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Model Diagnostics Discussion
(Latest Discussion - Issued 0633Z Dec 10, 2019)
Version Selection
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Abbreviations and acronyms used in this product
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
133 AM EST Tue Dec 10 2019

Valid Dec 10/0000 UTC thru Dec 13/1200 UTC

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

00Z Model Evaluation with Preferences and Forecast Confidence

...Eastern CONUS...
Preference: General model blend
Confidence: Slightly above average

07z update: The 00z UKMET weakened the influence of the greater
convective/slantwise instability activity across the Piedmont Wed
morning that enhanced the jet a tad...this placed the mass fields
more in line with the remaining guidance.   Small mesoscale
differences in dry/moist advection remain and still be needed to
be ironed out, but synoptically in mass fields/frontal timing; a
general model blend can be afforded.

---Prior Discussion---
The model guidance mass fields continue to tighten with the
northern stream large scale cyclone and associated deep surface
low in the Great Lakes currently.  The attendant cold front is
also well timed and placed through the mid-week including the very
strong jet.  Smaller scale, dry slot/moisture ribbons continue to
come into tighter agreement as well but the 12z UKMET has a wet
bias currently with this system and it looks it again along the
East Coast/Piedmont region that feeds a bit upscale to the jet
holding the trailing inflection/right entrance a bit to make it a
bit less favorable.  Other-wise the 00z GFS/NAM and 12z ECMWF
continue to be very tight overall. 

Additionally, the Arctic shortwave/kicker is timed and shaped well
to have increased confidence in the overall evolution through to
end of week in the East.  Confidence in a 00z GFS/NAM and 12z
ECMWF Blend is slightly above average.

...Western to central CONUS (Gulf Coast Day 3)...
Preference: 00z GEFS/ECMWF and 12z ECENS blend
Confidence: Average

07z update: The 00z ECMWF trended a tad slower and therefore a bit
further south in the southern stream, this was bolstered by a
consistency in the 00z GEFS with the 18z GEFS, and away from the
weaker/faster 00z GFS, to retain confidence in the ECMWF/ensemble
initial preference.  However, the southward trend does at least
call into question the 00z NAM that is a bit more compact
(slightly faster) that leads to a northward pull of Gulf
moisture/ perhaps a bit less influence that initially
thinking is warranted.  The UKMET held serve, but the 00z CMC
trended toward the GFS/UKMET side of the suite at the end of the
forecast period (favoring stronger northern stream forcing),
deflating some of the gained confidence from the GEFS.  So a 00z
GEFS/ECMWF and 12z ECENS mean blend is preferred at average

---Prior Discussion---
In the wake of the large Vortex that has dominated the Northeast
portion of the continent, enhanced ridging exists along the West
Coast, with an approaching southeast shortwave trof extension of a
larger Alaskan closed low into the Pacific Northwest to N
California by late Tuesday.  This wave continues to
stretch/elongate through the ridging helping to split the
shortwave energy into a northern stream packet through the
borderland Rockies as well a southern portion of the wave entering
the Great Basin.  The GFS has been trending best with the
evolution of this situation with a stronger reflection in the
southern stream while the northern wave keeps pace with weak
phasing.  Only the 12z UKMET is out of tolerance through the
Rockies, still favoring a stronger northern stream which leads to
a faster evolution and surge of the jet across the Central MS
River valley toward the end of the forecast period... which
deflates the subtropical shortwave lifting north and squashes the
development of Gulf Coast system at the end of Day 3.  Obviously,
the UKMET is not favored in the evolution.  With the 12z
ECMWF/ECENS trending toward the GFS/GEFS evolution there was
growing confidence.  However, the 00z GFS shifted toward a weaker
solution and starting looking more like the UKMET, becoming very
weak and fast by the end of Day 3.  While reducing confidence,
hoping this is a one-off solution given its break from growing
ensemble congruence.  So will favor a 00z NAM/18z GEFS and 12z
ECMWF/ECENS mean solution at average confidence. 

Model trends at
500 mb forecasts at