Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
147 AM EST Mon Dec 24 2018

Valid Dec 24/0000 UTC thru Dec 27/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-GFS blend (use FV3-GFS in blend instead)
Confidence: Slightly above average

07z update:  The 00z ECMWF trended a bit faster under a slightly
faster upstream kicker wave, placing it a bit more favorably
overall within the ensemble suite.  Interestingly, this matches
better with the FV3-GFS over the operational 00z GFS.  The 00z CMC
continues to trend faster and now appear to be
uncharacteristically faster, especially with the dry slot but
still quite good overall for inclusion.  The UKMET also favorably
shifted to a more concentric closed low feature ejecting out of
the Southwest and while it may be a bit heavier QPF (per bias), it
seems a solid inclusion at this point.  This places the 00z
operational GFS on the outer fringe of the growing consensus and
would favor blending the FV3 instead.   This appears true for the
upstream kicker wave/jet streak.  As such a non-operational GFS
blend is preferred but still weighting heaviest to the 00z ECMWF
at increased confidence (slightly above average). 


---Prior Discussion---
GOES-16 WV suite depicts a few small compact shortwaves across the
Great Lakes and Central Allegheny Plateau into PA/S New England,
becoming broadly zonal across the US today into Tuesday.  A subtle
wave entering the Northwest currently, slides quickly through the
Rockies and amplifies slightly across KS/MO with some weak model
spread, with the CMC a bit north, and GFS a bit drier than the
ECMWF/NAM/UKMET, but still overall strong agreement for high
confidence general model blend.

A strong Pacific wave starts to sharpen at the OR/CA border late
today into Tuesday with a fairly agreed upon surface reflection
and this agreement generally (obvious mesoscale/storm scale
over/under internal wave growth) continues through much of Tuesday
at the trof bottoms out in AZ.   After this point, the model
spread increases due to slight differences in shape/maturity of
the deep cyclone, as well as placement of upstream shortwave
energy at the southeast periphery of Gulf of AK closed low. 
Typical of bias, the GFS is a bit fast with the upstream wave
supporting a slightly faster kick and helps to elongate and
support weak negative tilting and lifts the surface wave out
northeast south and east of the main ensemble cluster but fairly
consistent with prior runs.  Opposite of this is the slowest,
least amplified kicker wave in the 12z ECWMF allowing for the most
concentric closed low to lift out of the southwest into the
Plains.  As such the GFS has very limited strength to the
deformation zone in the Plains, shifting focus to IA/MO...as well
as faster eastward advancement of the convection/front across the
Southern Plains, while the ECWMF, is stronger in the deformation,
which seems a bit more logical given the cold air placement along
the lee of the CO Rockies.  The 00z NAM and 12z CMC are between
the two solutions, though the CMC is uncharacteristically faster
with the upstream wave but also is a bit more concentric than the
00z GFS lifting north, and appears quite useful in the blend for
this lead/closed low, but less so with the upstream kicker wave
being too fast/deep.  The 00z NAM has excellent central mass
fields through its depth, but also shows much greater dry air
throughout the forecast with the dry conveyor belt/slot surging
across the Plains by early Thurs and is not particularly favored
with respect to QPF, but ok in mass fields).  The 12z UKMET like
recent days runs has quite strong, deep features comparatively
speaking and shows greater/faster negative tilt orientation than
the GFS and is the outlier to the ensemble solutions.   As such a
non-UKMET blend is supported at average confidence (above average
before 26/00z), though will be hedging blend/preference toward the
ECMWF/CMC late Wed into Thursday in blend weighting. 

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

Gallina