Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
100 PM EDT Fri Mar 13 2020
Valid Mar 13/1200 UTC thru Mar 17/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z NAM/GFS Evaluation with Preliminary Preferences and Confidence
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...Closed Low developing over Pacific NW through Saturday...
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Preference: General model blend through 00Z/16
non-12Z GFS blend 00Z/16 - 00Z/17
Confidence: Slightly above average
Model differences remain small until Sunday evening when the 12Z
GFS ends up farther south with the 700-500 mb low off of the West
Coast. The 12Z GFS is not an outlier when considering the
available ensemble guidance but given greater support for a
non-GFS solution by Sunday, the preliminary preference will
exclude the 12Z GFS after 00Z/16.
...Weakening mid-level shortwave tracking through the Southwest
today, weakening across the Midwest late Saturday...
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Preference: Non-12Z NAM blend
Confidence: Slightly above average
Only minor timing/amplitude differences remain with the mid-level
shortwave as it tracks east through the OH Valley. The 12Z NAM, as
with previous cycles, continues to look too fast, however not by a
lot. A non-12Z NAM blend of guidance looks reasonable with this
system.
There are some latitude differences with the trailing front across
the southern states by Saturday into Sunday with a weaker surface
low noted in the 12Z GFS tracking across the Mississippi River
Valley allowing for a more southern-placed warm front. The GFS is
not an outlier, but there is less support for it among the
remaining deterministic guidance. Ensemble means support a middle
ground which can be represented by a general blend, removing the
faster timing of the 12Z NAM across the eastern U.S.
...Base of longwave trough over the north-central U.S. by Monday
evening...
...Related cold front across the Upper Midwest...
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Preference: Non-12Z GFS blend
Confidence: Average
The 12Z GFS stands out as the faster model with this system, a non
12Z GFS blend will be preferred given the remaining deterministic
and ensemble guidance (including the 06Z GEFS) is slower than the
12Z GFS.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Otto