Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
144 PM EST Tue Jan 08 2019

Valid Jan 08/1200 UTC thru Jan 12/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: 12z GFS and *11/00z* ECMWF blend
Confidence: Slightly above average

19z update: The 12z UKMET resolved the over amplification through
the Gulf of Maine with the east coast system, so even tighter
overall agreement now exists with this system, supporting a
general model blend or non-NAM solution.

Further west, the spread continues to be modest with, though it
does appear more energy is undercutting the split flow/ridge in
the Intermountain west, to develop into a solid yet broad trof
over NM/Southern Plains through Friday evening.  Here, even the
12z UKMET shows similar evolution, but remains on the very strong
side, nearly 60dm deeper at 5H and 30dm at 7H, leading strong,
more northerly QPF/moisture flux and therefore remains on the
outside of preference.  The CMC continues to have the strongest
ridge upstream, sharpening the trof a bit too much in the Southern
High Plains.  The 12z ECMWF trended a bit weaker, and therefore
was slightly slower moving through the southern stream, but still
matches the GFS/NAM well enough to keep a GFS/ECMWF/NAM preference
across this region.

However, this slowing, leads to further upstream issues and now
the ECMWF has shifted to the faster side of the ensemble suite and
is now well north of the 00z solution,12z GFS, i.e. initial
preference.  This may be a further transition, but this would also
lead to a significant departure from continuity.  The 12z UKMET
shows similarity to the GFS and 00z ECMWF continuing some
continuity/preference there.  While not ideal, will support a 12z
GFS/UKMET and 00z ECMWF blend preference here.   Across the CONUS,
a 12z GFS and 00z ECMWF solution will remain the WPC preference. 
Confidence is reduced to average given the less preferable 12z
ECMWF solution in the West, increasing the overall spread.


---Prior discussion---
Model guidance appears to have settled on solid agreement with the
deepening broad cyclone along the Northeast.  Obviously, there
remain subtle but potentially significant differences, such as the
typically cold NAM continuing this trend (though also has better
vertical layer differences to aid in p-type choices), or the 00z
UKMET suggesting a small scale increased diffluence region that
aligns over the Gulf of Maine, spurring a very deep surface low
compared to the remaining guidance. As such would favor a
GFS/ECMWF/CMC blend for mass/thermal fields for this system.

The guidance uncertainty resides in the break down of the deep
closed low off the West coast, into split flow and the resultant
emergence of in the lee of the Central Rockies and southern Plains
by day 3.  The 12z GFS trended favorably toward the ensemble trend
and press the shortwave at the base of the larger scale trof south
through the split flow and interacting with the shortwave in the
sub-tropical stream across the Southern Plains by Friday evening. 
This is similar to the 00z UKMET, but the UKMET is stronger and
faster and given better agreement elsewhere will avoid its
inclusion at this time.  The 12z NAM also trended better, and
while may be a bit stronger in the northern stream/Northern
Plains, it is more favorable further south to have some inclusion
there, but less further north.  The CMC continues to but fast and
most amplified with the Intermountain west ridging, even as the
ensemble trend backs down on this amplification.    As such a 12z
GFS/00 ECMWF blend is preferred though some inclusion of the 12z
NAM may be ok in the southern stream and less so north.

This shift faster also increases a bit of upstream ridging in the
Pacific in advance of the next system, and so has also slowed the
GFS closing off low off the SW Coast of California as the 06z run
did.  And while it is a bit faster than than the ECMWF (and
therefore a bit north with the surface low), this is a favorable
agreement with the ECMWF.  The 12z NAM still is stronger/more
closed developing a deeper, further south surface inflection.  The
CMC is most out of phase leading to a narrower, more strung out
trof with a much faster surface low advancing to the coast by 00z
Sat.  While the UKMET has a very strong/deep surface low, its
shape, timing of the trof as a whole shows some benefit and
potentially be included at lower weighting for this system; but as
a whole across the CONUS a 12z GFS/00z ECMWF blend is WPC
preference.  Confidence is slightly above average in this blend, 
a bit higher eastward and lesser so in the Intermountain
West/southern plains by Fri.

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

Gallina