Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1239 AM EDT Wed Mar 20 2019
Valid Mar 20/0000 UTC thru Mar 23/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation Including Preferences and Confidence
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...Trough and Developing Low in the East...
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Preference: Blend of 00Z GFS and 12Z ECMWF
Confidence: Average
Considerable model spread continues with the evolution of a strong
low developing in the Northeast late this week. Complexity is
added by two phasing events: (1) on Thursday with a southern
stream shortwave and another wave digging sharply through the
Great Lakes, and (2) on Friday when more substantial cyclogenesis
will begin over the Northeast. At that point the initial shortwave
will be ejecting in a negatively tilted fashion up the coast and
will phase with yet another sharply digging shortwave from the
Great Lakes. Subtle detail differences in this sequence of events
do lead to some important variation in the strength and timing of
the low.
In general, the NCEP models (00Z NAM and GFS, 18Z GEFS) are on the
faster end of the spread; by 12Z Friday the GFS has the surface
low further north than over 90 percent of ECMWF ensemble members.
The 12Z ECMWF is actually faster than the associated ECMWF
Ensemble Mean, 12Z CMC and 12Z UKMET, but all of these models are
on the slower end of the spread. For now, the preference was to
opt for a blend in timing between the GFS and ECMWF, which are in
the middle of the deterministic model spread and should provide
something close to a median forecast in terms of timing. However,
given the considerable number of ECMWF ensemble members slower
than even the deterministic ECMWF, it should be noted that the
timing could slow down further than the official forecast.
...Remainder of the CONUS...
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Preference: General Model Blend
Confidence: Above Average
Elsewhere across the CONUS, models are generally in good
agreement, with relatively low model spread. The preference in
these regions is for a general model blend. The biggest
differences appear to be with the amplitude of the trough on
Friday as it begins to kick out of the West. This leads to larger
height spreads aloft over Arizona, New Mexico and Texas. The NCEP
models generally show more amplification, which leads to higher
QPF.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Lamers