Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1215 PM EDT Sun Apr 28 2019

Valid Apr 28/1200 UTC thru May 02/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: Non-NAM blend
 Exceptions: Lower % GFS in blend after 30/00z
             Remove 00z CMC from blend after 01/12z
Confidence: Slightly above average through 30/00z
            Average to slightly above average afterward


A system exiting New England today looks to have come into solid
agreement and sets up a fairly equal starting point any lingering
energy/frontal zone across the Mississippi and Ohio River Valleys
for the next approaching systems.

The northern stream wave currently over the High Northern Plains
of MT is already well mature and compact and will be sliding
southwest into the Dakotas later today before shearing toward the
NNE in the Boundary Waters of MN by late Monday, with typical
minor model variance; ie, the NAM a bit stronger/slower to wind
down and the CMC being a bit slower in timing and therefore a bit
stronger as well.  However, the southern portion of the shortwave
height-falls across the Dakotas into the mid-MO river valley will
be intersecting with strong return flow from the Western Gulf and
spark a weak surface wave out of the CO Lee low and active
convection across KS that will track toward IL by Monday. Here the
NAM's stronger solution appears to draw the QPF/forcing axis
northward relative to the other guidance, enough to suggest a
Non-NAM or a very low NAM weighting in the general model
blend...including across New England on Tuesday, as it shears into
zonal flow.

Lingering northern stream trough energy across the Northern
Rockies and points westward Monday/Tuesday will begin to amplify,
the resulting southwesterly flow will direct the closed low
currently well southwest of S CA, through the Four Corners region
by Tuesday morning, shearing into the confluent southwesterly flow
.  This will set up another surface wave along the frontal zone
out of SE CO across the Central Plains toward N IL Tuesday into
Wed.  The 00z ECMWF trended faster and has lined up with earlier
cycle preferences of the 00z UKMET/CMC.  The 12z NAM continues to
hold steadfast toward a faster ejection of the southern stream
wave through the Plains but lost its timing partner, as the 12z
GFS depicted a sizable slowing of the wave.  The 12z GFS is still
in line with typical bias toward weakening faster than the
ECMWF/CMC/UKMET which will reduce southward convective growth
(increased capping) of convective complex, the timing is good to
have some increased inclusion of the guidance to the blend.  In
fact, the 00z CMC is a bit faster and weaker than the UKMET/ECMWF
and more more middle ground to the GFS, to suggest a lower
weighting compromise with the GFS.   As such will suggest a
ECMWF/UKMET/CMC blend with some lower GFS weighting, but with
still modest spread confidence is increasing but only average to
slightly above average overall.

As the southern stream lifts through, the digging northern trof
through the Intermountain West swings through into the Central
Plains by 00z Thurs.  Here the 00z CMC appears to deepen and stall
relative to the ejection of the UKMET/GFS and ECMWF...so will
support removing the CMC through the Central Rockies after 01/12z
Wed. 


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

Gallina