Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1152 AM EST Sun Nov 11 2018

Valid Nov 11/1200 UTC thru Nov 15/0000 UTC

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

12Z NAM/GFS Evaluation...with Preliminary Preferences and
Confidence
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...Overall Pattern Across the CONUS...
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Preference: 75% 00Z ECMWF / 25% 12Z GFS blend
Confidence: Average

The upper level flow across the CONUS initially features a deep
layer ridge just off the West Coast with a downstream longwave
trough across the central U.S. with two amplifying shortwaves
diving south through the Intermountain West. Over the next 1-2
days, the mean layer troughing over the central U.S. will shift
east with two components, a northern stream and a southern
stream...with the southern stream getting left behind over the
south-central U.S. Tuesday into Wednesday. Across the West, the
northern end of ridging will be cut into by a shortwave trough
Tuesday and Wednesday associated with a cold front at the surface
reaching the Pacific Northwest.

At the surface, a low will hug the western and central Gulf Coast
tonight through Monday night at which point cyclogenesis will take
place along the northern Mid-Atlantic coast. The surface low will
deepen while tracking along the New England coast on Tuesday,
quickly exiting into the Canadian Maritimes by Wednesday morning.

Trends since yesterday have favored more separation between the
northern and southern stream components of the longwave trough
over the central U.S. with the GFS/GEFS representing the faster
side of the spectrum. Ensemble spaghetti height plots and scatter
low plots support a position nearest to the 00Z ECMWF with both
the surface low tracking up the East Coast and with the southern
stream closed low over the south-central U.S. Ensemble spread is
modest by 00Z/15 but shows more room to edge west of the GFS/ECMWF
than east.

The overall model preference is to be near the 00Z ECMWF but to
include a small fraction of the 12Z GFS given some of the dramatic
shifts in guidance since yesterday and to avoid too much of a
windshield washer effect if the models decide to trend back
east/faster again. Across the Northwest, a general model blend is
sufficient given differences in the surface to 500 mb pattern
provide more of a sensible weather impact to British Columbia than
Washington/Oregon.


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

Otto