Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
235 PM EDT Sat Oct 06 2018

Valid Oct 06/1200 UTC thru Oct 10/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: Blend of 12Z ECMWF, 12Z UKMET, 00Z EC ENS Mean
Confidence: Slightly below average

---18Z UPDATE---
The 12Z CMC and UKMET did trend toward the ECMWF in the Northwest,
but the GFS remains a flatter scenario with the trough. The CMC
and GFS also continue to be the fastest with the progression of
the potential tropical cyclone. Therefore, the overall preference
remains the same.

---PREVIOUS DISCUSSION---
There are some noteworthy differences between the deterministic
NWP models for the CONUS in the next few days, and ensemble spread
is higher than it has been in recent weeks over much of the West
(associated with the trough) and the Gulf of Mexico (associated
with a potential tropical cyclone). Nevertheless, the large-scale
pattern is fairly predictable and in decent agreement, with a high
amplitude trough in the West and a retreating ridge along the East
Coast. Therefore, forecast confidence is slightly below average
due to important detail differences.

The preference is to lean toward a blend of the ECMWF, UKMET, and
ECMWF Ensemble Mean overall for WPC QPF, even for the potential
tropical cyclone in the Gulf as that will be influenced by the
larger pattern. This is consistent with the medium range forecast,
which also leans more heavily toward the ECMWF.

In the Northwest, the GFS and NAM are much flatter than the other
deterministic models with a digging wave that will arrive on
Tuesday, while the CMC and UKMET develop a closed low. The ECMWF
is a bit of a compromise with greater development of a mid-upper
level cyclone, but not to the degree of the CMC and UKMET. Given
the strength of the associated elongated, sheared mid-upper level
vorticity maximum and accompanying jet streak, we would normally
expect more development of a mid-upper level low than is indicated
by the GFS and NAM. This should have an impact on QPF and thermal
profiles in the Northwest.

Given the flatter upstream wave, the GFS and NAM press the
northern extent of the amplified trough further out into the
Plains, which affects the placement and orientation of the QPF in
that region. The CMC, meanwhile, develops a much stronger southern
stream wave over New Mexico and Texas, which is unsupported by
other models. Because of these detail differences, the preference
is to lean toward the ECMWF, EC ENS Mean and the UKMET which seem
to have a more reasonable forecast of the western trough.

As it relates to the potential tropical cyclone, the CMC maintains
the western extent of the East Coast ridge longer, and this leads
to a more westerly track that generally has less model support.
Additionally, the stronger southern stream trough causes a faster
northward motion and quicker arrival along the Gulf Coast. The GFS
shows faster development of the system, which allows it to
accelerate faster to the north as well. As with the large scale
pattern, the preference is to lean toward the ECMWF here.


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

Lamers