Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
235 PM EDT Fri Aug 14 2020

Valid Aug 14/1200 UTC thru Aug 18/0000 UTC

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

12Z Model Evaluation Including Preferences and Forecast Confidence

...Long wave trough moving from Northern Plains into Great Lakes
Sun/Mon and through to Interior Northeast Mon/Tues...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend through 17.00z
            Non-NAM thereafter      
Confidence: Slightly above average

19z update:  The 12z ECMWF/UKMET/CMC all trended a bit further
south with the developing wave within the elongated trof (much
like the NAM/GFS).  This increases the overall agreement though
the NAM still has a depth/strength concern for inclusion in the
blend.  As such will keep with initial preference of general model
blend transitioning to Non-NAM blend after 17.00z.  Confidence
continues to increase but still in the the realm of slightly above
average.

---Prior Discussion---
Strong shortwave crossing the Northern High Plains will take the
strong surface wave through the Red River Valley into Canada with
very strong agreement, the model spread starts to increase with
the upstream 'kicker' shortwave and associated jet streak that
will help to elongate the larger scale trough more negative tilted
through the Great lakes into Sunday.  The UKMET/CMC/ECMWF are all
very elongated having retained the main inner core to the large
scale closed low over N Canada much further north.  The GFS/NAM
suggest a secondary compact 5 vorticity center much further south
along the trof axis into NE Ontario by late Monday.  This will
drive height-falls dynamic forcing into New York and the Interior
Northeast in greater strength, particular the NAM.  Given the NAM
tends to over play this by the end of Day 3, there is less
confidence in its utility after 17.00z.   As such, a general model
blend is preferred with a non-NAM blend (mainly in mass fields)
after 17.00z.  Confidence is increasing to slightly above average
given similar sensible weather evolution even with moderate mass
field spread.  

...Ill-formed long wave trough across OH/TN Valley slowly exiting
Carolinas by Mon...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-UKMET blend
Confidence: Average

19z update: The 12z UKMET continues to be much weaker and
therefore flatter with the deeper cyclonic pattern through the
Southeast, including the surface wave as the start of the
workweek.  The ECMWF trended a tad faster brings it closer to the
overall cluster and along with the NAM and 12z CMC show the deeper
GFS a bit further north and east overall.  That is minor enough to
suggest a Non-UKMET blend through the forecast period and given
increasing agreement (but still with weak flow and convective
feedback) confidence is increased to average.

---Prior Discussion---
Overall agreement is increasing to the larger scale pattern with a
weak, ill-formed shortwave across the Lower Ohio Valley driving
the broader large scale trof, especially as the subtropical
wave/low exits the Carolina coast later today.  The 00z UKMET
continues to be a bit too weak and north with the trough as a
whole but as it slides east, the new surface wave along the
frontal zone appears south and weak relative to the remaining
suite.  The 00z ECMWF is similarly weak and generally slow to the
stronger/north 12z GFS and NAM; however, the greater depth through
7H depicts a similar overall evolution to the deeper cyclone to
the GFS/NAM and CMC which are further north.  This makes the QPF
pattern similar to be useful as a slower potential solution, yet
may be less useful in a mass field blend.  So will support a 12z
GFS/NAM and 00z CMC blend with some spot inclusion of the ECMWF. 
Confidence remains slightly below average.

-
...Subtropical TUTT West of California lifting north into the
Pacific Northwest ahead of digging northern stream trough Sun into
Mon...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 12z GFS/ECMWF/CMC blend
Confidence: Slightly above average

19z update: The UKMET is a bit weaker but still has more advanced
moisture from the subtropical stream into the western states
relative to the remaining guidance.  This shift brings it closer
to the initial preference, further increasing confidence toward
this blend.  Still, feel the differences are enough to keep
initial preference rather than increased inclusion of the UKMET at
this time. 

---Prior Discussion---
A strong/compact closed low with origins in the tropics (TUTT
cell) resides off the West Coast of California with a solid
central core and eastern quadrant elongated trof.  The eastern
wave will rotate toward the northern quadrant and help
stretch/elongate the wave toward an approaching deep Gulf of AK
gyre.  As the gyre breaks down and digs with a strong shortwave on
Sunday, it will draw the remaining energy northward toward the
Pacific Northwest late Sunday into early Monday.  Mass fields are
fairly agreeable with some timing/sheared aspects to the wave. 
The UKMET is also drawing higher moisture/wind flow northward
producing broad QPF.  While this system is likely to enhance
thunderstorm (likely dry) environment, the UKMET is likely too
moist and is less preferable.  The 12z NAM shows a bit
stronger/compact solution through the lower depths of the
troposphere, like the UKMET which is a negative tendency toward
the late day 2, early day 3 period...so while it cannot be fully
discounted there are some concerns for inclusion in a blend.  The
ECMWF/CMC are a tad slower than the GFS...but a compromised
location/timing will quite likely verify best given all
considerations available at this time.  As such a 12z GFS and 00z
ECMWF/CMC blend is preferred at slightly 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

This product will terminate August 15, 2020:
www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination.
pdf

Gallina