Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
228 PM EDT Tue Jul 10 2018

Valid Jul 10/1200 UTC thru Jul 14/0000 UTC

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

12Z model evaluation including preference and forecast confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Model Analysis for the CONUS...

Overall Preference: Non-UKMET blend
General Confidence: Slightly above average

19z update: The 12z UKMET continues to be fast progressing the
frontal zone through the northern tier of the US/Great Lakes and
eventually weakens the inner core of the upper low shifting toward
more zonal flow along the US/Canada boarder a bit earlier than the
remaining guidance.  Small run to run variations have occurred
with the ECMWF/CMC but have further tightened the overall forecast
mass fields throughout the CONUS/forecast time frame...enough to
support a non-UKMET blend. 


PRIOR DISCUSSION
~~~~~~~~~~~~~~~~~
As Tropical Storm Chris lifts northeast, shortwave energy
over-topping the larger scale ridge in the central US will descend
and amplify/sharpen the east coast trof early Thurs into Fri. 
There are moderate timing differences in the ensemble and
deterministic guidance...the 00z UKMET is fast and the 12z NAM is
slow.  Eventually, as the wave sharpens some guidance suggests a
weak closed low feature near SE Canada/Maine.   The 00z UKMET/CMC
were a bit further south with the core of the vort center and
carve out a deeper trof compared to the ECMWF/GFS and NAM as well
as the GEFS/ECENS means.  This is overall the largest model
difference through the CONUS overall and would favor excluding the
UKMET/CMC toward late Thurs/Fri for this region.  

The Northwest US trof will continue to lift northeast into SW
Canada today further deepening to a closed low...the UKMET is a
bit deeper, earlier and leads to some faster progression of the
cold front through the Great Lakes by Fri/Sat, with some
flattening (W-E) of the orientation of the front  Fri compared to
the remaining guidance, including the bulk of ensemble members. 
Otherwise there is solid agreement for this system as well
including the eventual capture of the compact vort center that
reaches a weakness in the ridge over CO, Thurs into Fri. 

As such a non-UKMET blend is supported across the CONUS, with
reduced CMC influence along the East Coast/Western Atlantic toward
end of the week/early weekend.


...Tropical Storm Chris off the East Coast...

Preference: 12z GFS/ECMWF is closest to 15Z NHC advisory

Please see the latest NHC products for the official forecast,
reasoning, and model track and intensity preferences for Tropical
Storm Chris.

19z update: The 12z ECMWF shifted faster and remains along 15z NHC
forecast track but is still slower than the official forecast
overall.   The UKMET remains well timed, but also continues to
veer left of track toward NE Nova Scotia relative to the other
guidance.  The 12z CMC like the ECMWF also trended faster but
remains slower than the ECMWF making the ECMWF a better
combination with the GFS to proxy the official 15z NHC forecast.

Prior Discussion
~~~~~~~~~~~~~~~~~~
As Chris accelerates up the East Coast (offshore) nearing Cape
Race by Fri...there is moderate model spread with the 12z GFS
shifting east and now tracks along the NHC official forecast and
the NAM (right) both fast relative to the official track.  The 00z
UKMET has good timing relative to the forecast but is well left of
track.  The ECMWF/CMC show the orientation to the 15z NHC track
but are much slower than the official forecast.  As such there are
no good deterministic/ensemble means that represent the track
ideally, and so a blend of the 12z GFS for the fast guidance and
50% ECMWF for the slow guidance will likely be a best proxy to the
official forecast.

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

Gallina