Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
101 AM EDT Thu May 02 2019

Valid May 02/0000 UTC thru May 05/1200 UTC

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

00Z Model Evaluation with Preferences and Confidence
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...Southern stream trough/wave activity over the South...
...Energy lifting northeast across the OH/TN Valleys...
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Preference: 00Z GFS/12Z ECMWF and 12Z ECENS mean blend
Confidence: Average

A series of southern stream shortwave impulses will continue to
lift northeast from the southern Plains up across the OH/TN
Valleys and into the Mid-Atlantic region going into the weekend.
This will allow multiple waves of low pressure to lift up along a
frontal zone draped across the region. The 12Z UKMET is an outlier
in being too strong with the convectively induced wave lifting up
from the Arklatex region early Thursday and into the OH Valley on
Friday. The remaining guidance is fairly well clustered on the
idea of at least a modest low center. A separate low pressure
center will also be noted a bit farther north up across the lower
Great Lakes region. The 12Z CMC is a bit of a northerly outlier
with the evolution of this system. Finally, the arrival of yet
another shortwave impulse and associated low center will track
from the lower MS Valley to the Mid-Atlantic region Friday through
Saturday. The 00Z GFS tracks this wave overall a little north of
the model consensus, with the 12Z CMC a bit farther south. The GFS
though did trend a bit farther south, and is actually fairly close
to the 12Z ECENS mean solution which is noted to be a bit faster
than the 12Z ECMWF. Based on the latest degree of model
clustering, and ensemble support, a blend of the 00Z GFS, 12Z
ECMWF and 12Z ECENS mean will be preferred.


...Low to mid-level trough impacting the FL Peninsula...
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Preference: General model blend
Confidence: Average

The models take a low to mid-level trough near the Bahamas off to
the northwest over the next day or so and gradually recurve this
system around the western periphery of a weakening subtropical
ridge off the Southeast coast. The guidance overall hints at there
being a weak surface low that forms as the energy reaches the FL
Peninsula later Thursday afternoon, before then recurving on
Friday back off the Southeast coast. The 00Z NAM and 12Z UKMET
suggest some intensification of the low center east of the
Carolinas on Saturday as the system accelerates off to the
northeast. A general model blend will be preferred at this time
with this system.


...Southern stream closed low approaching CA...
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Preference: 12Z UKMET
Confidence: Slightly above average

The guidance allows for a southern stream closed low to approach
central/southern CA by late Saturday and into Sunday. The 00Z GFS
is the most progressive solution, while the 12Z ECMWF is the
slowest. The 00Z NAM, 12Z CMC and 12Z UKMET split the difference,
but the NAM and CMC both appear a tad too weak when compared to
the GEFS and ECENS member output. The 12Z UKMET for now appears to
be approximate the model consensus and has better ensemble
support, so will lean toward this solution.


...Height falls traversing the northern Plains/Midwest...
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Preference: General model blend...through 36 hours
            12Z ECMWF/ECENS mean blend...after 36 hours
Confidence: Average

A series of northern stream troughs will cross the northern Plains
and upper Midwest through the period. There is good agreement with
the initial energy lifting northeast across the upper Midwest on
Thursday. A second impulse crosses the northern Plains and upper
Midwest on Friday, with the 12Z CMC being a strong outlier with
this system. Then the guidance supports a closed low feature
crossing southern Canada on Saturday and Sunday which will allow
drive a cold front southeast down across the Midwest. The 00Z GFS
and 00Z NAM both end up on the slower side of the model spectrum,
with the 12Z non-NCEP models all more progressive. The 12Z ECMWF
and the 12Z ECENS mean overall best approximate the model
consensus with this last feature. Will prefer a general model
blend through 36 hours, and then lean toward a ECMWF/ECENS mean
blend thereafter.


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

Orrison