Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1218 AM EDT Fri Apr 06 2018

Valid Apr 06/0000 UTC thru Apr 09/1200 UTC

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

00Z GFS/NAM evaluation with preliminary model preferences
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS initialization errors do not seem to degrade their short
range forecasts.


Trough moving through West into the Plains/Great Lakes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: GFS/ECMWF/UKMET blend; slightly above ave confidence

The 12z Canadian was faster with its depiction of this system when
compared to the other guidance, while the 00z NAM was the slowest.
 The 12z ECMWF, 12z UKMET, and 00z GFS are reasonably close to the
12z ECMWF/18z GEFS ensemble mean solutions to be considered
useful.  To deal with the uncertainty, a compromise of these three
is preferred with slightly above average confidence.


Trough moving through the East
Low moving through the Southeast/Western Atlantic
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: GFS/NAM/ECMWF blend; confidence slightly above ave

With the first shortwave moving through the Great Lakes/Northeast
Friday into Saturday, differences are minimal.  The 12z Canadian
was the quickest with the overall trough progression, mainly due
to its quicker trough progression upstream across the
Plains/Midwest.  Whether or not a pair of shortwaves moving
through the trough phase in a couple days is also an issue amongst
the guidance, with the 12z UKMET the least phased and more
westerly with its surface low solution offshore the East coast. 
Because of its solution aloft, the Canadian is the most eastward. 
While delaying the phasing of shortwaves within a trough is
normally not a bad play, the 12z UKMET was on the southwest fringe
of the 12z global ensemble guidance.  A compromise of the 00z NAM,
00z GFS, and 12z ECMWF appears best here, and a compromise of
their mass fields is preferred.  For preferences regarding the
quantitative precipitation forecast (QPF), consult the WPC suite
of precipitation-related products, including the QPF discussion,
for more details.


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

Roth