Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1246 AM EDT Mon Apr 02 2018

Valid Apr 02/0000 UTC thru Apr 05/1200 UTC

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

00Z Model Evaluation...Including Model Preferences and Confidence
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...Shortwave exiting the Mid Atlantic with a weak surface low also
quickly moving out into the Atlantic...
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Preference: General model blend
Confidence: Above average

Models are in good agreement for this system, which will mostly
provide impacts in the CONUS over the next 12-18 hours before
moving out into the Atlantic. Therefore, a general model blend is
preferred.


...Upper level trough over the Northwest today continuing to dig
to the Upper Midwest by Tuesday...
...Surface cyclogenesis over the Plains today with a deepening low
moving into the Great Lakes Tuesday...
...Low lifting into Quebec with trailing cold front clearing the
East Coast through Wednesday...
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Preference: 00Z GFS; 12Z ECMWF Ensemble Mean
Confidence: Average

There continues to be a convergence of model forecasts for this
system, with reduced spread over the past several model cycles.
Many models and ensemble members are showing a similar trajectory
of the surface low track, but there are still some differences on
timing. The 12Z ECMWF continues to represent the slower end of
model spread, particularly during the day on Tuesday before the
surface low begins to occlude and timing differences are somewhat
reduced. The 12Z UKMET and CMC are on the faster end, with the 00Z
GFS, 18Z GEFS Mean, and 00Z ECMWF Ensemble situated in the middle.
The 12Z NAM has a surface low track a little further south than
the consensus, and is not preferred for this reason.

The preference will maintain continuity with the past several WPC
evaluations, with the 00Z GFS offering an intermediate timing that
is also very close to the ECMWF Ensemble Mean and a significant
cluster of ensemble members.


...Low-amplitude shortwaves approaching the Pacific Northwest by
Tuesday Night and Wednesday Morning...
...Surface wave approaching Vancouver Island by late Wednesday...
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Preference: 18Z GEFS Mean; 12Z ECMWF Ensemble Mean
Confidence: Below Average

Limited confidence continues for the series of shortwaves that
will push toward the Pacific Northwest by mid-week. Models
generally all agree that some initial low-amplitude shortwaves
will arrive first on Wednesday, but are in some cases completely
out of phase with the individual waves. There is also general
agreement that a more amplified shortwave may reach 140W by
Wednesday Night, with an associated surface low. Confidence is
lower in the details, as there is a considerable amount of
variability in the operational models. The preference is to
continue to lean toward the ensemble means, of which the GEFS Mean
and ECMWF Ensemble Mean capture the general ideas offered by the
operational models, and are actually reasonably close in their
height fields aloft.


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

Lamers