Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1225 AM EST Thu Mar 07 2019
Valid Mar 07/0000 UTC thru Mar 10/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z NAM/GFS Evaluation Including Preliminary Preference and
Confidence
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...Mid-level shortwave energy moving through the central U.S.
ridging Thursday night...
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Preference: 00Z NAM...00Z GFS...12Z CMC blend
Confidence: Slightly above average
The 12Z ECMWF is slightly slower/weaker with shortwave energy
across the Midwest, while the 12Z UKMET is a bit slower than the
consensus. The ensemble means show good agreement with one another
and the 00Z NAM, 00Z GFS and 12Z CMC.
...Closed low in Pacific the Northwest, breaking into two with
eastward progression...
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Preference: General model blend through 00Z/09
Near the 12Z ECMWF/UKMET after 00Z/09
Confidence: Average
Differences with a closed low in the Pacific Northwest begin to
appear near 00Z/09 with the 12Z UKMET and 00Z GFS slightly quicker
with the northern portion of this system tracking through southern
Alberta/Saskatchewan. The 00Z NAM is a bit of an outlier with the
southern portion of the closed low being more progressive. The
ensemble means are in good agreement and near the 12Z ECMWF and
the 12Z UKMET by 00Z/10 while the 00Z GFS ends up quicker.
Overall, while there is the potential for changes due to complex
interactions of the upper level features, a solution near the 12Z
ECMWF/UKMET and ensemble means is preferred at this time.
...Upper Midwest Deepening Surface Low This Weekend...
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Preference: 00Z NAM/12Z ECMWF blend through 12Z/09
near the 12Z ECMWF 12Z/09-12Z/10
Confidence: Slightly below average
A positively tilted shortwave will enter the Southwest Thursday
night and will track across the southern Rockies late Friday,
emerging as a negatively tilted shortwave in the Central Plains
for Saturday with a developing surface low. Overall trends in the
deterministic and ensemble guidance have been faster since the 12Z
cycle on Tuesday with the ECMWF making the smallest run to run
changes.
The 00Z GFS is the fastest and lies toward the fastest edge of the
ensemble guidance. Despite the trends, the GFS is not supported by
other deterministic guidance at this time which is a negative for
using the 00Z GFS. The 12Z UKMET differs with its handling of
shortwave energy in the base of the upper trough in the Southwest
on Friday with a sharper/stronger mid-level shortwave which
continues its track into west Texas and Oklahoma Saturday morning.
The difference in the 12Z UKMET's handling of shortwave energy
aloft affects its surface low track with a more southern/faster
low compared to the remaining model consensus. The 12Z ECMWF and
00Z NAM appear best until about 12Z/09 when the 00Z NAM becomes a
bit faster with the leading edge of the shortwave trough. The 12Z
CMC could be used as a second option to the 12Z ECMWF for Saturday
into Sunday.
...Next Pacific trough and surface low nearing Central West Coast
Sat...
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Preference: 00Z NAM, 00Z GFS, 12Z ECMWF blend
Confidence: Slightly above average
Another upper trough is expected to reach California by Sunday
morning with some timing differences noted in the latest guidance.
The 00Z NAM/GFS are faster with the 12Z UKMET/CMC slowest.
Ensemble guidance from Wednesday supported a slightly faster trend
leaving the 12Z UKMET/CMC toward the slower side of the guidance.
The 12Z ECMWF is near the middle to slower side of the ensemble
spaghetti heights but when blended with the 00Z NAM/GFS, a
reasonable compromise is reached.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Otto