Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
251 AM EDT Fri May 18 2018

Valid May 18/0000 UTC thru May 21/1200 UTC

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

00Z model evaluation...with preferences and confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Broad upper trough and embedded MCVs over the Southeast...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
Preference: General model blend
Confidence: Above average

The latest guidance has come into rather good agreement now with
the gradual ejection of the large scale trough out of the
southeast CONUS going through this weekend. A general model blend
will be preferred.


...Upper trough crossing the upper Midwest this weekend...
...Cold front/surface wave crossing the region...
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Preference: Non-NAM blend
Confidence: Above average

The 00Z NAM again stands out as being a somewhat slower and deeper
outlier solution with this system compared to the otherwise well
clustered global model and ensemble guidance. Will prefer a
non-NAM blend.


...Large upper trough/closed lows over the West...
...Ejecting east across the central Plains this weekend...
...Crossing the Midwest by Monday...
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Preference: Blend of the 00Z UKMET, 00Z CMC and 00Z ECMWF
Confidence: Below average

Multi-model trends with this system over the last 24 hours
continue to be generally slower and deeper as a large portion of
the Western U.S. trough axis and associated closed low energy
ejects out across the Plains this weekend. There is significant
disagreement between the NCEP and non-NCEP guidance on the details
of the energy as it crosses the central Rockies Saturday and edges
out into the central Plains on Sunday. The 00Z NAM and 00Z GFS
become both stronger and slower than the 00Z UKMET, 00Z CMC and
00Z ECMWF. Despite the slower overall trend in the guidance, there
are concerns with both the NAM and much more so the GFS as a
result of convective feedback. This feedback is likely resulting
in an unrealistically slow and deep solution. The non-NCEP models
however could still be a little too fast, and especially the ECMWF
at this point as the UKMET and CMC are both slower than the ECMWF.
The 00Z GEFS mean though is seen as still being a bit more
progressive than the NAM/GFS camp, and thus the preference will
still be to stray away from the NAM and GFS overall. With a
notably below average degree of confidence, the preference will be
to favor a non-NCEP blend involving the UKMET, CMC and ECMWF.


...Upper trough digging into the West on Sunday...
...Energy lifting north out of the northern Rockies...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

Overall trends in the models have moved toward a deeper trough
axis across the West Coast by Sunday morning, with all of the
models supporting a closed low dropping down through CA by Monday.
These height falls will be responsible for kicking the lingering
energy over the northern Rockies region up to the north and into
southwest Canada. Model spread with that system is fairly minimal
with the complete 00Z cycle of guidance, and thus a general model
blend will be preferred at this point.


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

Orrison