Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1127 PM EST Thu Feb 28 2019
Valid Mar 01/0000 UTC thru Mar 04/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation Including Preference and Forecast Confidence
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...Phasing across Northeast/Coastal surface cyclone Sat/Sun
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Preference: 12z UKMET/ECMWF blend
Confidence: Slightly below average
Complex confluence of mid-level shortwave energy fairly rapidly
deepens surface cyclone off the Mid-Atlantic Coast clipping SE New
England. Broadly zonal pattern over the CONUS transports
shortwave energy out of the closed low in WA across the Northern
Plains and Great Lakes by early Saturday. Southern shortwave and
associated surface wave slide out of the TN Valley, into the
Mid-Atlantic. The southern stream wave deepens the surface wave
off the Mid-Atlantic coast. As the northern stream shortwave
elongates to phase with the wave, difference in timing and
orientation to the southern stream lead to moderate to high model
spread. Ensemble spaghetti analysis depicts a fairly steady state
ECMWF/ECENS solution slowly adjusting westward while other
guidance has been very inconsistent but trending toward it.
Clear outliers remain: the 00z NAM, which does not depict much of
the northern stream energy (mainly sheared out into the zonal
flow) eventually shunting the deepening surface wave well east of
the cluster; the 12z CMC shows greater amplification in both
streams but the southern stream is further east, having not
trended like other guidance.
The 12z ECMWF, like prior runs, has been on the southeast side of
the ECENS cluster but is also generally slower with the northern
stream wave, leading to reduced iteration initially (compared to
other deterministic runs, esp. GFS). As the wave deepens, it is
slowest to eject eastward and may be a bit too slow. The 00z GFS,
like the 18z run, continues a sizable shift westward with a
stronger/faster deepening surface wave near or just inside the
benchmark receiving much of the deepening through upscale growth.
While there is increased low level theta-e, this may be a bit too
aggressive, especially without other guidance support. The 12z
UKMET would be most middle ground and shows a similar evolution to
the ECMWF, but more favorably faster than the EC. All considered,
will favor the 12z UKMET and ECMWF, but with the GFS trend/upscale
enhancement there is a growing uncertainty in the preference as
the overall mass field setup deems the GFS/GEFS solutions
remaining plausible (even if not favored), making confidence is
slightly below average.
...Progressive West Coast Low (Sat), Lower Red/MS Valley by Sun
and Amplifying along East Coast by Mon...
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Preference: 12z UKMET/CMC
Confidence: Slightly below average
The closed low over the Northwest US will help direct progressive
southern stream shortwave energy into Central/Southern CA later in
the day Saturday, while shearing into increasing zonal flow across
the Rockies and Northern Plains. There is fairly good agreement
in the timing of the Pacific wave though the 00z NAM appears a bit
too amplified, and retains the strength of the wave even though it
is flat across KS into the Ohio Valley making it a bit less
preferred. The remaining guidance is fairly agreeable with the
shortwave progressing into the Southern Plains, but there is
fairly sizable difference in the placement of the surface front
and upglide/convective development in the Lower Red
River/Mississippi River Valley by early Sunday. The ECMWF is
furthest north with greatest vertical angle to the isentropic
ascent gradient supporting a more consolidated QPF response. This
seems a bit unlikely this early in the season, given displacement
from the warm Gulf without great warm air advection ahead of
deepening/amplifying system. The 00z GFS, on the other side of
the guidance, suggests a frontal zone very close to the Gulf with
a secondary QPF maxima in the deformation zone further aloft in
the Ozarks. This also seems a bit too dramatic for preference,
especially considering how fast the GFS gets across the southeast
into the Mid-Atlantic by Monday. More middle ground, in both
latitude and timing are the 12z UKMET and CMC. By late Sunday,
there is some typical timing difference with greater northern
stream phasing (faster) with the UKMET compared to the CMC.
Still, a compromise between the two seem appropriate though
moderate spread keeps confidence in this blend (especially by Day
3) to slightly below average.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Gallina