Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1148 AM EST Sat Nov 17 2018

Valid Nov 17/1200 UTC thru Nov 21/0000 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: 12Z GFS/00Z ECMWF blend, leading more toward the 12Z
GFS  toward 00Z/20 and 00Z/21
Confidence: Average

A broad mid-upper level trough across the northern two-thirds of
the nation, preceded by an anomalous ridge offshore of the Pacific
Northwest starts off the synoptic scale pattern over the lower 48.
Over the next three days, these large scale features will shift
east as mid-upper level troughing amplifies in the eastern U.S.,
while the ridge in the eastern Pacific moves into the Great Basin
and weakens a bit. A closed mid-level low currently well offshore
of the West Coast will open up into a positively tilted trough as
it makes landfall across southern CA/northern Baja Tuesday
morning.

At the surface, a pair of cold fronts will move through the Ohio
Valley with low pressure organizing off of the northern
Mid-Atlantic and New England coasts. Ensemble scatter low plots
have trended (past 4 12Z/00Z cycles) in the direction of the
40N/70W benchmark but there remains significant spread in location
valid 12Z/20. The 12Z NAM is a bit sharper with the upper trough
over the Ohio Valley and tucks the surface low closest to the
coast of Maine and while not an outlier, is in the minority of
ensemble and deterministic guidance. The 12Z GFS looks reasonable
here when blended slightly with the 00Z ECMWF given the 00Z ECMWF
is displaced much farther east compared to the remaining model
guidance, and it has been trending westward and has a weak surface
low hinted near the 12Z GFS.

Across the western Gulf of Mexico, the 00Z ECMWF is farther west
with a weak surface wave compared to the remaining guidance on
Monday into Tuesday, with even its own ensemble mean farther to
the east Tuesday morning. A non-00Z ECMWF blend appears best near
the Gulf.

Elsewhere across the lower 48, a GFS/ECMWF blend is reasonable
given some differences from the consensus seen across the West and
East from the 00Z UKMET/CMC.


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

Otto