Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1246 AM EDT Tue Sep 24 2019

Valid Sep 24/0000 UTC thru Sep 27/1200 UTC

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

00Z Preliminary Model Evaluation with Preferences and Forecast
Confidence
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...CONUS...
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Preference: Non 12Z CMC/18Z GEFS
Confidence: Above average

The guidance is in exceptionally good agreement in the longwave
pattern across the CONUS the next 3 days. A large closed low over
the Hudson Bay, Canada, will shed vorticity impulses across the
northern tier in a fast northern stream through late week. Further
south, a general flat ridge will encompass much of the region from
35N latitude and south, the exception being a slow moving closed
low dropping through the Southwest and into Mexico before
returning to the northeast and slowly becoming absorbed into the
westerlies Friday morning.

For the Southwest closed low, there is little spread whatsoever
until the end of day 3 when the UKMET outpaces the remaining
guidance in its absorption into the fast flow to the north. The
difference in timing and speed is minimal even by day 3, so a
general model blend is sufficient. However, further east, a
shortwave driving a cold front across the middle of the country
and then into the east coast D2-3 begins to feature more
uncertainty as the CMC and GEFS mean slow the progression to
become well west of the mean trough axis by Friday morning. This
seems to be due to a weaker and more strongly kinked 250mb jet
streak in the vicinity of the Great Lakes. While the GEFS and CMC
are actually in pretty good agreement, they are much slower than
the global consensus, and with a fast northern stream anticipate
the faster solutions are more likely.


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

Weiss