Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
124 PM EST Fri Nov 22 2019
Valid Nov 22/1200 UTC thru Nov 26/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z Model Evaluation with Preferences and Confidence
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...Cycling closed low emerging into Plains Today, potentially
phases with northern stream shortwave across Great Lakes Sat into
Sun supporting associated surface low moving from the lower out of
Tennessee Valley into the central Appalachians Friday night into
Saturday...
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Preference: 06z GFS/12z ECMWF blend with 12z GEFS/00z ECENS
Confidence: Slightly below average
19z update: The 12z ECMWF trended a bit faster with this system
because it resolved the northern stream shortwave a bit deeper.
This puts it on par with the ECENS mean and initial preference.
This shift also help to remove the UKMET, which continues to be
very close to the coast and much wetter in the deformation zone to
blend with much confidence. As such will favor a 06z GFS/12z
ECMWF blend with the 12z GEFS/00z ECENS a very low weighting to
the 12z NAM. Confidence remains slightly below average given the
run to run volatility.
---Prior Discussion---
GOES WV suite depicts and elongated closed low over CO stretching
into the Plains supporting a surface wave across the Lower MS
Valley currently. This wave is expected to lift through the
Appalachians later today into tomorrow. With time, a shortwave
emerging from the Canadian Rockies comes through the Great Lakes
and supports negative tilt phasing that supports the transfer of a
new coastal low through New England. There remains large timing,
and even some depth/strength difference with the northern stream
wave which leads to different evolution to the surface wave after
24.12z. The 12z GFS changed again back toward a faster/increased
phased wave much like yesterday's 12z run. This is paired with
the CMC which is uncharacteristically fast. The CMC looks out of
place to the ensembles with this system and throughout the rest of
the CONUS. Given the best clustering of the ensemble members
(ECENS/GEFS/CMCE) is closer to the 06z GFS, think that is the
direction of the preference (given good continuity with the 00z
suite as well). The 00z ECWMF, however, is odd as it does not
present much to the northern stream shortwave, and so with reduced
phasing/kicking of the southern stream wave, after 25.00z it
starts to occlude and wobble slowly through Gulf of Maine to Nova
Scotia, very slow even with the vast majority of ECENS members.
The 12z NAM is generally east of the best cluster but timed ok,
and the UKMET is west and eventually a bit slower, about half way
between the ECENS mean and the 00z ECMWF. As such will favor the
06z GFS/GEFS along with the 00z ECENS mean with some small
inclusion of the UKMET and NAM to account for some of the overall
variation. This uncertainty clearly affects the QPF and strength
of the deformation zone, so confidence is slightly below average
even this close in time.
...Embedded shortwaves within strong zonal northern Pacific Jet
into the Northwest...
...Associated surface wave across the Northern Tier by 00z Mon...
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Preference: 12z GFS/GEFS/ECMWF and 00z ECENS blend
Confidence: Average
19z update: The 12z ECMWF slowed with the development of the
Southern Canada surface wave toward early next week, perhaps too
slow as it is on the southwest edge of the ensemble suite. While,
the UKMET is further south and the CMC remains west, it seems a
good addition to the blend to replace the UKMET but still account
for some slower/southern track potential. As such will favor the
12z GFS/GEFS and the 00z ECENS mean with lower weight to the 12z
ECMWF.
Fairly active northern stream energy will bring a parade of
shortwaves across the northern tier of the U.S. during the short
term period while a large closed low drifts well offshore the
southern California coast. The large scale synoptic setup and
evolution is fairly represented by the various deterministic
models through about 48 hours, however, as the waves crest the
Canadian Rockies there is fairly sizable spread. This is
particularly the case with the CMC which is distinctly out of
place. Interestingly, the ECMWF, not presenting a shortwave in
the northern stream as strong as other guidance, leads to
downstream difference for this system, allowing it to accelerate a
to be a fast member of the ECENS suite. Perhaps, not egregiously,
but utilizing a slower ECENS mean (very close to the 12z GFS) and
the 06z GEFS , UKMET may help to stabilize some timing and overall
evolution to the system. The 12z NAM is a bit slower and north
than the remaining guidance, and while still clearly plausible, it
may be a bit too far off the best clustering to included at this
time. Given fast laminar flow out of the Pacific is notoriously
difficult to lock down, confidence is only average in a 12z
GFS/06z GEFS and 00z UKMET/ECENS mean blend.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Gallina