Prognostic Meteorological Discussion
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000
FXUS10 KWNH 260637
PMDHMD

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
236 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 model evaluation including final 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: General model blend
Confidence: Slightly above average

The 00Z UKMET/CMC trended more west with the track of a surface
low as it moves through the Mid-Atlantic region early Friday, and
are now closer to the previous preference of the NAM/GFS/ECMWF.
The 00Z ECMWF nudged slightly in the direction of the 00Z NAM/GFS
but minor differences remain.

Regarding the phasing energy over the Great Lakes/Northeast for
the weekend, there continues to be convergence with subsequent
model cycles as seen with the previously faster 12Z ECMWF having
adjusted slower with its 00z run toward the 00Z NAM/GFS.
Similarly, the 00Z UKMET and CMC now look closer to the previous
preference, such that a general model blend can be used for this
system.


...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. No significant differences were noted with the 00Z
ECMWF/UKMET/CMC relative to their 12Z cycles.


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

Good agreement exists with this system until late Saturday, when
the 00Z 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 00Z ECMWF/12Z ECMWF mean a bit
slower. Ensemble spread is modest for the day 3 time frame, but it
appears a blend of the 00Z NAM/GFS/ECMWF is closest to the middle
of the ensemble spaghetti plots, versus the farther south 00Z
UKMET/CMC.


...Weak southern stream shortwave ejecting out toward the southern
High Plains by Saturday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 00Z NAM, 00Z GFS and 00Z 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 00Z
CMC and especially the 00Z 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, but
the 00Z UKMET did trend a bit weaker, while continuing to lie on
the stronger edge of the available ensemble guidance. The 00Z NAM,
00Z GFS and 00Z 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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