Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
120 PM EDT Fri Mar 22 2019
Valid Mar 22/1200 UTC thru Mar 26/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z NAM/GFS Evaluation Including Preliminary Preferences and
Confidence
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...Mid-level shortwave trough axis crossing the West Coast
Saturday morning...
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Preference: non 00Z ECMWF blend
Confidence: Slightly above average
The 00Z ECMWF and its ensemble mean stood out from the remaining
deterministic/ensemble consensus with this feature making it
appear to be a less likely solution. The ECMWF is stronger and
more amplified with vorticity in the base of the trough and ends
up translating the southern portion of the upper trough into Utah
and Colorado whereas the remaining guidance lifts the energy north
into Montana. Trends do not favor the ECMWF solution but ensemble
spread remains fairly large at this point lowering confidence a
little below average.
...Closed low moving from the Central Plains on Saturday to the
East Coast on Monday while weakening with eastward extent...
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Preference: 12Z GFS, 00Z ECMWF, 00Z UKMET blend
Confidence: Average
Timing differences are noted with this feature with the 12Z
NAM/GFS faster than the 00Z ECMWF/UKMET/CMC showing up Sunday
morning. The 12Z NAM is fastest with the mid-level wave, while the
00Z CMC is slowest. None of these models are outside of the
ensemble spread and while a slight trend to be faster like the 12Z
NAM/GFS is warranted, do not want to go toward the extremes of the
model spread. A blend of the 12Z GFS, 00Z ECMWF/UKMET appears
reasonable.
Some caution is advised with the 00Z ECMWF beyond 12Z/25 from the
Lower Mississippi Valley into the Southeast given differences with
a shortwave referenced in the above section. The slower and more
amplified 00Z ECMWF across the South is slower to move moisture
out of the region.
...Closed low approaching the West Coast Trough and Coastal Low in
the East...
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Preference: 12Z GFS/00Z ECMWF blend (weighted toward ECMWF)
Confidence: Average
Timing differences are seen with the next system to reach the West
Coast on Monday. Ensemble spaghetti height trends have a history
of showing the faster GFS/GEFS trending slower toward the ECMWF in
cases like this. Therefore, since we are again seeing a faster 12Z
NAM/GFS track with this system, and the amplified nature of the
flow in place, will recommend a slower solution between the 12Z
GFS/00Z ECMWF but with more weight toward the 00Z ECMWF.
...Remainder of the CONUS...
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Preference: General model blend
Confidence: Average
Systems elsewhere across the CONUS showed reasonable agreement
with just some minor timing differences. Therefore, a general
model blend is preferred outside of the three systems discussed
above.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Otto