Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1202 PM EDT Sat Nov 03 2018

Valid Nov 03/1200 UTC thru Nov 07/0000 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: Blend of the 12z GFS/ECMWF/UKMET
Confidence: Slightly Above Average

Through the short-range, there are three major components/waves
internal to the larger scale global trof that continues to
dominate the central portion of the continent through this period.
  The first is the current mid range amplitude wave that is taking
shape out of the central Rockies into the Central Plains today,
the second and third are of similar source currently in the Gulf
of Alaska and expected to shear into strong jet streak/quasi-zonal
(WNW to NW flow) crossing the Western Coastal Ranges later today
into Sunday with the northern portion becoming the fulcrum pivot
of the larger scale trof along the US/Canadian boarder Mon/Tues
and the strong jet digging a negative tilt trof through the
Southern Plains into the Lower Arkansas River Valley by Tues.  
The evolution of one affects the others, and the catalyst for
model spread appears to be contingent on the placement/depth and
orientation of the lower tropospheric cold air. 

The 12z NAM, typical of bias, has a very cold solution however,
holding back the vast depth closer to the fulcrum pivot wave,
enhancing it; this leads to a slightly weaker initial wave through
the Great Lakes allowing for the base of the trof/nose of the jet
to be less sharp/broader and therefore leaning forward.  At end of
all, this elongates the second surface low and frontal zone Monday
to Tuesday through the Plains into the Great Lakes.  This is not
favored and is outright rejected from WPC preference.   
Similarly, but not to the magnitude of difference with the overall
suite, the 00z UKMET has a different evolution to the cold air, it
does not retain it along the US/Canada border but it is a bit
tighter in gradient to the developing closed low and therefore
supports a very deep surface low from IL into Lake Michigan,
angling much further west to the ensemble spaghetti low plot. 

The remaining guidance is quite similar and appear to handle a
more sensible cold air/baroclinic cyclogenesis with both waves, in
particular the second wave Mon/Tues.  The 12z GFS trends show the
continuity with the 00z/06z runs as well as the 00z ECMWF/CMC runs
to have slightly above average confidence overall in a 12z GFS and
00z ECMWF/CMC blend.

Of note in the Southeast/QPF: The 12z GFS and other GFS/NCEP suite
guidance continue to show reduced phasing with energy rotating
northeast into confluence out of the Southeastern Atlantic toward
the Gulf Stream, so it remains pressed further southeast.  On the
other hand, the ECMWF has been the most aggressive with this
phasing drawing the frontal zone more ashore... the 00z ECMWF run
has become more sensible keeping the boundary near the SC/NC
coast, but also shows very high feedback from latent heat release
supporting a weak surface wave toward the mouth of the Chesapeake.
 Here the UKMET/CMC appear more sensible than either the
GFS/ECWMF...so please see WPC QPF grids for additional details.   


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

Gallina