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Model Diagnostics Discussion
(Caution: Version displayed is not the latest version. - Issued 0416Z May 21, 2018)
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Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1216 AM EDT Mon May 21 2018

Valid May 21/0000 UTC thru May 24/1200 UTC

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

00Z model evaluation...with preferences and confidence

...Weakening shortwave energy over the Midwest...
...Surface wave crossing the OH Valley/Lower Great Lakes...
Preference: Non-NAM blend
Confidence: Above average

There is good model agreement in general with the shortwave energy
currently moving across the Midwest which will move downstream and
gradually shear out across the OH Valley through Tuesday. The
energy though will be strong enough to foster a wave of low
pressure across the OH valley and lower Great lakes region through
Tuesday which will move into the Northeast Tuesday night. The 00Z
NAM is perhaps a little too strong with the energy as it moves
downstream. The global models are rather well clustered surface
and aloft, so will suggest a non-NAM blend at this time.

...Trough digging across the Northeast by Tuesday/Wednesday...
Preference: Non-NAM blend
Confidence: Above average

The guidance depicts an amplification of a northern stream
shortwave trough across the Northeast by Tuesday and Wednesday.
The 00Z NAM edges toward the stronger side of the model suite,
with the global models all a little less amplified. Will prefer a
non-NAM blend with this evolution for now.

...Large scale trough/closed low impacting the West...
...Energy crossing the northern High Plains by Thursday...
Preference: Blend of the 00Z GFS, 12Z UKMET, and 12Z ECMWF
Confidence: Average

The models are in excellent agreement in digging height falls
across the West over the next couple of days which includes a
well-defined closed low that digs in across the Southwest through
Tuesday. 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 00Z NAM in general looks a little too
deep with the troughing across the Intermountain West, and the 12Z
CMC is the most progressive by the end of the period to eject its
height falls out across the High Plains. The 00Z GFS, 12Z UKMET
and 12Z ECMWF are well clustered with their respective timing and
depth details, and given good ensemble support, a blend of these
solutions 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
Preference: Blend of the 12Z UKMET and 12Z CMC
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, but the guidance is rather well clustered
on at least a very well-defined and convectively enhanced vort
that will cross over southeast NM and far west TX early Tuesday
before lifting up across the High Plains. Generally speaking, the
00Z NAM and 00Z GFS look a bit too amplified, and the GFS
definitely has some convective feedback concerns at least briefly
over southeast NM and west TX. The 12Z ECMWF though does not look
strong enough which is also reflected in its QPF fields. A
compromise toward the 12Z UKMET and 12Z CMC will be preferred
which supports a solution in between stronger and weaker camps.

Model trends at
500 mb forecasts at