Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
150 AM EST Sat Dec 15 2018

Valid Dec 15/0000 UTC thru Dec 18/1200 UTC

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

00Z Model Evaluation...with Final Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: General Model Blend
Confidence: Above Average

07z Update: The 0z CMC has trended towards the better model
clustering, and thus no longer appears to be as significant an
outlier over the east. The 0z ECMWF has trended stronger with the
vort energy as it moves off the east coast, resulting in a
stronger low a bit closer to the coast off Maine. The NAM is
closer to this EC camp, with the GFS/CMC/UKMET remaining
weaker/east. Overall these differences still appear to be within
the normal error for the lead time, and a multi model consensus
should still be a good option for now.

Previous Discussion...

An amplified upper level pattern over the lower 48 will feature
general troughing in the eastern U.S. with a combination of
shortwaves to impact the East Coast. A trio of mid-upper level
waves will impact the western U.S. through Monday, the first of
which is quickly moving east across the northern Rockies this
morning, followed by a progressive trough and moisture plume
Sunday night, and a third, longer duration, atmospheric river
directed into the Pacific Northwest by Monday night.

Overall models are in above average agreement with both the
eastern and western U.S. systems. The closed low over the east
will continue to track northeast, with a surface low developing
off the Mid Atlantic coast Sunday. This area of low pressure will
gradually intensify as it moves to off the MA coast Sunday night,
with a more rapid development of the low expected through Monday
off of Nova Scotia, as northern stream energy dives southeastward
reinforcing the low. Forecasting low development/track in these
scenarios is always tricky, and likely to see some model
fluctuations over the coming days. With that said, the current
suite of guidance is generally in very good agreement on the
synoptics and track/intensity of this low...with differences
mainly within the noise expected at this lead time. The 12z CMC is
probably the biggest outlier, having the least amount of phasing
of the energy, and thus also the weakest and furthest east with
the low. Thus would probably continue to stay away from that
solution, but otherwise a multi model blend of the
GFS,NAM,ECMWF,UKMET should suffice.

Out west, also see above average agreement, and thus a multi model
blend should be good there as well.


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

Chenard