Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1256 AM EDT Thu Oct 18 2018

Valid Oct 18/0000 UTC thru Oct 21/1200 UTC

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

00Z NAM/GFS evaluation...with preliminary preferences and
confidence
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...Overall Pattern Across the CONUS...
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Preference: 00Z GFS/12Z ECMWF blend...more weighted toward ECMWF
by Sunday
Confidence: Slightly above average

Across the western U.S., the mid-upper level pattern will remain
blocked with a quasi-rex block in place over the coast. An upper
low is forecast to develop by Friday morning along the central
California coast and remain in place while upper ridging
translates east from off of the Pacific Northwest today, to the
central High Plains for Sunday morning. The eastern U.S. will see
the departure of an upper level trough axis today, replaced by a
longwave trough east of the Mississippi Saturday and Sunday as a
closed low (currently over the Great Basin) continues to weaken
toward the east. At the surface, a couple of cold fronts will pass
through the central/eastern US, bringing reinforcing shots of
cooler air followed by sprawling high pressure for the weekend.

The models were in generally good agreement through Sunday but a
couple of differences are worth noting. The 00Z GFS was a bit
quicker with upper trough progression through the eastern U.S.
with the 12Z ECMWF lagging behind a bit due to slightly greater
ridging in the western Atlantic, but with the ECMWF closer to the
GEFS/EC means. While differences are small, a nudge toward the 12Z
ECMWF for the weekend is preferred given better agreement toward
the ensemble means.

Elsewhere, the 12Z UKMET/CMC were displaced northward from the 00Z
NAM, 00Z GFS and 12Z ECMWF with a 500 mb vorticity max moving
through the upper Midwest Saturday morning. The ensemble means
support a non 12Z UKMET/CMC blend.

Therefore, the overall preference is a 00Z GFS/12Z ECMWF blend but
with more ECMWF weighting toward the late Saturday into Sunday
time frame.

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

Otto