Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
131 AM EST Fri Mar 01 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: 00z GEFS/UKMET/ECMWF/CMC blend
Confidence: Average
07z update: The shift westward and slightly deeper continues in
the late arriving guidance. The most significant shift was the
00z UKMET, with a deep almost convective upscale response,
(similar to the GFS), while slightly east of the GFS, it is in
line with the 00z GEFS mean. The 00z ECMWF shifted west but
remains very close to the 12z ECENS mean, east of the UKMET/GFS,
less amplified. This was further corroborated by the 00z CMC.
Clearly, the trend is deeper, but do not want to go as aggressive
as the GFS. As a compromise, will favor inclusion of the 00z
GEFS/UKMET with the CMC/ECMWF in the blend. With some reduction
of spread, there is increased confidence but only to average in
this blend.
---Prior Discussion---
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: 00z UKMET/CMC/ECMWF blend
Confidence: Average
07z update: Further slowing was noted in the non-NCEP guidance but
influence from a downstream deeper solution presses the trailing
frontal zone a bit further south. This allows for the ECMWF/UKMET
to shift southward relative to the 12z runs, with the UKMET
nearing the GFS axis. The CMC shows similar run to run continuity
but is bolstered by the ECMWF/UKMET. Some inclusion of the GFS
seems appropriate, especially on Day 1 into Day 2, but as the
system slides toward the East Coast and northern stream digging
influences lead to slightly faster timing, would still prefer to
hedge away by Monday. As such will favor a 00z ECMWF/UKMET/CMC
blend at average confidence.
---Prior Discussion---
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