Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
211 PM EST Tue Feb 12 2019

Valid Feb 12/1200 UTC thru Feb 16/0000 UTC

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

12Z Model Evaluation...with Final Preferences and Confidences
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of 12Z GFS/00Z ECMWF
Confidence: Average

...19Z update...

The greatest changes with the 12Z ECMWF/UKMET/CMC relate to the
southern stream shortwave crossing California on Thursday and
reaching the Great Plains on Friday. The 12Z CMC slowed down from
its previously much faster track and now lies closer to the broad
model consensus. However, the 12Z ECMWF/UKMET also sped up from
their previous 00Z cycles and there is now a faster camp led by
the 12Z ECMWF/UKMET/CMC, with the 12Z NAM/GFS lagging behind.
Given the poor run to run consistency, prefer to gently nudge
toward the newer guidance with a 12Z GFS/ECMWF blend placing the
timing toward the middle of the spread.

Elsewhere, changes were small and toward a common solution so a
general model blend is preferred across the CONUS except for the
closed low across the Pacific Northwest on Friday where a 12Z
GFS/ECMWF blend still represents an average of the ensemble means.

...previous discussion follows...

A closed low containing a mature cyclone at the surface will move
through the Northeast through Thursday morning leaving quasi-zonal
flow across the lower 48 and three notable shortwaves off of the
West Coast which will move east into late Friday.

There is good model agreement with the cyclone impacting the
Northeast today into Wednesday with a general model blend
preferred. Across the West, the northern portion of a positively
tilted upper trough, currently located from British Columbia to
offshore of the Pacific Northwest, will move east and interact
with a small closed mid-level low in Manitoba. As a surface low
organizes over the upper Midwest on Thursday, north and south
differences appear in the guidance due to differing amplification
of the closed low. A 00Z ECMWF/12Z GFS blend is in the middle of
the latest model spread and closest to the average of the latest
ensemble means.

The 00Z CMC is likely the poorest choice with systems across the
West, most notable with the southern portion of the upper trough
referenced above across British Columbia, with the CMC taking the
trough axis quicker to the east. This is in contrast to a
significant trend to be slower and nearer to the 00Z ECMWF mean.
Currently the 12z NAM and 00Z ECMWF are the farthest
offshore/slowest with the upper trough offshore, but as it moves
inland across California, only minor differences appear with
perhaps the 12Z NAM becoming a bit more amplified and slower early
Friday into the southern and central Plains. A blend of the 12Z
GFS and 00Z ECMWF lies near the middle of the latest spread and
near the preferred 00Z ECMWF mean.

A 12Z NAM/GFS and 00Z ECMWF blend is reasonable with the next,
large closed low forecast to set up over the Pacific Northwest for
Friday, with model agreement fair. However, the similar ensemble
means support a 12Z NAM/GFS and 00Z ECMWF blend over the differing
placement/timing noted in 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