Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1230 AM EDT Fri Apr 05 2019

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

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

00Z Model Evaluation with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Shortwave/surface low crossing the Ohio Valley Fri/East Coast
Sat...
...Potential surface low developing along the Southeast coast Fri
night...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Slightly above average

Both the 00z NAM/GFS are a bit more amplified across the Ohio
River Valley, directly sampling the current observations.  This
does not significantly affect later evolution of the wave and
surface low along the Southeast Coast later tonight.  As such a
general model blend can be employed at slightly above average
confidence.

Model solutions are reasonably well-clustered with respect to this
system through Fri as the shortwave and weak surface low move into
the Ohio Valley. Solutions have come more toward the idea shown
yesterday by a number of ECENS/CMCE members that another surface
low should develop along the Southeast/southern Mid-Atlantic coast
by Fri night/early Sat, with the NAM/GFS now also showing a weak
wave of low pressure moving northeast off the Mid-Atlantic coast
through Sat.


...Active Pacific upper-level jet reaching the West Coast with
series of embedded shortwaves...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Average

Models continue to show larger scale consistency with
placement/timing of the deep closed low across the NE Gulf of
Alaska.  Models also show fairly good agreement in the multiple
outer bands/shortwave troughs quickly rotating through the
Northwest Pacific states, while run to run consistency in precise
depth of each wave continues to be eluded, the timing is suffice
to have confidence overall.  QPF-wise, the intersection of the
base of each trof and the deep moisture stream provide higher
confidence in the placement of the highest moisture flux across S
OR/N CA.  As such, a general model blend is preferred, mostly to
tamp out some of the most amplified waves (ie, 00z GFS early Sat,
or 00z NAM/12z UKMET early Sunday), but keep the strong moisture
flux and focus.  However, this would reduced confidence in any
specific wave, though fairly high in the overall pattern; so
average overall.


...Southern stream shortwave crossing the Southwest Fri and
reaching the central U.S. Sun/Mon...
...Connection to northern stream wave entering Southern Prairies
into Northern Plains by early Mon...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 00z GFS/12z ECMWF blend
Confidence: Slightly below average

At the start of the period, an ill-defined base of shortwave
energy crosses through the Southwest, amplifying/stretching
(vertically) slightly after crossing into the Plains on Sat,
additional southern peripheral shortwave energy from the energetic
Pacific, reinforce and broaden the southern trough by Sunday. 
Strong jet crossing from the atmospheric river into the Northern
Rockies, will aid the left rotor to the jet circulation across the
Southern Prairies by Sunday as well, leading to two cyclones north
and south, respectfully of the strong SSW flat jet. 
Interestingly, the 00z NAM is broader with the 250mb jet, and
retards the westward progression of the deformation zone between
the cyclones relative to the GFS/ECMWF.  While the 00z GFS did
strengthen the northern stream and shift the jet axis slightly
north it did not affect the overall evolution too much relative to
the 18z run or 12z ECMWF solution.  It does, delay the southern
stream solution and help support a more rounded cyclone through
the southern Red River Valley.   This trends away from the 12z CMC
which has been a bit faster than the GFS/ECMWF in the southern
stream, but also significantly amplifies the northern rotor
cyclone across Ontario by 84hrs.   The UKMET is and has been out
of phase with the ensemble suite.   Overall, this is a very low
predictability pattern, given the importance of many weak
shortwave trough placement relative to each other, as well as
influence of Pacific jet orientation.  This leads to lower
confidence overall in any particular blend.  Still, will favor a
blend of the GFS/ECMWF at slightly below average confidence.


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

Gallina