Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
224 AM EDT Fri Mar 29 2019

Valid Mar 29/0000 UTC thru Apr 01/1200 UTC

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

00Z Model Evaluation With Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: Non-NAM blend...Central/Eastern U.S.
            00Z NAM/GFS/ECMWF blend...Western U.S.
Confidence: Slightly above average

The models are in good agreement in gradually weakening a deep
layer closed low offshore the Pacific Northwest as a portion of
this closed low will separate off to the east and inland across
the northern Great Basin and northern Rockies on Friday. This
energy will then eject southeast across the central Plains Friday
night and get caught up into the base of an amplifying northern
stream trough over the Midwest through Saturday. Although some
trailing energy/troughing related to the initial closed low is
expected get left behind back toward the Four Corners region
underneath a deep layer closed high center that drops southeast
from southwest Canada. By Sunday, the aforementioned northern
stream trough will cross the Great Lakes, OH Valley and Northeast
as the troughing over the Four Corners region settles south down
across the southern High Plains.
 
Overall, the models show rather good agreement with the large
scale evolution of the northern stream trough evolution, but the
00Z NAM does begin to lag the global models with the attendant
frontal zone that crosses the OH Valley by late Saturday and the
Mid-Atlantic and Northeast on Sunday. All of the models show at
least one surface wave ridging northeast up along the front too
which crosses the OH Valley and lower Great Lakes region. The 00Z
GFS overall is a touch faster than the global models, but there is
collectively more ensemble support for a more progressive solution
versus the NAM, so will prefer a non-NAM consensus with the larger
scale trough, front and surface wave.

By early Sunday, all of the guidance generally agrees with a weak
trough or closed low feature setting up over the Four Corners
region. The 00Z CMC solution did trend a bit stronger with this
cycle, but is still overall the weakest and fastest solution.
Every other model including the 00Z NAM/GFS solutions and the 00Z
UKMET/ECMWF solutions support a relatively deeper trough and
possibly a weak closed low dropping south with time across the
Four Corners region and then toward the southern High Plains
through Sunday into Monday. The UKMET though is the slowest
solution whereas the NAM, GFS and ECMWF are clustered in between
the faster CMC and slower UKMET. Given that the latest GEFS and
ECENS suites favor the stronger non-CMC consensus of solutions.
The best model clustering with this system still favors the NAM,
GFS and ECMWF, and so a blend of these solutions will continue to
be preferred with this system.


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

Orrison