Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
136 AM EST Wed Feb 26 2020
Valid Feb 26/0000 UTC thru Feb 29/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation with Final Preferences and Confidence
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...Eastern Half of North America...
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Preference: non 00Z CMC blend
Confidence: Average
...07Z update...
Only minor changes were noted with the 00Z ECMWF/UKMET/CMC
compared to their previous 12Z cycles across the eastern half of
the nation. The 00Z CMC continues to stand out from the remaining
model consensus and even deepened the secondary low along the
coast of Maine on Thursday, stronger than its previous 12Z run and
greater than the remaining deterministic guidance and the ensemble
means. The 00Z CMC also continues to differ with the placement of
the primary 700-500 mb low in southern Quebec.
...previous discussion follows...
A closed low over the southern/central Great Plains will open up
into a mid-level trough during the day on Wednesday and track
toward the Northeast for Thursday with a negatively titled axis in
the middle and upper levels. An upstream northern stream trough
will move across the upper Great lakes and phase with the energy
moving into New England. A corresponding surface low will rapidly
deepen as it tracks through Pennsylvania and New York Wednesday
night, with secondary low development likely along the northern
New England Coast on Thursday. After the system reaches maturity
and begins to weaken, a deep 500 mb low will anchor over southern
Quebec, setting up a favorable lake effect snow event downwind of
Lake Erie and Ontario.
The models have been flip flopping with the timing of the lead
shortwave crossing the Appalachians late Wednesday into Thursday
morning for the past few days. The differences are relatively
minor through Thursday morning, but the 12Z CMC begins to depart
from the remaining consensus on Thursday. The 12Z CMC ends up with
a larger 500 mb low compared to the latest ensemble consensus and
is also weaker with 850 mb flow across New York. The position of
the 12Z CMC 850-500 mb low center also differs from the remaining
model consensus, so a non 12Z CMC blend is preferred.
The non 12Z CMC guidance is not identical, but a blend of the
remaining guidance should help to smooth out smaller scale
differences. This blend holds true for a pair of weak mid-level
shortwaves diving southeastward through the Great Plains and into
the southern U.S. where a non 12Z CMC blend represents the middle
of the timing/position differences noted.
...Western U.S...
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Preference: General model blend
Confidence: Average
...07Z update...
The biggest change from the 00Z ECMWF/UKMET/CMC compared to their
previous 12Z cycles across the Northwest was from the 00Z CMC. The
00Z CMC adjusted faster and is now rather comparable to the
remaining deterministic guidance. In fact, the 00Z ECMWF and 00Z
UKMET also trended slightly faster, with the 00Z model consensus
is fairly good agreement on the timing of the shortwave and
related cold front.
...previous discussion follows...
A somewhat sharp mid-level shortwave will reach the Pacific
Northwest coast sometime late on Friday, tracking into the
northern U.S. Rockies and southern Canadian Rockies by Saturday
morning. The ensemble means are in relatively good agreement with
the timing of the trough but ensemble spread is modest. No clear
trends have been identified regarding timing, but there has been
general convergence toward the middle over the past 4 12/00Z
cycles.
The 12Z CMC is slower than the means, while the 00Z GFS is
slightly ahead. No model is an outlier with respect to the
individual ensemble members, but the 12Z CMC stands out the
greatest. A blend of the remaining models regarding timing and
strength is preferred.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Otto