Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
140 AM EST Mon Nov 26 2018

Valid Nov 26/0000 UTC thru Nov 29/1200 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...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: non 00Z UKMET blend
Confidence: Average

...07Z update...

Only minor adjustments were made out East and West from the latest
00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles. Out
West, while the 00Z UKMET/CMC adjusted toward the preliminary 00Z
NAM/GFS/12Z ECMWF preference, the 00Z UKMET's adjustment was small
enough to exclude it from the preference with the UKMET continuing
to be slower through Thursday morning.

...previous discussion below...

The upper pattern starts off rather amplified over the lower 48
with broad troughing off of the Pacific Northwest, followed by
sharp upper ridging over the Pacific Northwest into western Canada
and longwave troughing over the Great Lakes/Mid-Mississippi
Valley. A powerful shortwave responsible for ongoing blizzard
conditions over portions of the upper Midwest will track toward
the Northeast with secondary low development over New England
early Tuesday morning. Meanwhile a large closed low will form over
the Great Lakes and track eastward through Wednesday night as it
reaches Nova Scotia. The flow pattern over the western U.S. will
flatten into mid-week before the arrival of a powerful shortwave
to reach northern California early Thursday morning.

Out West, the biggest difference was with the approach of a strong
shortwave and surface low toward northern California early
Thursday morning. The 00Z GFS has held decent run to run
continuity over its past 3 cycles with a broad trend from the
other models toward the GFS since 3 cycles back. Ensembles show
the 12Z UKMET/CMC to be a bit slow and the ensemble scatter low
plots have been trending south valid 12Z Tuesday. While the 00Z
GFS is just south of the middle of the latest ensemble scatter low
plots, it has held good continuity and when blended with the 00Z
NAM and 12Z ECMWF, a favorable middle ground is reached.

The models were fairly agreeable with the evolution of the storm
system approaching the Great Lakes and redevelopment for New
England. Ensemble scatter low plots still show some room for
adjustment with the 00Z GFS/18Z GEFS along the western side of the
model spread Northeast early Tuesday but the trend since yesterday
has been to take the low farther inland. A general model blend
appears reasonable here.

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

Otto