Prognostic Meteorological Discussion
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FXUS10 KWNH 220420
PMDHMD

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1220 AM EDT Tue May 22 2018

Valid May 22/0000 UTC thru May 25/1200 UTC

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

00Z model evaluation...including preferences and confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Trough digging across the Northeast by Tuesday/Wednesday...
...Surface low crossing the OH Valley and Northeast...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The guidance generally depicts an amplification of a northern
stream shortwave trough across the Northeast through Tuesday and
Wednesday as a surface wave ejects across the OH Valley and
interior of the Northeast. There is good agreement seen out of the
models and so a general model blend will be preferred.


...Large scale trough/closed low impacting the West...
...Energy crossing the northern High Plains by Thursday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Average

The models are in excellent agreement in digging height falls
across the West through Tuesday which includes a well-defined
closed low that digs in across the Southwest. On Wednesday, this
closed low feature will begin to lift off to the northeast, and
the energy should open up into a progressive trough by Thursday
that will be ejecting up across the northern High Plains. The
guidance is reasonably well clustered at this point, and so a
general model blend will be preferred.


...Mid level trough/closed low lifting up across the Southeast...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The guidance is in very good mass field agreement with this
system, so a general model blend will be preferred.


...Shortwave energy/vorts lifting across the Plains Tuesday and
Wednesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Average

Multiple shortwave impulses are expected to lift northeast out of
the base of the Western U.S. trough and across the Plains on
Tuesday and Wednesday, and there appears to be better model
clustering at this point with the overall details. The 00Z GFS
does exhibit a little bit of convective feedback from the outset
over southeast NM with its ejecting energy, but then quickly comes
into alignment with the remaining models across the Plains through
the period. Will prefer a general model blend as a result.


...Upper trough/closed low offshore the West Coast by Wednesday
and Thursday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-UKMET blend
Confidence: Slightly above average

The models drop another upper trough and associated closed low
feature south down off the West Coast by Wednesday and Thursday.
The 12Z UKMET is a bit weaker than the remaining models with its
closed low offshore CA by the end of the period and is also a bit
farther south. The remaining guidance is rather well clustered on
a bit stronger solution that is a little farther north. Will
suggest a non-UKMET blend at this point.


...Surface low development over the Gulf of Mexico by Friday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 12Z ECMWF
Confidence: Average

The latest deterministic guidance and ensemble plots generally
favor the idea of a relatively broad low to mid level low center
evolving north of Yucatan Peninsula by Friday that will be lifting
north toward the central Gulf of Mexico. The 00Z NAM is by far the
faster solution with this, with the 12Z ECMWF and 12Z CMC slower
and farther south as a result. The 00Z GFS and 12Z UKMET however
show little in the way of a surface low feature this period. The
latest ensemble data is rather strongly in favor of a developing
low led especially by the European and Canadian ensemble members,
but also including a number of GEFS members which suggest the GFS
and UKMET are too benign with their evolution of this system. The
CMC though looks generally too strong at this point. The
preference will be toward the 12Z ECMWF given its good ensemble
support.


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

Orrison

$$





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