Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
334 AM EDT Sat Sep 28 2019

Valid Sep 28/0000 UTC thru Oct 01/1200 UTC

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

00Z Final Model Evaluation with Preferences and Forecast Confidence
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...Northwest...
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Preference: General Model Blend through 60 hours
    ECMWF/ECENS/GEFS Day 3
Confidence: Above average

07Z Update:
The guidance is in general good agreement with the evolution of a
significant trough across the Northwest. Timing and spatial
differences crop up after 60 hours /Monday/ with respect to the
slow filling of the trough and how it may begin to shear to the
northeast. However, model differences have weakened with the full
00Z suite. For consistency, will make no changes to the preferred
blend from previous as there has been good run-to-run consistency.

Previous Discussion:
The general model spread through Day 2 remains quite minimal with
the position and intensity of an anomalous closed low across
WA/OR. As the low begins to evolve by opening and ejecting to the
northeast, the spread increases drastically such that by the end
of the forecast period there is quite a bit of spatial
uncertainty. The GFS ejects the closed low much faster than the
remaining guidance, which is both not consistent with its ensemble
mean, but also unlikely based on the strength of the Pacific Jet
streak digging southward from Alaska. The CMC is too quick to push
the entire trough axis to the east and tilt it neutral, well out
of tolerance with the global consensus keeping the longwave trough
positively tilted and hung back towards California. The ECMWF and
its mean show the most consistency, and are in very good agreement
with the GEFS mean. This solution also seems more reasonable than
a faster push of the trough to the E/NE as jet energy continues to
dig southwards off the PacNW coast.


...Rest of CONUS...
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Preference: General Model Blend through 60 hours
    Non-CMC Day 3
Confidence: Slightly above average

07Z Update:
The previous amplitude and spatial issues with a shortwave moving
near New England Monday night have been resolved, as with the
exception of the CMC the consensus has trended towards the NCEP
suite with a weaker amplitude wave moving across Maine. This also
keeps the heaviest QPF further north into Northern New England.
The CMC is the lone outlier with a more amplified shortwave, and
is not preferred after 60 hours.

Previous Discussion:
There is very good model agreement through 60 hours with an
expansive ridge amplifying across the eastern half of the CONUS
and a trough in the Southwest. While the majority of this area
remains in good agreement with the evolution during D3, there are
discrepancies between the NCEP and Non-NCEP suite with a shortwave
moving across New England Monday night into Tuesday. The NCEP
members are generally weaker and further north with the energy
while the Non-NCEP is a bit more robust and further south. The
strength of the ridge across the Southeast as well as the speed of
the flow between this ridge and the closed lows in the Northwest
and near the Hudson Bay suggests a faster/weaker solution is more
likely. Although the latitudinal differences are pretty small, it
does impact the QPF footprint across the Northeast, and thus the
NCEP blend is preferred for D3 across the east.


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

Weiss