Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1258 PM EDT Sat Aug 24 2019

Valid Aug 24/1200 UTC thru Aug 28/0000 UTC

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

12Z Model Evaluation Including Preferences and Forecast Confidence
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...Overall Pattern Across the CONUS...
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Preference: General model blend
Exception(s): 24/00Z  UKMET/ECMWF blend FL and off Carolinas Days
2/3.
              Non-UKMET across Northern Tier Day 2/3.
Confidence: Slightly above average
            Average for surface low off Carolinas.

NCEP models generally remained strong this forecast period again
providing confidence across much of the CONUS.  There are small
detail differences lingered across the northern tier on Day 3,
with the 24/00Z UKMET a developing/deepening a bit further south,
enough to displace it within the larger guidance suite.  The
24/12Z GFS continued to trend towards a more amplified solution
with the secondary shortwave crossing SW Canada late Monday to
reinforce the broadening closed low into the Red River Valley and
south central Canada by 12z Tuesday.

As the northern stream trof amplifies and digs into the lower
Mississippi River Valley and interacts with the northeastward
shifting tropical wave, the NAM is a bit more separated and
stronger with each feature (typical of bias).  This delays its
eastward progression across the Gulf Coast states relative to the
GFS/ECMWF/CMC.

The 24/12Z GFS continues the short-term trend of a more
eastward/downstream solution with regard to the placement of the
surface wave moving out of FL into the Gulf Stream off the
Carolina coast Sun into Monday.  Like the 24/12Z CMC, the GFS is
weaker than the 24/00Z ECMWF and UKMET.  Still think that the
ECMWF and UKMET were too strong/deep but agree with the previous
shift for a toned-down version of their compromise depth over
other guidance blends.  The 24/12Z NAM is now clearly the slowest
in the envelope of solutions. 

Saw little reason to make changes to the preference with respect
to TS Ivo in the Day 2/3 period.  This is when the surface cyclone
will be weakening/becoming shallow, so steering flow will be
highly determined by remaining convection/depth. Will continue to
favor the 24/12Z GFS solution with respect to moisture transport
into the desert Southwest and given its track record over the last
day or so.

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

Bann