Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1257 PM EDT Tue Mar 19 2019
Valid Mar 19/1200 UTC thru Mar 23/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z NAM/GFS Model Evaluation Including Preliminary Preferences and
Confidence
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...Trough and Developing Low in the East...
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Preference: Blend of 12Z GFS, 00Z ECMWF
Confidence: Average
Considerable model spread persists through Day 3 with guidance
still shifting the track of the coastal low expected to develop
off the Mid-Atlantic Wednesday night and move over the Northeast
through Friday. The 12Z GFS has trended slow and farther inland
which brings it into better agreement with the 00Z ECMWF
operational. However, notable spread in both the 06Z GEFS and 00Z
ECENS suggest uncertainty persists and further shifting of the
track can be expected. The model preference listed above was based
predominately around that system, but the preferred blend is
applicable elsewhere. The 12Z ECMWF and 00Z GFS are in reasonably
good agreement across most of the CONUS, and a blend of the two
should represent a consensus forecast close to ensemble means
(with an average amount of model spread).
The track of this low is sensitive to northern stream shortwaves
that will be interacting, including a phase on Thursday and of
particular concern is the reinforcing shortwave that reaches the
Great Lakes Thursday night which will influence the track of the
primary trough/low through Friday and where the phasing takes
place over the weekend (beyond the current Day 3 outlook). The
reinforcing northern stream shortwave is still faster in the 00Z
ECMWF than the 12Z GFS, though the difference has shrunk and hence
a much more similar track of middle and lower level components.
Furthermore, the intensity of the components are similar among the
GFS and ECMWF resulting in similar QPF magnitude. The 00Z UKMET
and CMC are considerably slower with this reinforcing trough and
allow the low to track well off the Carolina coast and remain
considerable outliers. The 12Z NAM is more intense with both
mid-level waves which results in similar tracks to the GFS and
ECMWF, but with much greater magnitude to the QPF (despite higher
central surface pressure). The preference remains with the
GFS/ECMWF with the caveat that much is still to be determined with
the timing and intensity of the interacting components of this
low.
...Low and approaching trough in the West...
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Preference: General Model Blend
Confidence: Above Average
An amplified/full-latitude trough currently off the West Coast
comes ashore tonight before closing into a low over the Desert SW
Thursday and swinging into the northern Rockies through Friday.
Good agreement is seen among the global guidance so far today with
this feature, so a general model blend is recommended.
The next trough approaches the West Coast late Friday with good
timing agreement among guidance with the arrival of QPF into CA. A
general model blend also holds for this second feature.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Jackson