Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1122 PM EST Wed Dec 25 2019
Valid Dec 26/0000 UTC thru Dec 29/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z NAM/GFS Evaluation with preliminary preferences/confidence
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NAM/GFS initialization errors do not seem to degrade their short
range forecasts.
System approaching Pacific Northwest Sunday morning
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Preference: GFS/UKMET compromise
Confidence: Above average
There are competing factors clouding the forecast picture across
the Pacific Northwest and Plains/Midwest by Sunday. A system
approaching the Pacific Northwest at that time has a building
ridge seen in all the guidance in its wake, which should yield a
strengthening system aloft moving towards the region. The 12z
ECMWF was out of tolerance with this system as it moved a sharp
shortwave out in advance of it which was not seen in any of the
other guidance and likely led to too weak of a look with the
system near 47N 130W Sunday morning (even when compared to its
ensemble mean). A compromise of the 00z GFS/12z UKMET looks ideal
with the Northwest system with above average confidence.
System moving from the West into the Midwest Fri-Sun
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Preference: ECMWF/UKMET/Canadian compromise
Confidence: Average
Downstream, the guidance is plagued with stream interaction as the
system moving from the West into the Plains starts out unphased
but becomes phased with time as a sharply amplified ridge building
into western Canada. The quickest solutions with the
Plains/Midwest system are the 00z GFS and 00z NAM. Since the flow
overall is becoming more amplified, a slower solution in the
Plains/Midwest is preferred by Sunday morning since the kicking
influence of the system approaching the Pacific Northwest
shouldn't be felt quite yet (over 15 degrees latitude/900 miles
away). Prefer a compromise of the 12z ECMWF/12z UKMET/12z
Canadian with the Plains/Midwestern system with average confidence.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Roth