Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1233 PM EDT Sat May 26 2018

Valid May 26/1200 UTC thru May 30/0000 UTC

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

12Z model evaluation including initial preferences and confidence
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***Subtropical Storm Alberto***
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Preference: See NHC Forecast
Closest Guidance: 00z ECMWF/CMC blend

The initial setup and placement of low center development
continues to remain key on timing and the track across the eastern
Gulf of Mexico this weekend.  The 00Z UKMET is initially the
slowest with the storm through early Sunday and then becomes the
eastern most solution by Sunday night and into early Monday as it
approaches the central Gulf Coast.  The 00Z CMC is also on the
slower side initially, but not to the same degree as the UKMET.
There is good overall agreement among the NAM, GFS, and ECMWF
through midday Sunday, after which the ECMWF is slower with the
storm making landfall Monday night.  The official NHC forecast has
more details on Subtropical Storm Alberto.


***Disturbances crossing the Great Lakes and Northeast U.S.***
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Preference: General model blend
Confidence: Above average

Elongated shortwave energy along the US/Canadian border into the
Great Lakes will shift through the low amplitude but solid ridging
across the northern Great Lakes into northern New England late
Saturday into Sunday.   The tail frontal zone of the preceding
system will be draped along 40N.   The weak height falls will
support weak cyclogenesis along the boundary south of Long Island
Monday.  There is strong agreement in the latitude of the
track/frontal orientation, but the timing of the wave differs,
driven mainly by the weakness of the energy getting through the
block as well as rotating from the south. 

Compact shortwave from the Gulf of Alaska lifts over the longwave
ridge in western Canada toward Hudson Bay by early Monday.  Here,
general troughing/weakness allows for sharpening/southward
amplification with strong jet enhancement along the base in Quebec
by early Tuesday.  This supports a strong surface low with
trailing cold front to press through northern New England at the
end of the forecast period.   For such a fast moving wave in the
larger scale pattern, the system is fairly well agreed upon. 
Confidence is slightly above average given fairly good agreement
in typically more random environment/setup, suggesting modest
predictability at this range in time.


***Western U.S. closed low and surface cold front***
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Preference: General model blend
Confidence: Above average

Models continue to be strongly agreed upon with the evolution of
the closed low through the Great Basin Sunday into Monday.  Even
as the upper low begins to break down and lift northeastward into
the northern and north central Rockies Monday, the timing/shape
and evolution of the wave are fairly well agreed upon including
the interaction with northern stream connection across Montana
into late Monday/Tuesday.  WPC will continue to support a general
model blend at above average confidence (though reducing slightly
due to mesoscale/convective influences toward Tuesday).


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

Hamrick/Gallina