Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
236 AM EDT Thu Apr 05 2018

Valid Apr 05/0000 UTC thru Apr 08/1200 UTC

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

00Z model preferences and confidence intervals
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS initialization errors do not seem to degrade their short
range forecasts.


Weak trough/quasi-zonal flow moving into the West Saturday
Lows emerging into the Plains Saturday night/Sunday morning
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-Canadian compromise; above ave confidence

The 00z Canadian was farther south with its upper low/main bundle
of upper level energy moving into the West on Saturday than the
other guidance, though it is trending northward from its 12z run. 
With the amplitude of the flow minimizing, believe the more
northerly guidance (00z GFS, 00z NAM, 00z UKMET, and 00z ECMWF)
have a better grasp on the synoptic situation.  A compromise of
the consensus is preferred with above average confidence.


Mid-level vortex slowly dropping through Central Canada
Amplitude of the Eastern trough Saturday onward
Surface lows expected offshore the East Saturday/Sunday
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: UKMET/ECMWF/Canadian compromise; confidence no better
than ave

The 00z GFS is quicker to move energy through central Canada which
leads to a broader/quicker moving trough in the East.  This is at
odds with the other deterministic runs and available ensemble
means, so the GFS front in the western Atlantic is too fast.  Also
supporting this idea is the slowing trend seen between its 18z and
00z runs. 

The belief is that two waves of low pressure will move/exist off
the East coast with this trough, which is well represented by the
12z global ensemble guidance -- one streaking offshore the
Mid-Atlantic coast late Saturday with a second main low held up by
the amplifying trough offshore the Mid-Atlantic coast Saturday
night into Sunday.  While no model presents the best idea
independently, and the guidance has yet to settle down, a
compromise of the 00z UKMET, 00z ECMWF, and 00z Canadian should be
in the ballpark.  The ensemble means are finally more
agreeable/converging with their surface solution, which brings
hope that future runs would show better agreement and less spread.
 Confidence is no better than average in this solution due to the
larger than average deterministic spread at this time range and
instability of the guidance.


Disturbance moving by Michigan late Thursday/Friday
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-UKMET compromise; above average confidence

The 00z UKMET appears too narrow with this mid-level disturbance
as the general flow pattern in the northern stream is one off
lesser amplitude, though it has trended slightly broader from its
12z run.  This difference aloft appears to distort the appearance
of the UKMET's trailing surface high.  Believe a broader shortwave
makes more sense, which also befits the 00z GEFS/12z ECMWF
ensemble mean solutions.  A compromise of the 00z NAM, 00z GFS,
00z Canadian, and 00z ECMWF is preferred with above average
confidence.


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

Roth