Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
139 AM EST Sat Dec 22 2018

Valid Dec 22/0000 UTC thru Dec 25/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend, weighting increasingly to
            00Z ECMWF/CMC/UKMET/12z ECENS mean for West Coast
after 24/00z
Confidence: Above average with exception to the West Coast
             after 24/00z which is average.

07z update: Small adjustment by the late deterministic solutions
suggest tighter overall agreement in timing and general strength
of wave entering OR/CA by late Monday into Tues.  The UKMET
trended faster and perhaps a bit larger with the developing closed
low, but the CMC trended slower but also a shade north of the
growing consensus...this while the ECMWF shifted ever so slightly
south but also a bit less compact/strong relative to the 12z run. 
As stated before, the NAM/GFS appear a bit fast/weak comparatively
and still may be behind the trend.  While a general model blend
may suffice, ensemble suite/recent shifts, suggests shifting away
from the GFS/NAM after 24/00z.   As such will favor a shift toward
heavier ECMWF/UKMET/CMC weighting along the West coast into the
Southwest.

---Prior Discussion---
Models have consolidated on common synoptic pattern and forecast
particularly across the Eastern two-thirds of the CONUS.  This
leaves the greatest model differences/uncertainty related to
precise strength and timing of shortwave/jet energy entering the
Pacific Northwest at the beginning of next week.  Lead
height-falls and strong surface wave slides north of Vancouver
Island early Sunday with strong model agreement, it is the
upstream wave(s) that show greatest difference.  The 00z NAM and
GFS both remain a bit early compared to the remaining guidance,
with the NAM a bit stronger with a weaker surface wave reaching SW
OR/N CA by midday Monday.  The GFS remains weaker, but also
trended much slower and therefore, the jet energy helps to dig the
trof into CA by Tuesday, more favorably and closer to the 18z
FV3-GFS which was initially more favored than the 18z GFS.

The slower and therefore much stronger, amplified solutions
anchored by the 12z ECMWF support strong surface cyclones by late
Monday into the same region.  The 12z ECWMF appears a bit
over-amplified with the closed low compared to many other ECENS
members and even lags a deep/compact CMC.  The 12z UKMET is
uncharacteristically the slowest and therefore the most
compact/deepest closed low feature by 12z Tuesday.   While the
trends are toward the deeper/compact solution, the UKMET appears a
bit too aggressive, like the opposite in the 00z GFS solution. 
Still a general model blend seems appropriate here, for the late
forecast time period, but at least the volatile synoptic pattern
and run to run variation appears to be settling down enough to
have average confidence in this general model blend (weighted
toward ECMWF/CMC).


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

Gallina