Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
243 AM EDT Thu Oct 31 2019

Valid Oct 31/0000 UTC thru Nov 03/1200 UTC

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

00Z Model Evaluation with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Central to Eastern U.S. storm through Friday
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-NAM blend
Confidence: Above average

07z update: The 00z CMC shifted into better overall agreement with
the GFS and there was solid continuity within the UKMET/ECMWF new
runs to suggest a non-NAM blend (still a bit too slow/deeper,
relative to the suite) as preference at above average confidence.

---Prior Discussion---
The environmental pieces are coming together toward the fairly
rapid development of a strong surface cyclone in the Ohio Valley
sliding into the St. Lawrence Valley toward Fri with a strong,
progressive cold front pressing across the Eastern US.  The
overall guidance, while there are some small internal differences
particularly after 36hrs (CMC is north, and the 12z NAM is
slower), the agreement in the 00z GFS and 12z ECMWF/UKMET with
prior runs provides above average confidence in a GFS/ECMWF and
UKMET blend.

Next upper shortwave, press of cold air behind front over the
Plains/Midwest by this weekend
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-NAM blend
Confidence: Above average

07z update: The 00z UKMET trended a bit better, and given the 12z
run was nearly included in the preference, this shift is
sufficient to support a Non-NAM blend at above average confidence
for this system as well.

---Prior Discussion---
A northwest flow regime sets up across Canada, allowing for
another shot of cold air to press into the Northern
Plains/Boundary Waters region, supporting a surface wave and
frontal boundary clipping the Great Lakes by late Sat into Sunday.
 The 00z NAM, likely being a bit colder with its known bias, digs
a bit further south and is a bit stronger/deeper south with the
trof through the Ohio and Tennessee Valley by Sunday.  Similarly
the UKMET is deep in the upper TN valley/S Appalachians, though
this is better mass agreement with the GFS/ECMWF/CMC than the NAM;
this is a bit outside of the ensemble suite but could potentially
be added at lower weighting in a blend, if so desired.  However,
will favor a 00z GFS and 12z CMC/ECMWF blend at above average
confidence.

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

Gallina