Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
146 AM EST Thu Feb 28 2019
Valid Feb 28/0000 UTC thru Mar 3/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Final Model Evaluation...with Preferences and Confidence
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Closed low/upper trough over the Pacific Northwest
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Preference: 00Z ECMWF/00Z GEFS mean
Confidence: Near average
An upper level low and its surface low initially parked off the
Washington coast will be quite slow to move through Friday
morning, after which it begins evolving into an open wave over
Washington and Oregon and then tracks inland across the northern
Rockies. The models are in good agreement on this system through
Friday evening, with some slight differences noted in the CMC
regarding surface low placement. The 00Z GFS becomes slightly
faster with the trough progression whilst the 00Z NAM is slightly
more amplified with the trough axis. In terms of the upper low
dissipation, a few of the euro ensemble members keep the low
distinct whereas other model ensemble members have quickly
transitioned to an open wave. A blend of the 00Z euro and 00Z
GEFS mean provide a reasonable starting point for the forecast
here.
Closed upper low over southern Canada
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Preference: General model blend through Saturday morning, then 00Z
ECMWF/UKMET/CMC blend
Confidence: Above average
An elongated upper low tracking southward from central Canada is
forecast to consolidate into one main low centered over Manitoba
and Ontario by this weekend with a trough axis extending westward
near the Canadian border. This will send a strong arctic surface
high southward across the Plains by Sunday with well below normal
temperatures expected. The models are relatively well clustered,
and the main difference noted is that the NAM is not quite as far
south as the model consensus concerning upper low placement by
Saturday night and into Sunday. The GFS and the GEFS mean are
slightly farther south compared to the model consensus on Saturday.
Low pressure reaching California on Saturday
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Preference: 00Z ECMWF/00Z GEFS mean
Confidence: Near average
A rather potent southern stream shortwave and surface low tracking
eastward across the Pacific is progged to reach the California
around Saturday afternoon, bringing more additional heavy
precipitation to this region. Although this shortwave dampens
some by Sunday morning, it should continue its track across the
southern Rockies and then be the next big weather story for the
south-central U.S. just beyond this forecast period. The GFS
keeps the low amplified a little longer than the other models by
12Z Saturday and slightly slower, and the UKMET has a stronger
surface low. The 00Z euro and 00Z GEFS mean provide a reasonable
depiction of the storm track evolution for now.
Shortwave perturbations and low pressure systems across the
eastern U.S.
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Preference: 12Z ECMWF/00Z GFS/00Z NAM blend
Confidence: Near average
Quasi-zonal flow with low-amplitude perturbations will be present
from the Midwest to the Southeast coast through this forecast
period. The upper level pattern shows decent model agreement
through Friday afternoon. The UKMET has 500mb heights that are
likely too high over the Midwest by Saturday. The 00Z euro is
more amplified than the model consensus with the shortwave trough
over the east-central U.S. Friday night. With no major
differences noted among the NAM, GFS, and 12Z euro, a blend of
those models should suffice for now across this region.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Hamrick