The Weather Prediction Center

Model Diagnostic Discussion

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Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Wed Oct 23 2019

Valid Oct 23/0000 UTC thru Oct 26/1200 UTC

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

00Z Model Evaluation with Preferences and Confidence

Stronger shortwave dropping through Rockies; closing off across
the southern Plains
Preference: 00Z ECMWF, ECENS mean, UKMET blend
Confidence: Below average

07Z update: No big changes noted with the 00Z ECMWF, CMC, and
UKMET now available - all of which still advertise the slower,
closed off solution compared to the NCEP guidance (faster/open)
and in general the forecast confidence did not improve this cycle
and remains below average. From the 12Z to 00Z ECMWF, very little
differences were noted, while the CMC now is solidly the slowest
solution. The ECMWF, its ECENS mean, and UKMET offer the best
continuity and support from the ensembles and a blend of those
solutions would yield a good approach given the trend of the NCEP
guidance toward the non-NCEP models.

---previous discussion---
Shortwave energy currently moving through the central/northern
Rockies will approach the southwest U.S. and southern Plains later
in the week. Model spread and uncertainty remains even at Day 2
and Day 3 with respect how the upper level pattern evolves. There
have been 2 scenarios advertised the last several days, one being
a slower solution with energy pinching off into a closed low over
Texas or a faster/flatter solution with more positive tilted
energy moving into the southeast U.S. and Ohio Valley.

In the last 24 hours, the NCEP guidance (solution 2 above) has
trended toward the non-NCEP guidance (slower/closed low) though
the models still have quite a bit of spread even at Day 2/3. The
00Z GFS still advertises a faster solution, but does close off a
low across the Arklatex region while the NAM closes off over
Oklahoma (compared to the ECMWF/CMC which close off over Texas).
The 12Z UKMET actually lies in between the two sides.

The deterministic ECMWF and CMC may be a bit aggressive and quick
to close off the low and given some of the uncertainty and spread
still, something more along the lines of the ECENS mean could be
useful for a blended approach. This is favored also since there's
been a trend toward the ECMWF like solutions (and not toward the
GFS solutions).

Shortwave troughing across Pacific Northwest Friday-Saturday
Preference: 00Z GFS and 12Z ECMWF blend
Confidence: Slightly above average

The anomalous ridge over the eastern Pacific and western U.S. mid
to late week will be shunted and broken down some as another
strong shortwave trough approaches from the Gulf of Alaska. There
is fairly good agreement in the 500 mb heights as far as timing
and general orientation as the wave reaches the Pacific Northwest.
The 12Z UKMET is noticeably stronger with its energy and digs the
wave a bit further to the south. The 12Z CMC has a similar
solution but not as strong. The GFS/ECMWF/NAM are in fairly good
agreement and within the ensemble spread. At the surface, low
pressure quickly tracks through the Canadian Rockies and most of
the deterministic models have similar strength as it emerges out
in the southern Canadian prairies. The typical biases are seen -
fast GFS, slower ECMWF. As such, the WPC preference is to lean
toward a GFS/ECMWF blend at this point given the relatively good
agreement with just minor spatial details to sort out in time.

Model trends at
500 mb forecasts at


Last Updated: 333 AM EDT Wed Oct 23 2019