Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
414 PM EDT Sat Apr 13 2019

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

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

12Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: Blend of 12Z GFS, 12Z ECMWF, 12Z CMC
Confidence: Slightly above average

---19Z UPDATE---
No change to the preliminary preference. A blend of the GFS, ECMWF
and CMC still seems to provide a reasonable forecast.

---PREVIOUS DISCUSSION---
The greatest source of model spread over the next few days over
the CONUS is disagreements over the strength and amplitude of the
trough that will be ejecting into the Eastern U.S. by Monday. The
12Z NAM shows substantially lower heights at the core of the
trough as it moves through the Great Lakes and Ohio Valley,
indicative of a stronger trough on that model. This also yields
some colder temperature profiles in the region, and the NAM is
excluded from the preference despite a surface low track that is
reasonably similar to the global models.

Otherwise, the global models are in fairly good agreement. The 00Z
UKMET does deamplify the trough a bit faster than the other
models, so less weight was placed on that model for the eastern
half of the country. A blend of the ECMWF, GFS and CMC produces a
reasonable consensus forecast in these areas.

Behind the initial trough -- in the Central and Western U.S. --
the NAM and the UKMET continue to be the models that deviate most
strongly from ensemble means and the other global deterministic
models. The UKMET is stronger and slower with a trough approaching
the West Coast on Monday, with a greater amplitude to the
downstream ridge. The NAM, meanwhile, has a strong trough on the
West Coast but it is faster than the other models, and has lower
heights downstream across much of the central U.S. Therefore, a
blend of the GFS, ECMWF and CMC is preferred given more
substantial ensemble support.


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

Lamers