Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1148 AM EST Thu Mar 07 2019
Valid Mar 07/1200 UTC thru Mar 11/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z Model Evaluation Including Preference and Confidence
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...Closed low in Pacific the Northwest, breaking into two with
eastward progression...
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Preference: 00z ECMWF/CMC, 12z GFS blend
Confidence: Average
A closed low over the Pacific Northwest will begin to break down
in the next 24 hours. Two pieces of energy then will split, one of
which is expected to become absorbed with a system tracking
through Alberta/Saskatchewan. There is rather good model agreement
on that scenario of the forecast. Differences on that other piece
of energy are more substantial and it is more complex with the
other approaching trough from the eastern Pacific. Some models
shear it out, taking even smaller pieces eastward across the
northern Rockies while others stall/close off more then eventually
wait for the west coast trough to absorb it. It seems the
consensus for the latter solution, which would favor the ECMWF/CMC
more though the 12z GFS does show this happening somewhat as well.
...Upper Midwest Deepening Surface Low This Weekend...
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Preference: 00z ECMWF/CMC, 12z GFS blend
Confidence: Slightly below average
A positively tilted shortwave will enter the Southwest tonight 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. As the cyclone deepens toward the
Upper Midwest, a swath of heavy precipitation will develop across
portions of the Dakotas, MN, and WI Saturday into Sunday. Overall,
model agreement is fair though there are still spatial differences
in the low track that will introduce precipitation type
differences across IA/MN/WI. The GFS and NAM are on the
northern/northwest side of the forecast envelope, with its low
position at 10.00z across southeast Minnesota and also is a bit
faster compared to the rest of the models. Meanwhile, the UKMET is
the southern solution, having its low across southern IA at the
same time. The 00z ECMWF/CMC remain in the middle, though are
slightly tilted toward the northern solutions at this time. The
cyclone then quickly moves into the UP of MI. The UKMET upper
level trough is the most different compared to the rest of the
deterministic and ensemble guidance.
Based on this, a blend of the ECMWF/CMC with some inclusion of the
GFS is preferred at this time.
...Next Pacific trough and surface low nearing Central West Coast
Sat...
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Preference: 00z ECMWF/UKMET, 12z GFS blend
Confidence: Average
Several pieces of energy coming out of the eastern Pacific will
eventually carve out a deeper trough over the west coast late in
the weekend. In the larger scale sense, the models are in pretty
good agreement with the evolution though there are some
differences noted with the individual shortwaves as well as how
much energy closes off over California. The GFS/NAM remain closest
to the coast with the main upper level low and also close off the
feature while the CMC/UKMET are further offshore/open and further
removed from the northern stream energy.
At the surface, a low approaches the northern California coast by
Saturday afternoon then stalls out before dropping down the coast.
Through 09.18z models are in good agreement but diverge quite a
bit after that with the low track. The NAM/GFS take it more
onshore while the ECMWF/UKMET/CMC are further offshore, especially
the CMC which is an outlier in this case.
As such, will lean on a ECMWF/UKMET/GFS blend at this point,
noting that there is increasing model spread Sunday onward.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Taylor