Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
342 AM EDT Tue Oct 01 2019

Valid Oct 01/0000 UTC thru Oct 04/1200 UTC

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

00Z Final Model Evaluation with Preferences and Forecast Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: ECENS/ECMWF/UKMET/GEFS through day 2, ECENS/GEFS day 3
Confidence: Slightly below average

07Z Update:
Spread by day 3 is considerable, and has increased with the 00Z
Non-NCEP suite. The UKMET sped up a bit with its trough in the
west, while also amplifying the shortwave ridge across the Plains.
A more amplified pattern suggests a slower progression of the
trough, so the 00Z UKMET seems to be trending in the wrong
direction. The CMC sped up the western trough while also
de-amplifying the middle ridge, which is logical, and is now more
in line with the remaining guidance. The ECMWF slowed and
amplified, which also makes sense but is against the general trend
of a faster solution. Appears the best course of action by day 3
is to stick close to the GEFS/ECENS mean which show some amplitude
differences but reduce the overall spread.

Previous Discussion:
Two areas of concern through the forecast period as an anomalous
western trough/eastern ridge begins to break down.

The first is the evolution of that western trough as it fills and
lifts northeast through the Great Lakes on D2 and into New England
on D3. Although this feature is likely to weaken and move quickly
in the pinched flow, the GFS is likely much too fast and outpaces
all the available guidance as well as its own ensemble mean. The
CMC takes up the other end of the spectrum, falling well behind
the consensus mean. This leaves the UKMET/ECMWF/NAM, and while the
NAM looks reasonable aloft, its surface evolution of a backdoor
cold front towards the Mid-Atlantic is likely too strong, so the
ECMWF/UKMET as well as the ECENS/GEFS are preferred in the east.

The other feature is a renewed longwave trough digging into the
west coast on D3 from the Gulf of Alaska. Once again, the GFS is
much too fast, and in this case it is clearly due to a more zonal
Pacific Jet streak showing much less equator-ward mass transfer
than the remaining guidance. This keeps the trough flatter and
faster through the west. Although there is considerable
latitudinal and longitudinal spread, the UKMET/ECMWF/GEFS/ECENS
are in pretty close agreement and show better run-to-run
consistency than the remaining models. For this reason, and since
that is the preference for the east as well, believe this blend is
sufficient for the entire CONUS.

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

Weiss