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Model Diagnostics Discussion
(Caution: Version displayed is not the latest version. - Issued 0834Z Aug 15, 2020)
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
434 AM EDT Sat Aug 15 2020

Valid Aug 15/0000 UTC thru Aug 18/1200 UTC

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

00Z Model Evaluation Including Preferences and Forecast Confidence

...Longwave trough expanding across the eastern CONUS into early
next week...
Preference: Non UKMET through 17.12Z
            Non UKMET/GFS D3    
Confidence: Slightly above average

A longwave trough will amplify across much of the eastern CONUS
through the weekend and into early next week.  Through 60 hours,
the mass fields are pretty well aligned with the exception of the
UKMET which features higher heights across the east, with a more
pronounced shortwave ridge into SE Canada D1-D2. A shortwave
trough or even weakly closed mid-level low will develop within the
longwave trough across the OH VLY Sunday morning before ejecting
eastward towards the Mid-Atlantic and offshore by Monday morning.
Again, the spread outside of the UKMET is pretty small with this
feature so a general blend excluding the UKMET is reasonable.

By D3, Monday into Tuesday, the longwave trough axis tries to get
pulled back to the SW and spread increases dramatically. It
appears the evolution of this trough axis will be dependent on
interaction with a shortwave, possibly convectively enhanced /MCS/
rotating atop the ridge to the west and down into the Plains
Monday morning. The GFS appears to be most robust with this
interaction which drives the trough to pull way SW from Sunday,
and becomes out of tolerance with the remaining guidance (again
excluding the UKMET from the blend). While there is little
confidence in timing and evolution of these convectively enhanced
shortwaves at these timescales, outside of the UKMET and GFS the
spread is within the typical D3 tolerance so the remaining models
can be included in the preference.

...Shortwave moving into the Pacific Northwest Sunday night...
Preference: Non UKMET/NAM
Confidence: Average

A potent closed mid-level low off CA Saturday will get pinched
between an expanding ridge over the Southwest and an amplifying
trough digging out of Alaska. This will force the low to open and
shear to the northeast, lifting onshore Washington State Sunday
night into Monday morning. The NAM is quite fast compared to the
remaining guidance with moving this feature to the northeast and
is removed from the blend for its speed. Although the UKMET timing
is well aligned with the consensus, it continues to feature
heights within the ridge that are above the other globals, a bias
it continues, which forces the shortwave to be displaced a bit NW
of the preference.

Model trends at
500 mb forecasts at

This product will terminate August 15, 2020: