Prognostic Meteorological Discussion
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000
FXUS10 KWNH 260439
PMDHMD

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1239 AM EDT Thu Apr 26 2018

Valid Apr 26/0000 UTC thru Apr 29/1200 UTC

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

00Z NAM/GFS evaluation including preliminary preferences
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Mid-level shortwave lifting north along the New England coast
today, interacting with a northern stream shortwave crossing the
Great Lakes...
...Surface low departing from the Northeast today/tonight...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The models show similarly with this system.


...Mid-level energy departing from the lower MS valley this
morning and crossing the Southeast by Friday...
...Low pressure lifting from the Southeast to the Northeast Friday
and Saturday...
...Phasing with northern stream energy over the Northeast by
Saturday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 00Z NAM, 00Z GFS and 12Z ECMWF
Confidence: Slightly above average

The 12Z UKMET/CMC are a displaced off to the east relative to the
better ensemble clustering regarding the surface low as it tracks
through the Mid-Atlantic region early Friday. The 00Z NAM, 00Z GFS
and 12Z ECMWF show better agreement to the ensemble low plots and
the ensemble means.

Regarding the phasing energy over the Great Lakes/Northeast for
the weekend, there are some timing differences to speak of with
the 12Z ECMWF a bit faster than the 00Z GFS, with the 00Z NAM in
the middle. The 500 mb pattern shown by the 12Z UKMET is less
amplified than the remaining consensus, so the 12Z UKMET is
excluded here as well, despite its surface low looking to be in a
reasonable spot.


...Positively tilted upper level shortwave crossing the upper MS
valley and central Plains today, with the southern portion of the
trough reaching the eastern Gulf Coast Friday night...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Slightly above average

The models only show minor placement differences, with a blended
approach yielding a solution near a blend of the ensemble means.
Given differences are small, a general model blend can be used for
this system.


...Closed low evolution toward the West Coast by Friday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 00Z NAM, 00Z GFS, 12Z ECMWF blend
Confidence: Average

Good agreement exists with this system until late Saturday, when
the 12Z UKMET/CMC depict a sharper mid-level trough axis over the
West, while also being displaced toward the southern side of the
deterministic spread. The 00Z GFS is a bit faster to move the
upper trough to the east, while the 12Z ECMWF is a bit slower. The
12Z ECMWF mean is between the faster and slower camps, and appears
to be a decent fit at this time, along with the 00Z NAM, given
typical biases in the GFS and ECMWF to be fast and slow,
respectively.


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

The models eject a weak southern stream shortwave out of the
Southwest and toward the southern High Plains by Saturday. The 12Z
CMC and especially the 12Z UKMET are a bit stronger and better
defined with the energy as it ejects out across eastern NM and
western TX. The 12Z UKMET is a near outlier with respect to the
latest ensemble spaghetti heights at 500 mb Friday evening. The
00Z NAM, 00Z GFS and 12Z ECMWF are all a bit weaker and sheared in
their appearance, and fit better into the ensemble clustering.


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

Otto

$$





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