Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
201 PM EST Tue Nov 19 2019
Valid Nov 19/1200 UTC thru Nov 23/0000 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: non-12Z NAM blend
Confidence: Average
...17Z update...
The most significant changes from the 12Z ECMWF/UKMET/CMC compared
to their previous 00Z cycles were with the closed low crossing the
Four Corners into the central Plains Thursday/Friday. The 12Z
ECMWF slowed down giving greater support to a non-12Z NAM blend.
The UKMET/CMC remained fairly consistent.
Elsewhere, there were some changes with the closed low shifting
down off of the West Coast as well, with the 12Z ECMWF shifting
closer to the coast but is quicker than most of the deterministic
guidance to track the low southward. The 12Z GFS/CMC are likely
closest to the latest/favored ensemble means while the 12Z NAM is
closest to the coast. The 12Z ECMWF and 12Z UKMET are acceptable
when included as part of a blend, excluding the 12Z NAM.
...previous discussion follows...
The large scale flow pattern across the lower 48 will undergo a
transition from troughing over the East to ridging along the East
Coast by Friday. Meanwhile across the West Coast, a series of
closed lows will affect portions of the western U.S.
Overall, a blend of the 12Z GFS, 06Z GEFS and 00Z UKMET will work
for all systems across the CONUS. One of the bigger differences
relates to a closed low located west of the Baja Peninsula at 12Z,
which will weaken as it tracks into the Southwestern U.S. on
Wednesday. A related surface low will track from the central
Plains into the Great Lakes region. At the same time, a northern
stream, positively tilted mid-level trough axis will approach the
upper Mississippi Valley from the west. Timing differences with
the positively tilted trough show up with this feature as it
tracks east toward New England mainly with the slower 12Z NAM.
Better agreement exists with the GEFS/ECMWF ensemble means and the
12Z GFS, 00Z ECMWF and 00Z UKMET.
Another closed low which tracks across southern California
Wednesday evening is expected to track eastward toward the
central/southern Plains with some weakening by Friday afternoon.
Ensemble spaghetti plots are showing trends toward a middle ground
solution, currently best represented by the 06Z GEFS, 12Z GFS and
00Z UKMET.
Lastly across the West Coast, an elongated mid-level trough axis
will approach the Pacific Northwest late Thursday, with splitting
into two parts. A strong majority of available guidance keeps the
northern split into southern Canada with little to no impacts on
the U.S. The southern split will track south off of the West Coast
with ensemble means favoring a middle ground between the extremes
of the deterministic guidance. In addition to the middle ground
ensemble means, the best representative deterministic guidance is
the the 00Z UKMET.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Otto