Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1234 PM EDT Tue May 21 2019

Valid May 21/1200 UTC thru May 25/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence...
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...Deep layer low/trough over the Central U.S...
...Reaching the Northeast on Friday...
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Preference: General model blend...through 00Z/24
            12Z NAM/12Z GFS/00Z ECMWF blend...after 00Z/24
Confidence: Above average

The 12Z models (NAM and GFS in this case) are in better agreement
compared to the 00Z/06Z cycles and support the deep layer closed
low over the central U.S. lifting off to the northeast through the
upper Midwest and Great Lakes region through Wednesday and
Thursday. The energy though is expected to then advance east and
southeast down across the Northeast on Friday as the entire system
rounds the top of a strong subtropical ridge developing over the
Gulf Coast states and Southeast through the period. The 00Z UKMET
reflected stronger height falls and a closed low feature impacting
New England on Friday compared to the remaining guidance, but the
00Z CMC was the weakest and also a tad more progressive versus the
model consensus. Sufficient mass field agreement exist for a
general model blend to be preferred at this point which will help
resolve some of the smaller scale differences with depth and
timing. The 12Z NAM/GFS and 00Z ECMWF solutions are well
clustered. Will prefer a general model blend through 60 hours as
this system approaches and crosses the Great Lakes region, but
then will lean toward a blend of the NAM/GFS and ECMWF thereafter.


...Vigorous Pacific closed low digging into the West...
...Lifting across the Northern Plains by Friday...
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Preference: General model blend
Confidence: Above average

There is good agreement with the next deep layer closed low that
drops down across the West through Thursday and then lifts
northeast across the northern Plains on Friday. The 00Z ECMWF may
be a tad too strong with its height falls crossing the northern
Plains on Friday, but for the time being a general model blend
should suffice with this mass field evolution.


...Closed low/trough over the Pacific Northwest on Friday...
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Preference: General model blend
Confidence: Above average

All of the models agree in dropping yet another upper trough and
associated closed low down into the Pacific Northwest on Friday.
The 12Z NAM/GFS and 00Z ECMWF are just a tad stronger than the 00Z
UKMET/CMC solutions, all of the guidance is well within the
ensemble model spread, and so a general model blend will be
preferred.


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

Orrison