Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
338 PM EDT Sat Aug 31 2019

Valid Aug 31/1200 UTC thru Sep 04/0000 UTC

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

12Z Model Evaluation, Confidence, and Preferences
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...Overall Pattern Across the CONUS...
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Preference: Non-NAM blend
Confidence: Above average

19Z Update: With the rest of the 12Z guidance available, it
appears that the 12Z CMC trended more toward the rest of the model
solutions with the northern U.S. shortwave on Day 3. As a result,
its solution can be incorporated with the model preference blend.
No other significant differences were noted across the remainder
of the CONUS through 84 hours. 

---previous discussion---
The general synoptic pattern across the CONUS is expected to
feature troughing over the Great Lakes and eastern U.S. with
building ridging over the southwest U.S. through the next 84
hours. A stronger shortwave trough will swing through the northern
Rockies into the northern Plains by early next week. In the large
scale sense, most of the latest operational and deterministic
guidance is in good agreement. The 00Z CMC digs the northern tier
shortwave too much beyond 48 hours while the 12Z NAM is a bit too
amplified as well. The earlier bias seen in the GFS being too fast
seems to have resolved itself this cycle such that it can be
incorporated more.

Overall, a non-NAM, non-CMC blend would suffice for the mass
fields across the rest of the CONUS. For the latest model
preference and track proxy for Dorian, see below.


...Hurricane Dorian...
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Please refer to the official National Hurricane Center forecast
track

Initially, the guidance that aligns with the latest official NHC
forecast track is a consensus/blend of the 06Z GEFS, 12Z NAM, and
12Z GFS (through 60 hours). Beyond that time frame, the forecast
track lies near the middle of the deterministic and operational
consensus. The CMC is much faster compared to the rest of the
guidance and the UKMET is slower and to the southwest. Past 60
hours, the GFS/NAM are on the eastern fringe of the model spread
while the ECMWF, while slower, is a decent proxy as well.

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

Taylor