Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
133 AM EST Wed Dec 26 2018

Valid Dec 26/0000 UTC thru Dec 29/1200 UTC

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

00z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend (non-NAM Sat)
Confidence: Slightly above average

07z update: With a slight speeding up/quicker weakening in the 00z
ECMWF and more substantially in the 00z CMC, believe a general
model blend would suffice for the initial cyclone/trof.  
Likewise, the 00z UKMET/CMC and ECMWF trended toward the 00z
GFS/GEFS solution with the second wave, while the 00z NAM is
slightly faster and stronger (though flat) crossing into the
Central Plains by Sat, it is a sufficient departure to suggest it
removal, but given the reduction of overall spread confidence is
increased to slightly above average for the entire forecast period
in a general model blend transitioning to non-NAM blend for second
Southwest trof.

---Prior Discussion---
Elongated neutral trof is bottoming out across the desert
Southwest at the start of the period with height-falls already
recharging the Southern Plains with moisture and instability with
the development of classic Plains cyclone today through Friday
lifting into the Midwest before shearing into confluent flow
aloft.  Here, the guidance continues to be consistent with
difference in guidance in typical traditional biases; ie. GFS
slightly faster, ECMWF/CMC a bit too slow/compact hanging onto the
trof a bit too long...but still not too bad.   Subtle upstream
shortwave/jet streak quick on the heals mainly in the southern
stream, may spark a weak wave along the cold front through the
South.  The 00z GFS trended a bit weaker and now is pressing the
heavies QPF/convection along or just east of the spine of the
Appalachians in line with the 00z NAM/12z ECMWF/18z FV3 GFS.  As
such a non-CMC solution appears to work for this system as a whole
from Plains through the East by early Sat

Now, the slower CMC/ECMWF solutions actually support a narrowing
of the wave length spacing with the upstream kicker wave, this has
been steady trend noticed in the cycle to cycle ensemble spaghetti
analysis, though the CMC is much too strong on both features
eventually leading to a strong closed low across AZ/NM by the end
of the forecast period, away from the ensemble trend.  Likewise,
the UKMET is very deep/compact with the upstream development and
due to this is very slow/west in the guidance suite.   The 00z
NAM, does not appear too bad...though is a bit fast bringing out
the jet/vort energy stretching it across the Central Plains by 12z
Sat, with minimal sensible weather difference.  Here the 18z FV3
GFS trend has been against the ensemble suite and closer to the
CMC, while the operational 00z GFS is more in line with the
ECWMF/00z ECENS mean.  As such will favor the 00z GFS and 12z
ECMWF for the upstream wave at average confidence. 

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

Gallina