Prognostic Meteorological Discussion
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000
FXUS10 KWNH 251839
PMDHMD

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
238 PM EDT Fri May 25 2018

Valid May 25/1200 UTC thru May 29/0000 UTC

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

12Z model evaluation including final preferences and forecast
confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Subtropical Storm Alberto...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: NHC Track

The 12Z NAM and 12Z GFS start close to the consensus with the
surface system near the Yucatan Peninsula Fri afternoon, and
remain close to the consensus through Sun morning. After that
time, the 12Z NAM becomes faster than the consensus and further
west, as the ridging off the Southeast coast pushes it eastward.
The 12Z GFS has also shown a westward shift in its track, for the
same reasons as the 12z NAM. However, the 12Z GFS as also slowed a
bit, as the mid level reflection has slowed as well.

The 12Z UKMET continued its trends of being faster and further
east with the surface and mid level systems, as the mid level
ridging off the Southeast coast is not as far  east than the 12Z
GFS/CMC. The 12Z CMC has jogged eastward with the surface system,
due also to the mid level ridging off the Southeast coast moving a
bit further east. Finally, the 12z ECMWF slowed a bit and came in
a bit further east, as its mid level ridge over the Southeast was
a bit weaker and further east.


...Shortwave and surface wave clipping New England late Fri into
Mon...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend through 28/00z
            Non-12Z NAM blend after 28/00z
Confidence: Slightly above average

Both the 12Z NAM/GFS are close to the consensus as they take the
short wave energy over southern Manitoba Fri afternoon to a
position over western Quebec by Sun morning...as it weakens. The
frontal zone and surface wave weakens as they cross Quebec, and
the 12Z NAM/GFS are close to the consensus with this feature as
well.

After 28/00Z, the 12Z NAM becomes faster with the short wave
energy as it crosses northern New England. This appears to be due
to the influence of short wave energy in the fast mid level flow
over northern Ontario and northern Quebec, where the remainder of
the guidance is slower with this packet of short wave energy. As a
result, the 12Z NAM is faster with the surface wave that develops
on a frontal boundary southeast of Nantucket Island MA and tracks
well south of Nova Scotia. Because of this, the 12Z NAM is
excluded from the preference.


...Closed low central CA coast...crossing the Great Basin Sun into
Mon...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

Both the 12Z NAM/GFS are close to the consensus as they takes the
closed mid level low from the central CA coast Fri afternoon to a
position over NV/UT by 28/00z. After that time, the 12Z GFS
becomes a bit faster than the consensus, especially toward 29/00Z
(as does the 12Z UKMET). By contrast, the 12z ECMWF/CMC were
slower with the mid level system, but still within the consensus
envelope. At this point, with the timing differences occurring
late in the period, a general model blend is still preferred.

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

Hayes



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