Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
239 AM EDT Sun Oct 06 2019

Valid Oct 06/0000 UTC thru Oct 09/1200 UTC

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

00Z Model Evaluation with Preferences and Forecast Confidence
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...Overall Pattern Across the CONUS...
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Preference: General model blend...Western 2/3rds of CONUS
   12z ECMWF/UKMET and 00z NAM (some GEFS...Eastern CONUS
Confidence: Slightly above average
   Average in Eastern CONUS after 09.00z

19z update: The 00z ECMWF trended a bit weaker and therefore a bit
faster lifting the lingering shortwave energy out of the Upper
TN/OH Valley, leaving the focus for surface cyclogenesis further
east like the prior run and initial preference and close to the
00z NAM. The 00z UKMET, shifted ever so much closer to the
NAM/ECMWF while the CMC trended stronger and very closely packed
to the GFS.  The 00z GEFS continues to depict a split in the
solutions, half toward the operational GFS and a few clustered
toward the NAM/ECMWF/UKMET... still suggesting the NAM/ECMWF/UKMET
blend is still favored over this slower, more amplified E TN/OH
Valley solution with stronger warm conveyor belt pumping moisture
back across the Mid-Atlantic.  This will keep with initial
preference and confidence still at average.

Elsewhere, confidence remains slightly above average in a general
model blend.


---Prior Discussion---
The northern stream flow pattern  will support a strong upper jet
progressing the lingering positive tilt trough energy across the
eastern third of the CONUS, with eventually strong cold pool
dropping south out of Arctic Canada to enhance trough development
in the Northwest/Northern Rockies by Tuesday and digging into the
Snake River/N Great Basin by the end of the short-range forecast
period.  Additionally, a tropical wave will approach the Bahamas
and amplify in front of the advancing eastern trough, with large
model variation in strength/placement/evolution of a Gulf Stream
surface wave and any remaining shortwave energy at the tail end of
the northern stream trof through the Cumberland Plateau into the
Central Appalachians.

As for the lead shortwave, the trend as been a bit faster overall
in the ensemble suite/guidance, with the 12z ECMWF and bulk of
members along with the UKMET and 00z NAM progressing the frontal
zone through the upper TN/OH valleys and across the
Mid-Atlantic/Northeast.  Interestingly, the GFS has trended away
from this evolution, supporting a slower, more amplified wave in
the Cumberland Plateau by Tuesday.  This is mostly due to a
stronger, faster northern stream jet initially, typical of a
negative bias.  This in turn, severs the connection to the tail
end of the trof, which minus the very slow CMC is fairly alone,
even within the 18z GEFS member solutions.   Additionally, this
stronger cyclone and flatter surface front along the
Mid-Atlantic/south of New England helps with the tropical wave
lifting north and draws a stronger easterly flow jet north of the
boundary and stronger warm conveyor, to advect more
moisture/instability across the boundary and appears less
favorable even in the CMC which is slow.  As such will favor a 12z
ECMWF/UKMET and 00z NAM blend for the eastern US particularly
after 09.00z.  Given inconsistency in the guidance trends away
from each other and the importance of small timing/intensity
differences, confidence is average in the blend, particularly for
day 3 when the tropically originating wave lifts up the east
coast.

In the west, the guidance is much more agreeable, with the
timing/orientation and strength of the digging trof.  The 00z NAM
may be a bit off, given typical day 3 negative bias of being a bit
stronger; allowing a stronger northeast shortwave out of the
Northern US Rockies into SE Canadian Prairies late Tuesday,
relative to the other guidance including ECENS and GEFS ensemble
suites.  Still, this is fairly small differences that its
inclusion to a blend is fair, but perhaps at lower weighting. 
Though, the 00z NAM and GFS may be a bit more favorable about the
subtle subtropical stream shortwave that slides into the Southern
Plains in advance of the trof.  Both are a bit more amplified and
support a bit northward shift in light to moderate QPF
development.  Confidence is average in this general model blend.


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

Gallina