The Weather Prediction Center

Model Diagnostic Discussion

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Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
244 AM EDT Sun Oct 21 2018

Valid Oct 21/0000 UTC thru Oct 24/1200 UTC

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

00Z model evaluation...with final preferences and confidence

...Overall Pattern Across the CONUS...
Preference: non 00Z NAM blend
Confidence: Slightly above average

...07Z update...The 00Z ECMWF adjusted faster with the offshore
portion of the cold front approaching the West Coast on Tuesday,
more in line with the remaining model guidance. Elsewhere, the 00Z
UKMET/CMC/ECMWF remained similar or adjusted to the previous
preference leaving only the 00Z NAM as the sole deterministic
model not preferred.

...previous discussion follows...
The synoptic pattern across the CONUS through Wednesday morning
will feature mean mid-upper level troughing over the northeastern
quadrant of the U.S. with the breaking down of a rex block along
the West Coast as an upper trough axis swings across on Tuesday.
The departure of a sharp upper trough along the East Coast this
morning will be replaced with a broader trough across the Great
Lakes/Northeast Tuesday evening. Out West, a slow moving upper
trough/closed low will translate eastward from California today
toward the Four Corners region Tuesday night.

Across the Northeast, there is generally good agreement with the
mid to lower levels but the 00Z NAM, 00Z GFS and 12Z ECMWF match
closest to the latest ensemble means.

Across the Southwest into Texas, trends have shown convergence
with the timing of a trough axis slowly moving east, but the 00Z
NAM is significantly faster with Tropical Storm Willa and
associated moisture (see below section) which may have impacts on
rainfall across portions of New Mexico.

Out West, there is good agreement throughout except for the 12z
ECMWF which is a bit slower with a cold front nearing the West
Coast on Tuesday, mainly west of northern California. However, the
differences over land are small enough that the ECMWF can be
included as part of a general blend.

A 00Z GFS/12Z ECMWF blend can be used from the West Coast to the
East Coast through Wednesday morning.

...Tropical Storm Willa...
Preference: 00Z GFS/00Z ECMWF blend closest to 03Z NHC advisory
Confidence: See NHC products

...07Z update...Despite having trended quicker and east from their
12Z cycles, the 00Z UKMET/CMC remain significantly slower than the
03Z NHC advisory for Willa. The 00Z ECMWF adjusted a bit faster
but remains slow compared to the NHC advisory. A ECMWF/GFS blend
still appears best for Willa given their blended position matches
closest to the NHC track.

...previous discussion follows...
The 00Z NAM is considerably faster with Willa and its remnants as
the system makes landfall in western Mexico. Meanwhile, the 12Z
UKMET/CMC are much slower and west than NHC. A blend of the 00Z
GFS and 12Z ECMWF appears closest to the latest (03Z) NHC advisory
for Willa but the GFS is a bit faster and the ECMWF a bit slower.
For the latest information on Tropical Storm Willa, see the
official NHC advisory.

Model trends at
500 mb forecasts at


Last Updated: 244 AM EDT Sun Oct 21 2018