Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1232 AM EDT Sat Apr 06 2019

Valid Apr 06/0000 UTC thru Apr 09/1200 UTC

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

00Z NAM/GFS Model Evaluation with Initial Preferences and
Confidence
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...Overall Pattern Across the CONUS...
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Preference: Blend of 00Z GFS and 12Z ECMWF
Confidence: Average

A broadly zonal flow pattern continues across the CONUS over the
next several days with most shortwave interaction within the
northern or southern stream as opposed to complete phasing of the
northern and southern streams. The areas of main concern are with
northern stream shortwave arrival timing into the Pacific NW
Saturday, the northern stream shortwave crossing the Great Lakes
Sunday night and its associated effects into the Northeast Monday,
and the southern stream shortwave trough development and
progression northeast from TX starting Sunday.

Amplitude of the shortwaves as they progress east across the CONUS
seems to be the largest difference maker among global guidance.
The 00Z GFS became more meridional in the northern stream on Days
2/3 which brought it in good general agreement with the 00Z ECMWF.
QPF is similar between the 00Z GFS and ECMWF with the most notable
exceptions in the northeast; on Day 2 the GFS more progressive
near the New England Coast and on Day 3 the GFS is farther south
with the QPF axis over Maine. The GFS is often too progressive and
the ECMWF too slow, so a compromise on Day 2 is warranted. This
northern stream change in the 00Z GFS also allows the southern
stream trough to slow and become more in line with the 12Z ECMWF
with a similar QPF axis.

Differences appear in the shortwave pattern with the 00Z NAM and
12Z UKMET/CMC which are great enough to allow the focus to be on
the GFS/ECMWF for now. The 00Z UKMET is the most meridional and
amplified solution while the 12Z CMC and 00Z NAM are more zonal
with the northern stream.


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

Jackson