Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1113 PM EST Tue Mar 05 2019
Valid Mar 06/0000 UTC thru Mar 09/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation Including Preference and Confidence
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...Deep trough over the Great Lakes/Northeast...
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Preference: General model blend
Confidence: Above average
WV loop shows broad trof crossing the Great Lakes currently that
will continue the progress through New England with little
fanfare. Likewise, an amplifying kicker shortwave currently
forming in N Manitoba will be the last vestige of the large
scale/global trof over the Northeast American continent to affect
the CONUS late Wed into the far NW Great Lakes. Like the wave
before, the guidance is very agreeable and sensible weather is
fairly quiescent with exception downstream of open lakes (i.e.
Lake Effect snows). A general model blend is supported at above
average confidence.
...Deep closed low center near 32N 143W...
...Arriving across CA by Wed...
...Shearing downstream across the central Plains on Thurs...
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Preference: Non-NAM blend (weight to ECMWF/CMC)
Confidence: Slightly above average
Currently a solid shortwave trough is affecting the West Coast
with a strong warm conveyor directed at southern CA. Guidance is
in fairly solid agreement with maintaining the strength of the
warm conveyor though the Great Basin into the Central Rockies
eventually leading to an axis of warm advection snows across the
Central Plains by Thursday, as the shortwave shears into
increasingly confluent/zonal flow across the Ohio Valley by late
Thurs/Fri. The 00z NAM continues to be most amplified and is
resistant to shearing the inner core of the wave, making it less
desirable in the blend. By Friday evening into Saturday, the GFS
and UKMET both show reduced phasing (spaced further away) with a
strong polar stream wave clipping the Great Lakes compared to the
CMC/ECMWF and bulk of ensemble guidance (and longer term trend).
As such would favor higher weighting toward the ECMWF/CMC in a
non-NAM blend for this system at slightly above average
confidence.
...Closed low in Pacific Northwest
...Progressive Trof reaching West Coast late Thurs/early Fri...
...Phasing through Rockies with deep Plains surface low Sat...
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Preference: 00z GFS and 12z ECMWF/CMC blend
Confidence: Average
Concentric closed low over the Northwest will track eastward while
an under-cutting shortwave/jet carves out a trof off the west
coast by late Thurs into Friday. Models have come into fairly
solid agreement with the timing/orientation of the wave, though
both the 00z NAM and the 12z UKMET are a bit sharper and deeper
with this trof. As the wave progresses ashore, the closed low
also starts stretching with a deepening of the eastern side as it
crosses the Southern Canadian Rockies. The UKMET and NAM, remain
very strong with the upstream (western) portion of the closed low
and start some binary interaction/stretching of the northern
portion of the southern trough, delaying its crossing of the
Central and Southern Rockies Sat. The orientation of the western
portion of the closed low with the southern stream support solid
model consensus of the wave ejecting with negative tilt and highly
favorable upper level pattern for rapid surface cyclogenesis by
12z Sat in KS. While the ECMWF shows some slower northern stream
wave increasing the stretching of the southern stream trof,
weakening the SE portion of the wave, relative to the GFS/CMC...
it is fairly minor given all the internal mesoscale features, jet
structure. So while there is fairly strong GFS/CMC/ECMWF
agreement, including a tightening ensemble (GEFS/CMCE/ECENS)
suite, there is only average confidence in the blend. This is due
to much of the energy features remain upstream of the best data
network in the Pacific at this time, as well as upscale synoptic
mass fields are contingent on the smaller scale internal
interactions that are quite uncertain and vary with each model
run.
...Next Pacific trough and surface low nearing Central West Coast
Sat...
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Preference: Non-CMC (weight to GFS/NAM)
Confidence: Average
On the heels of the last system, another shortwave is shed
eastward out of the strong/northward lifting flow across the
Alaskan Peninsula and Northwest Gulf of AK. Ensemble trends have
been favoring eventual slowing, supporting a broadening more
concentric trough that sets up off the Central West Coast by the
end of the forecast period, supporting a fairly strong surface
reflection as well. The 12z CMC is the clear outlier, supporting
a very strong/compact closed low on the NW periphery of the
guidance suite. While the ECMWF/UKMET both are slightly north
(with the UKMET faster) of the GFS and NAM. The overall cycle to
cycle trend favors the GFS/NAM slightly. As a slight hedge, will
support a 00z GFS/NAM weighted, non-CMC blend at average
confidence.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Gallina