Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1250 AM EDT Wed May 08 2019

Valid May 08/0000 UTC thru May 11/1200 UTC

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

00Z Model Evaluation with Preferences and Confidence
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...Upper trough crossing the Plains/Midwest/Great Lakes...
...Surface low advancing toward the Great Lakes...
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Preference: Non-NAM blend
Confidence: Above average

A southern stream closed low and associated trough axis over the
Four Corners region will eject progressively out across the
central/southern Plains early Wednesday before then quickly
lifting northeast toward the Midwest by Wednesday evening. On
Thursday, the height falls will cross the upper Great Lakes
region. This will drive low pressure initially over the central
High Plains that will lift northeast through the Great Lakes
through Thursday, with a trailing cold front that will cross the
central/southern Plains, lower/middle MS Valley and much of the
Eastern U.S. through Friday as the energy supporting shortwave
energy and surface low lifts up through southeast Canada. The
models all agree on this scenario, however, it should be noted
that the guidance strongly supports the southwest end of the front
slowing down and stalling out over the southeast TX coastal plain
and adjacent areas of the lower MS Valley on Friday and extending
into Saturday. The guidance overall is in rather good agreement
with the mass field evolution through the period, although the 00Z
NAM does gradually become a bit too slow it appears with its
frontal timing across the Eastern U.S. Will support a non-NAM
blend at this time.


...Series of shortwaves over the Northern U.S...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 00Z GFS/12Z UKMET/12Z ECMWF blend
Confidence: Slightly above average

A series of northern stream shortwaves will be traversing southern
Canada and portions of the northern Plains, the upper Midwest, and
 the Great Lakes region through the period. Model spread is modest
through most of the period, but the 00Z NAM and 12Z CMC are both a
bit stronger than the 00Z GFS, 12Z UKMET and 12Z ECMWF by the end
of the period with a rather vigorous shortwave trough and
associated low center dropping down toward the upper Midwest. The
GFS, UKMET and ECMWF have better overall ensemble support, so a
blend of these solutions will be preferred.

 
...Trough digging into the Intermountain West...
...Closed low evolution over the Southwest U.S....
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Preference: General model blend 
Confidence: Above Average 
 
The models agree in digging a northern stream shortwave down from
southwest Canada and into the Intermountain West through
Wednesday. Some of this energy will then eject east out across the
Plains, but there will be a portion of it that breaks away and 
retrogrades down to the southwest and interacts with a new
southern stream closed low feature approaching the Baja Peninsula
by Thursday. This will lead to an elongated trough over much of
the Southwest U.S. with a rather broad closed low feature over CA
and adjacent areas of the Southwest U.S. by the end of the period.
The guidance is reasonably well clustered at this point, so a
general model blend will be preferred.


...Shortwave/frontal interaction over southeast TX...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-NAM blend
Confidence: Slightly above average

Southern stream shortwave energy lifting northeast out of
northeast Mexico and across the lower Rio Grande Valley late
Thursday through Friday and into early Saturday will be
interacting with a frontal zone stalling out over the southeast TX
coastal plain or perhaps near the middle and upper TX coast. The
00Z NAM is a bit more out of tolerance with the global models with
this energy, and so a non-NAM blend will be preferred. It should
be noted that this set-up over southeast TX is expected to favor
multiple rounds of heavy to excessive rainfall, leading to
potentially high-impact flash flooding. Please consult the latest
WPC QPFERD for more details concerning this.

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

Orrison