Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
232 AM EDT Thu Sep 26 2019

Valid Sep 26/0000 UTC thru Sep 29/1200 UTC

...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...

00Z NAM/GFS Evaluation with Preferences and Forecast Confidence
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...Overall Pattern Across the CONUS...
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Preference: General Model Blend (weighted toward the 12z ECMWF
mean/18z GEFS mean)
Confidence: Slightly above average

The 00z NAM/GFS are in excellent agreement with each other and the
model consensus across much of the CONUS, as the digging trough
over the West forms a closed low over western OR into Saturday.
The strong closing mid level low induces a strong mid level ridge
across the southeast corner of the CONUS, reaching into the Mid
Atlantic states.

The main event is across the Pacific Northwest/Northern Rockies
over the next three days. Deep moisture in advance of the the
closing mid level system becomes involved in the strong upslope
flow between high pressure over western Canada and developing
surface low pressure over WY by 29/12z. There is very good
clustering with both of the these features, increasing confidence
for a significant system to impact the Northern Rockies.

There is some model spread concerning how quickly surface low
pressure over northern MN at 27/00z, which then tracks into
Ontario. With the 12z ECMWF/ECMWF ensemble mean slower than the
remainder of the guidance suite (including the 00z NAM/GFS). The
18z GEFS mean seems to be the best consensus with respect to the
surface low track, so that solution is preferred here.


Model trends at www.wpc.noaa.gov/html/model2.html
500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml

Hayes