Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1242 AM EDT Tue Mar 19 2019
Valid Mar 19/0000 UTC thru Mar 22/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation Including Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: Blend of 00Z GFS, 12Z ECMWF
Confidence: Average
The greatest amount of model spread over the next few days is
related to the coastal low expected to develop off the Mid
Atlantic and toward the Northeast. 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).
A notable trend with the Northeast coastal low over the past
several model cycles is toward (1) a stronger low and (2) a
position closer to the coastline. This is not an uncommon trend
several days in advance of nor'easters, and given that it is
present across multiple models, it seems realistic.
Ensemble sensitivity analysis of the low shows that the forecast
is sensitive to the upstream shortwaves that will be phasing. In
particular, the forecast is especially sensitive to the strength
of the northern stream wave that will dig into the Great Lakes on
Wednesday. Models that show a stronger northern stream wave (00Z
NAM, 12Z ECMWF) tend to show lower surface pressures off the
Northeast coast later in the week, and vice versa.
The intensity of the low remains a source of some uncertainty, but
the 00Z GFS and 12Z ECMWF show very similar low tracks. Their
forecast low positions are nearly on top of each other through
22.12Z, and are also nearly on top of the 18Z GEFS Mean and 12Z
ECMWF Ensemble Mean positions. A blend of these models is the
preference. Although the ECMWF shows a stronger northern stream
wave, the overall evolution is similar and consistent with
expected model trends in these scenarios. A blend of the two will
offer a compromise between a stronger scenario (ECMWF) and a
moderate-strength low (GFS).
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Lamers