Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
229 AM EDT Mon Mar 11 2019
Valid Mar 11/0000 UTC thru Mar 14/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation Including Final Preferences and Confidence
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...Upper trough departing from the Great lakes/Northeast through
Monday night...
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Preference: General model blend
Confidence: Average
...07Z update...
No significant changes were noted in the 00Z ECMWF/UKMET/CMC
relative to their previous 12Z cycles.
...previous text follows...
Only minor differences remain with this system, with a general
model blend recommended to smooth out any smaller scale
discrepancies.
...Large closed low forming just offshore of California this
morning and tracking through Arizona/New Mexico, reaching Kansas
on Wednesday...
...Associated deep surface low in the Central Plains on
Wednesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 00Z GFS/ECMWF blend
Confidence: Slightly above average
...07Z update...
No significant changes were noted in the 00Z ECMWF/UKMET/CMC
relative to their previous 12Z cycles. The 00Z CMC continues to
stand out with its 500 mb progression across the Great Plains
while the 00Z ECMWF backed off on the amplitude of the
secondary/kicker shortwave in the Southwest leading to a slightly
slower ejection of the surface low through Kansas and Nebraska. No
changes are recommended based on the latest guidance.
...previous text follows...
The 12Z CMC stands out as a deterministic outlier but within the
ensemble spread concerning the track of its 500 mb low into New
Mexico by Wednesday morning. It appears an upstream wave,
discussed below, has some affect on the initial timing of the
negatively shortwave trough expected to reach the southern and
central Great Plains Wednesday morning. The flatter 12Z CMC across
the Southwest is also the slowest with the ejection of the lead
shortwave into the Great Plains. The 12Z ECMWF is a bit more
amplified across the Southwest Wednesday morning and a bit faster
to eject the lead shortwave into Kansas and Oklahoma, with the 00Z
NAM/GFS and 12Z UKMET somewhere in the middle.
The ECMWF ensembles have been fairly consistent, just a slight
slowing trend while the 12Z and 18Z GEFS members are noticeably
slower to bring the leading edge of the 552 dam height line at 500
mb into the Midwest on 00Z/14. The surface low track however,
shows remarkable agreement for a Day 3 forecast with the GEFS
members a bit south of the ECMWF members, with a favored middle
ground in line with a blend of the 00Z NAM, 00Z GFS, 12Z ECMWF and
12Z UKMET. Some of the timing differences noted aloft favors
simply a 00Z GFS/12Z ECMWF blend to place a a position within the
favored middle ground.
Ensemble heights at 500 mb show enough differences that confidence
is only slightly above average despite the very good surface low
agreement, meaning that shifts in the clustering are possible over
the next 24-48 hours.
...Progressive upper trough approaching the Pacific Northwest
Tuesday morning...
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Preference: non 00Z CMC blend
Confidence: Average
...07Z update...
As mentioned above, no significant changes were noted in the 00Z
ECMWF/UKMET/CMC meaning that the 00Z CMC continues to stand out as
a deterministic outlier with this system.
...previous text follows...
The 12Z CMC continued to favor a slower surface low track nearing
the central coast of British Columbia early this morning and worth
mentioning, this difference has little affect on weather across
the northwestern U.S. Amplitude differences with the mid-level
trough begin to show up over the western U.S. Tuesday night with
the 12Z CMC flatter and the 12Z ECMWF a bit deeper. This system
acts as a kicker to the lead shortwave discussed above, with the
past 4 12/00Z cycles of the ensemble guidance showing a slight
trend to be weaker through 12Z/13. At this time, better ensemble
support exists for a non 12Z CMC blend.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Otto