Prognostic Meteorological Discussion
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FXUS10 KWNH 270432

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1231 AM EDT Fri Apr 27 2018

Valid Apr 27/0000 UTC thru Apr 30/1200 UTC

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

00Z NAM/GFS evaluation...with preliminary preferences

...Evolution of the eastern CONUS trough through Sunday...
...Shortwave pushing through the Southeast today, phasing with
digging wave into the Great Lakes and Northeast by Saturday...
...Weak East Coast surface low development Friday-Saturday...
Preference: 00Z GFS, 12Z ECMWF blend
Confidence: Average

Minor detail differences exist with this system, but the 00Z NAM
ends up toward the slower side with a related cold front moving
through the central and northern Appalachians Saturday. Toward the
end of the period...12Z/30, the 12Z UKMET/CMC appear to be too
fast/east with the mid-level closed low over the Northeast with
better ensemble support existing near the 00Z GFS and 12Z ECMWF.

...Positively tilted shortwave over the southern Plains, digging
toward Florida tonight...
Preference: General model blend
Confidence: Average

The models show similarly with this system.

...Closed low reaching the West Coast today, opening into a trough
over the Northwest by Monday...
Preference: 00Z NAM, 00Z GFS, 12Z ECMWF blend
Confidence: Average

The latest ensemble spaghetti height plots show the 12Z UKMET and
12Z CMC differ from the better clustering represented well in the
ensemble means. While the 00Z GFS and 12Z ECMWF show the best
agreement to the ensemble means, cannot rule out the 00Z NAM as
part of a blend, given detail differences in individual vorticity
maxima as the closed low begins to open up heading into Monday.

...Weak southern stream shortwave ejecting out toward the southern
High Plains by Saturday...
Preference: 00Z NAM, 00Z GFS, 12Z ECMWF blend
Confidence: Slightly above average

The 12Z UKMET/CMC continue to stand out as stronger outliers
regarding mid-level heights crossing into Texas on Saturday.
Strong ensemble support exists for a non-12Z UKMET/CMC blend best
represented by the 00Z NAM, 00Z GFS and 12Z ECMWF.

Model trends at
500 mb forecasts at


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