Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1253 PM EDT Thu Apr 30 2020
Valid Apr 30/1200 UTC thru May 04/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z Model Evaluation Including Preliminary Preferences and
Confidence
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...Deep trough/closed low impacting the East through Friday and
early Saturday...
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Preference: 00Z ECMWF/EC Ensemble Mean/CMC blend
Confidence: Average
The 12Z GFS continued to be on the faster side of the guidance in
bringing a shortwave on the eastern edge of the mid-level trough
ejecting of the eastern U.S. as well as being faster to bring a
second vorticity center towards New England on Friday. The NAM
was also inclined to stick with its southward-displaced trough
like it showed in its 30/00Z run. Both features were outliers
with the mid-level trough axis by 12Z Saturday compared to all of
the ECMWF/GEFS/CMC ensemble members. Removed the 30/00Z UKMET from
the choice given its very slow progression.
...Shortwave crossing the Northwest today and moving into western
Ontario Saturday morning...
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Preference: 30/00Z ECMWF/UKMET/CMC blend
Confidence: Slightly above average
The GFS from the 30/12Z run still stands out the greatest with a
more amplified and slower 500 mb shortwave track by mid-day
Friday...which still puts it at odds with trends from the 30/00Z
ECMWF and 30/00Z CMC (those non-NCEP models were showing some
trends toward that general solution but there were just not as
extreme). The lower mid-level heights in the GFS also made it
easy for a second shortwave originiating in northern Saskatchewan
to drop southeastward and produce a deepening closed mid-level low
over Ontario and Quebec by early Sunday. At this point, thinking
is that a 30/00Z ECMWF/UKMET/CMC blend will incorporate some of
these ideas which fall between the northern and faster 30/12Z NAM
and southern 30/12Z GFS.
...700-500 mb shortwave reaching the central Plains Saturday
morning...
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Preference: 30/00Z ECMWF/UKMET/CMC blend
Confidence: Below average
The 30/12Z NCEP runs were similar to their previous runs...meaning
that they were south with this feature compared with the 30/00Z
runs of non-NCEP guidance. The latest ensemble spaghetti plots
still offer more support to the non-NCEP guidance at this point.
No change to the overall preference was made. This feature will be
occurring in a post-frontal environment with upslope flow just
above the surface. Convective uncertainty lowers confidence with
this feature but a Southern Plains surface low now shows good
model agreement from the latest available models.
...Deep trough offshore the West Coast by Saturday...
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Preference: non 30/00Z UKMET blend
Confidence: Average
Ensemble means support a non 00Z UKMET blend with the approaching
large trough/closed low offshore of the Pacific Northwest early
Saturday. Despite the decent agreement from the 30/00Z models and
the 30/12Z run of NCEP models, ensemble spaghetti plots still show
some spread and room for future adjustments with later
deterministic guidance.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Bann