Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1237 AM EDT Sat Apr 20 2019

Valid Apr 20/0000 UTC thru Apr 23/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: 00Z GFS, 12Z ECMWF, 12Z CMC
Confidence: Average

Deterministic models are generally in good agreement with their
mass fields and the overall synoptic pattern across the CONUS over
the next several days. For the height fields aloft, the ECMWF,
GFS, and CMC are all relatively close to the ensemble means and
well within the envelope of ensemble spread. The exception would
be the 12Z UKMET, particularly as it relates to the trough pushing
into the West. The UKMET is out of phase with every single
deterministic model and ensemble member (NAEFS+ECMWF). It closes
off a mid-level low about 600km west of the other models. For this
reason the UKMET is excluded from the preference.

Otherwise, models are reasonably similar. The greatest remaining
differences occur in two main areas. First, the NAM generally
places the axis of QPF further south over the Great Lakes on Day 3
(Monday and Monday Night), and this is likely due to slightly more
amplification to the broad trough near the Canadian border. This
is a typical bias in the NAM, so the preference is to lean away
from the NAM in that respect. Second, another low is forecast to
develop off the coastal Carolinas and then move toward the New
England coast as the closed low begins to eject east toward the
Atlantic. There are differences in strength and placement with
this low; the CMC and ECMWF are stronger and closer to the coast,
while the NAM and GFS are weaker and further offshore. This does
lead to considerable QPF differences. The preference is for a
blend at this point; there are not many ensemble members as strong
as the deterministic ECMWF and CMC.


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

Lamers