Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1135 AM EST Thu Jan 23 2020
Valid Jan 23/1200 UTC thru Jan 27/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z NAM/GFS Evaluation with Preferences and Forecast Confidence
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...Shortwave trough moving from the Pacific Northwest Fri into the
Plains Sat/Sat night...
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Preference: 12z GFS/00z ECMWF blend
Confidence: Average
The 12z NAM/GFS are close to the consensus bringing the next short
wave across the Pacific Northwest near 24/18z into the Northern
Rockies by 25/12z. After this time, the spread among the model
solutions increases, as the 12z NAM breaks down the mid level
ridging ahead of the short wave, dropping it much more quickly
into the Mid MS Valley by 27/00z.
By contrast, the 12z GFS maintains the mid level ridging across
the Northern Plains longer than the 12z NAM, though a bit faster
than the 00z ECMWF/00z GEFS mean. The 12z GFS closes off a mid
level low over ND/MN because of the faster movement, with the 00z
ECMWF/00z ECMWF mean remaining slower as the trough takes on a
negative tilt. Despite the differences, there is enough
commonality in the evolution of the system to recommend a blend of
the 12z GFS/00z ECMWF.
...Next shortwave trough moving onshore the West Coast by early
Sun...
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Preference: 12z GFS/00z ECMWF
Confidence: Average
The 12z NAM is fast with the short wave as it tracks from near 40N
133W at 26/00z into the Northern Rockies by 27/00z (as it the 00z
CMC). The 12z GFS is closer to the consensus with the timing of
the short wave energy as it reaches the Northern Rockies, which is
in good agreement with the 00z ECMWF mean/00z GEFS mean. Based on
the above, a 12z GFS/00z ECMWF blend is preferred, supported by
the ensemble mean of each model.
...Closed mid level low tracking from the Central Plains across
Ohio Valley Sat into the Northeast Sun...
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Preference: 12z GFS/00z ECMWF
Confidence: Average
The 12z NAM/GFS are in good agreement with the consensus bringing
the closed mid level low over the Central Plains this afternoon
into the OH Valley during Day 2 (about 26/00z). After that time,
the 12z NAM slows with the mid level system, despite its
downstream ridging being close to the consensus. Short wave energy
that the 12z NAM drops into the Mid MS Valley during this time
appears to carve out a long wave trough more quickly over this
area, slowing the mid level system over the Northeast during Day
3.
The 12z GFS remains close to the consensus with the track and
intensity of the mid level low as it moves into the Northeast
during Day 3 (by 27/00z). As a result, the 12z GFS is close to the
00z ECMWF/00z ECMWF mean/00z GEFS mean. Though there is some
spread concerning how the secondary surface low develops among
these solutions through 26/12z, there is enough agreement by the
end of the period to recommend a blend of the 12z GFS/00z ECMWF.
The forecast confidence is only average because of the differences
in the details of the developing secondary low over New England
late on Day 2 into Day 3.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Hayes