Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
237 PM EDT Fri May 10 2019

Valid May 10/1200 UTC thru May 14/0000 UTC

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

12Z NAM/GFS Evaluation with Preliminary Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
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Preference: non 12Z CMC blend
Confidence: Average

...19Z update...

Only small nudges in the direction of the previous preference (12Z
NAM/12Z GFS/00Z ECMWF blend) were noted with the 12Z
ECMWF/UKMET/CMC compared to their previous 00Z cycles. Perhaps the
12Z UKMET shifted greatest with the placement of the redeveloping
surface low offshore of the East Coast on Monday such that it can
be included in the overall preference. However, the 12Z CMC still
lacks sufficient strength with the core of the 500 mb low nearing
the eastern U.S. Monday so it will remain removed from the final
overall U.S. preference.

...previous discussion follows...

Some change in the upper pattern is expected over the next 3 days
as a closed low forms Saturday night over the Dakotas and tracks
eastward along with the associated trough axis through the Great
Lakes and Ohio Valley. This will occur downstream of ridging
currently in place across the Pacific Northwest which will
deamplify and shift east. Meanwhile, the closed low near the coast
of California this morning will likely reach western Texas by
Monday evening.

A somewhat complex evolution is expected with the surface
reflection of the northern stream system as a low nears the upper
Ohio Valley Saturday night and redevelopment offshore of the
Mid-Atlantic coast. The 12Z GFS is weaker with the surface-850 mb
reflection of the Ohio Valley wave, and appears a bit fast
compared to the consensus with the redevelopment off of the East
Coast. The 00Z ECMWF is stronger with the surface to 850 mb low
but timing appears reasonable. The 00Z UKMET/CMC do not match
ensemble guidance well with the northeastern quadrant of the U.S.
Through roughly 00Z/13, a 12Z NAM/00Z ECMWF blend appears best.

The guidance suggests a second surface wave will develop/intensify
on Monday off of the Mid-Atlantic coast, similar to the position
of the Sunday surface wave. The ECMWF ensembles and the 00Z ECMWF
are on the northern side of the guidance, while the 12Z NAM/GFS
are closest to the East Coast compared to most ECMWF/GEFS/CMC
ensemble members. A blend between the 12Z GFS, 12Z NAM and 00Z
ECMWF appears best with this feature.

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

Otto