. The
UKMET and CMC are reasonable with the sharpening shortwave off
California late Saturday, but the northern stream vort energy
ejecting around the parent vortex continue to be too fast for an
intensifying longwave trough, so no change to the preferred blend.

Guidance continues to show increasing spread through 84 hours with
the reinforcing longwave trough across the Pacific NW. 12Z NAM
persists as the strong/fast outlier with its ejecting of mid-level
shortwaves around the parent vortex to the north, although the
UKMET is also on the fast/strong side with these features. This
leads to faster surface low development into central Canada, but
the primary cold front axis is relatively unaffected across the
Northern Plains. By Saturday night many of the operational models
are outrunning the ensemble means with the position of the
deepening trough centered just west of British Columbia. The
GFS/ECMWF are nearly identical and slower than the remaining
guidance, so will include them in the blend along with their
ensemble means to slow progression slightly.


...Troughs over southern and eastern Texas...
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Preference: Non-CMC blend
Confidence: Average

17Z Update: 12Z CMC continues to be the fast outlier with lifting
the trough into Texas early on Friday, while the remainder of the
guidance is about 12 hours delayed. Overall the guidance envelope
is pretty small so a non-CMC blend is still preferred.

Models are in reasonable agreement although the CMC remains quite
fast lifting the trough into Texas Friday and Saturday. This is
evident both in surface features and by westward displacement of
the max QPF axis. The UKMET is a bit faster lifting the surface
trough onshore as well, but within the guidance envelope and will
be included in the preferred blend. Please see the latest NHC
tropical weather outlook for development potential of this feature.

...Hurricane Florence...
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Preference:  See NHC forecast discussion
 Best Proxy: 12Z GFS/12Z ECMWF blend

Guidance is in close agreement through 36 hours before diverging
considerably thereafter. The NHC track is most closely followed by
an ECMWF/GFS consensus. Please refer to the latest NHC discussions
and products for more detailed information.

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

Weiss