Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
110 PM EDT Thu May 17 2018

Valid May 17/1200 UTC thru May 21/0000 UTC

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

12Z NAM/GFS evaluation...with preliminary preferences
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...Upper troughing/cold front crossing the Northeast
today/Friday...
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Preference: General model blend 
Confidence: Above average 

The models show similarly with this system.


...Broad upper trough over the Southeast third of the CONUS...
...Upstream MCVs digging into the Southeast U.S. trough...
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Preference: near the 00Z ECMWF
Confidence: Slightly above average

The 12Z NAM/GFS are quicker to move the base of the trough axis
toward the east for Saturday/Saturday night, but with a blocking
ridge to the east and biases in the GFS to be too quick to slide
upper trough axes to the east, it seems more reasonable to stay
toward the slower side of the guidance. The 00Z ECMWF may have
room to speed up a bit, but ensemble data is weighted near the 00Z
ECMWF at this time, with the 00Z UKMET a bit slower and 00Z CMC
quicker/flatter.


...Large upper trough/closed lows over the West...
...Ejecting east across the central Plains this weekend...
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Preference: 12Z GFS / 00Z ECMWF blend
Confidence: Below average

Ensemble and deterministic trends have been stronger with a closed
low forming over the central High Plains Friday night as a large
western trough moves east. While this is likely a result of
convective enhancement, the stronger 12Z NAM/GFS may be showing
some elements of feedback, but the 00Z UKMET is on the weaker side
of the latest deterministic guidance.

Regarding the surface evolution, the ensemble scatter low plots
show a large degree of spread with the GEFS members clustered more
to the west and ECMWF members farther east. Toward the middle of
this spread is what will be preferred at this time but with
reduced confidence.


...Upper trough crossing the upper Midwest this weekend...
...Cold front/surface wave crossing the region...
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Preference: Non 12Z NAM blend
Confidence: Slightly above average

The 12Z NAM stands out in the ensemble guidance as a near outlier
with a slower/deeper trough axis over the northern Plains. Outside
of the 12Z NAM, the models show reasonable agreement.


...Upper trough digging into the West on Sunday...
...Energy lifting north out of the northern Rockies...
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Preference: non 00Z ECMWF blend
Confidence: Average

While the 00Z CMC may lie toward the stronger side of the model
guidance, overall trends in the models have moved toward a deeper
trough axis. The 00Z ECMWF stands out as weakest, so it will be
discounted at this time. Ensemble spaghetti plots, including the
00Z ECMWF mean, show broad support for a non 00Z ECMWF blend.


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

Otto