Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1205 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 Initial Model Evaluation...with Preliminary Preferences and
Confidence
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Closed low/upper trough over the Pacific Northwest
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Preference: 12Z ECMWF/18Z 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 12Z UKMET is
slightly slower than the model consensus. 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 12Z euro and 18Z
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
non-NAM consensus
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.
Low pressure reaching California on Saturday
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Preference: 12Z ECMWF/18Z 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 the UKMET and GEFS mean have a slightly northern
track with the surface low, and the NAM slightly faster than the
consensus. The 12Z euro and 18Z 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, and the CMC appears
too low with these heights over the southern tier of the U.S.
With no major differences noted among the NAM, GFS, and 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