Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1158 AM EST Wed Feb 28 2018

Valid Feb 28/1200 UTC thru Mar 04/0000 UTC

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

...12Z NAM/GFS evaluation along with preliminary preferences...
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...Shortwave over the Southwest, ejecting eastward into the Plains
tonight and reaching the East Coast late Thursday while
interacting with a northern stream wave dropping south from the
upper Mississippi valley...
...Resultant surface cyclone into the Ohio valley on Thursday with
surface low reforming southeast of the New England coast through
Friday morning...
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Preference: 50% 12Z NAM, 25% 12Z GFS, 25% 00Z ECMWF blend
Confidence: Average

00Z GEFS/ECMWF/CMC ensemble spaghetti heights at 534 dam continue
to show the GEFS and older runs of the GFS as stronger and on the
western edge of the available members valid Friday across the
Northeast. Ensemble trends in the heights and surface low plots
have shown a western shift valid 12Z/02 offshore of New England
with the GEFS members on the far northwestern edge and ECMWF
members the southeastern edge of the envelope of solutions. The
preference is to be near the centroid of the available ensemble
scatter low plot positions, considering trends, which is between
the 00Z GEFS and 00Z EC members, or near the 12Z NAM position
valid 12Z/02.

The 12Z GFS has come into better agreement with this preference
but continues to lie on the northern side of the guidance, while
the 00Z ECMWF is on the south side. Valid 00Z/03, the 12Z NAM ends
up on the western side of the ensemble spread, and despite trends
in that direction from the ensembles, blending with the farther
east 12Z GFS and 00Z ECMWF appears prudent. Regarding mass fields,
the 12Z NAM looks to be the closest of the deterministic models to
the preference, while the 12Z GFS and 00Z ECMWF are considered
secondary preferences given the 00Z UKMET/CMC appear too be
displaced in strength and/or position from the preference.

Differences with the low level thermal fields across the northern
Mid-Atlantic and Northeast show the 12Z NAM coldest with 12Z GFS
warmest and 00Z ECMWF somewhere in the middle of the two.

 
...Large closed low off of the Pacific Northwest by Thursday
evening...
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Preference: Non-00Z UKMET blend
Confidence: Slightly above average

Similar to yesterday, there continues to be good agreement with
this system. There have been some models that have trended a bit
slower compared to yesterday's runs, but ensembles continue to
show relatively good agreement, led by the consistent ECMWF mean.
Only the 00Z UKMET appears to deviate from the latest
deterministic models with a stronger surface low along/offshore of
the West Coast on Friday into Saturday. For that reason, a non-00Z
UKMET blend is recommended for this system.


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