Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
357 PM EDT Sat Apr 20 2019

Valid Apr 20/1200 UTC thru Apr 24/0000 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: General model blend
Confidence: Average

On the synoptic scale, there is generally good model agreement
across the CONUS. Across the eastern U.S., the closed upper level
low will continue to move northeast, reaching New England by the
end of the forecast period. Through 48 hours, the guidance is in
good shape with very little differences noted in the mass fields.
On Day 3, the 12z NAM takes the ULL a bit further to the NW
compared to the rest of the guidance, but is still within the
model spread. It also is much quicker to kick out of the region by
the end of Day 3, so something to consider and investigate further
with the rest of the 12z guidance coming in. With its further NW
ULL, the developing surface low expected offshore also takes a NW
shift compared to the other models, which are in rather good
agreement. The UKMET is somewhat similar to the NAM, while the
ECMWF/CMC/GFS are in very good agreement and show very similar
solutions. For this system, a general model blend through 48 hours
is preferred, then a non-NAM blend is preferred.

Across the rest of the CONUS, a closed upper level low is expected
to track across the southern US and Four Corners region. Here
model agreement across the board is very good so a general model
blend is more than sufficient and the NAM can be included through
the whole forecast period as well, despite some QPF differences
developing across the southern/central Plains due to convective
issues.

A shortwave trough moving through the Great Basin and northern
Rockies will push into the northern Plains and lead to surface
cyclogenesis by Day 3 across the Upper Midwest. There is fairly
good model agreement in the mass fields and QPF with this system
through the period such that a general model blend is preferred
here as well.

Overall, despite some minor differences across the CONUS, a
general model blend is preferred with less inclusion to the NAM on
day 3 across the east.


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

Taylor