Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
239 PM EDT Fri Oct 26 2018

Valid Oct 26/1200 UTC thru Oct 30/0000 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: Non-NAM blend
Confidence: Slightly above average

19z update: 12z UKMET/CMC both trended more favorably overall
toward the initial preference though adjusting closer to the
ECMWF.  This has strengthened agreement on the east coast with
both the lead coastal low as well as the clipper to shift toward a
non-NAM solution.  In the Pacific Northwest and High Northern
Plains, the ECMWF shifted a bit stronger and therefore north
slightly away from the GFS.  The UKMET/CMC continue to look more
ECMWF and even NAM like.  This would suggest a general model blend
for this system would suffice but with a lower weighting toward
the GFS with time.  So for the entirety of the CONUS a Non-NAM
blend is supported at slightly above average confidence.

Broad southern stream wave continues to progress across the OH/TN
River Valleys with surface low development up the East Coast from
Fri to early Sunday.  This wave is becoming better agreed upon
though typical biases remain in effect with each of the main
global models...which compounds toward the approaching northern
stream clipper like vort center through the upper Midwest into the
Ohio Valley Sunday into Monday.  The 12z NAM continues to be very
cold as the lead system lifts north with some fast solution
compared to the mean...leading to a flatter/northward shifted
shortwave in the Ohio Valley that is not generally preferred.  The
12z GFS, like the NAM is a bit fast but also is generally weaker
and much warmer with the clipper system, it has slowed and shifted
a bit south compared to 00z run and closer to the more consistent
ECMWF/GEFS and ECENS means.   The 00z ECMWF is a bit slow per bias
but continues to anchor the more consistent solutions while
directing the overall trends within the last 4-5 cycles (ensemble
spaghetti suite).  The 00z UKMET and CMC while on par with timing
show a sharper amplification with the lead wave and into the
development of the larger scale closed low over Southern Canada. 
This led to the approaching shortwave to likewise be a bit too
amplified compared to the bulk of ensemble members to reduce it
consideration within the blend.  As such a GFS and ECMWF blend is
preferred but the GFS's thermals continue to be well warmer than
the ECMWF so would favor more of an ECMWF or possibly supplement
some NAM thermals (due to vertical level resolution enhancement
for p-type).  With the number of moving parts (small scale
interactions) confidence in this blend is average but steadily
increasing. 

Along the west coast, as the clipper wave crosses  the Pacific
Northwest, the moisture plume returns with some subtropical
enhancement at the base of the large scale cyclone over the Gulf
of AK by Sat...this angles strong moisture transport toward the S
WA/N OR coastal range by late Sat into Sun with fairly good model
agreement in timing and orientation, eventually pressing through
the S Canadian and MT Rockies and Idaho Ranges.  Typical timing
biases manifest translating through the Rockies with the GFS/NAM
(GEFS/SREF) outpacing the CMC/ECMWF/ECENS means.  The UKMET
generally favors the slightly slower ECMWF but like the CMC looks
a bit oddly shaped with the mid-level vort/upper jet structure and
could be better represented by the ECMWF as a whole.  The 12z GFS
did slow and show greater amplification similar in vain to the
ECWMF and so there may be a better compromise brewing with this
cycle as a whole aiding some confidence.   Likewise to the East,
will favor a GFS/ECMWF blend but would weight the ECMWF a bit
higher overall.  Inclusion of the GEFS/ECENS solutions may help
stabilize some the uncertainty but would reduce the fidelity of
the sensible weather signal.   As such confidence is average in
this 12z GFS/00z ECMWF blend.  


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

Gallina