Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1255 PM EDT Sun May 27 2018

Valid May 27/1200 UTC thru May 31/0000 UTC

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

12Z model evaluation including preliminary preferences and
confidence
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...Subtropical Storm Alberto...
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Preference: See NHC Forecast

As Alberto moves through the northeast Gulf toward the coast, the
models remain fairly well clustered, with the NAM/GFS remaining on
the western edge of the guidance and the 00Z EC more closely
aligned to the latest official NHC track.  After coming onshore,
the 12Z GFS begins to lag behind the NAM and 00Z ECMWF (which
remain fairly well-clustered through late Wed) as Alberto moves
north through the Tennessee and Ohio valleys toward the upper
Great Lakes region.  The 00Z UKMET remains on the eastern edge of
the deterministic guidance through much of the period and the 00Z
Canadian is a slower outlier once the system moves onshore.  Refer
to NHC outlooks for the latest preferred track guidance.

...Approaching northern stream shortwave and frontal zone across
northern Great Lakes into New England Mon to Tues...
...Developing surface low southeast of Long Island by early Mon...
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Preference: General model blend
Confidence: Above average

Overall through 12z Mon as the developing surface low begins to
move well offshore, the deterministic models are in good agreement
with the larger scale features.


...Western U.S. closed low lifting into the northern Plains by
Wed...associated lee cyclones/trof with eventual consolidation
across MT/ND by Wed...
...Shortwave ejecting east across the central Plains into the mid
Mississippi valley...
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Preference: General model blend until 29/12z
            Non-GFS/NAM thereafter
Confidence: Average

While differences in the details remain, models remain in
generally good agreement with the larger-scale features through
early Tue.  As noted in the overnight runs, the GFS moves to the
southern/slower edge of the guidance with the core of the upper
low/surface reflection as it moves out into the Dakotas late Tue
into Wed.  The NAM and 00Z non-NCEP deterministic guidance are a
little better clustered here.  The NAM is more of an outlier
further south with a shortwave pivoting east through the base of
the trough through the central Rockies into the central Plains Tue
night.  While most of the deterministic guidance offers some
indication of this wave, the NAM maintains a more amplified
shortwave longer into the period from the central Plains into the
mid-Mississippi valley than the other deterministic models. 


...Longwave trof amplifying south into Pacific Northwest by Wed...
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Preference: General model blend
Confidence: Average

There are still some differences with respect to the timing of the
trailing subtropical stream portion of the trough extending from
the northern California back into the eastern Pacific on Wed, but
overall the deterministic models are fairly well-clustered through
the end of the period.

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

Pereira