Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
306 PM EDT Fri Apr 17 2020
Valid Apr 17/1200 UTC thru Apr 21/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z Model Evaluation with Final Preferences and Confidence
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...Short wave energy tracking from the Rockies to Southern New
England...
...Surface low pressure crossing the Ohio Valley into the northern
Mid Atlantic...
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Preference: 12Z NAM, 12Z ECMWF, 12Z UKMET blend
Confidence: Slightly above average
The models are in reasonable agreement with this system but minor
differences with the 12Z GFS having a stronger push of low level
warm air to the north into the Northeast early Friday night.
Beyond that point, the 12Z CMC becomes a bit slower and south of
the model consensus. A 12Z NAM, 12Z ECMWF, 12Z UKMET blend appears
to be the most reasonable.
...Short wave energy in the southern stream...
...Surface low tracking from the Southern Plains to the Mid
Atlantic coast...
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Preference: 12Z UKMET/ECMWF blend
Confidence: Slightly below average
An initial shortwave is expected to track east from southern CA
early on and weaken across the Four Corners region through
Saturday evening. A second shortwave will follow in the wake of
the first and track from the Southwest into the Southern Plains
early Sunday. Eventually as the shortwave approaches the East
Coast, surface low development is expected with deepening offshore
into Sunday night.
The models begin to diverge on timing with this feature, mainly
noted with the 850-700 mb layer during the day on Saturday. The
12Z GFS ends up more progressive compared to the remaining
consensus but the 12Z NAM is a bit fast as well. The 12Z
ECMWF/UKMET appear a better fit to the ensemble and remaining
deterministic consensus. As the surface low intensifies over the
western Atlantic, The track of the ensemble means is best suited
to a 12Z UKMET/ECMWF blend with the 12Z GFS track more offshore
given its more progressive lower-level wave. The 12Z NAM may have
some utility along the East Coast as well, but time periods
leading up to Sunday night are less desirable. The 12Z CMC is also
displaced far enough from the preference regarding low track
placement to exclude it at this time.
...Short wave energy in the northern stream from Manitoba into the
Upper Great Lakes...
...Attendant cold front crossing the Northern Plains into the
Upper Great Lakes...
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Preference: 12Z ECMWF/UKMET blend
Confidence: average
Both the 12z NAM/GFS are displaced in timing from the middle
ground with the 12Z NAM a bit slower and 12Z GFS a bit faster as a
cold front sweeps across the Great Lakes region. The 12Z
ECMWF/UKMET appear to be a better compromise and are in agreement
with the preference for the southern stream system discussed in
the above section.
...Compact shortwave over the Pacific Northwest Sat into Sun...
...Approaching shortwave into the
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Preference: 12Z GFS/ECMWF/UKMET blend
Confidence: Slightly below average
Large differences develop with an approaching shortwave into the
West Coast on Monday with model agreement poor. The ensemble
means, however, show a similar depiction and so deterministic
guidance matching the means will be favored. Worth noting though,
the 12Z ECMWF shifted toward the 12Z UKMET (consistent with 00Z
UKMET) across the West by 00Z/21. The 12Z CMC also shifted in that
direction to some degree which is a trend that will be included
for the final preference.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Otto