Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
231 AM EDT Wed Oct 03 2018

Valid Oct 03/0000 UTC thru Oct 06/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of 00Z ECMWF and 00Z GFS/00z GEFS Mean
Confidence: Average

06z Update: The timing differences between the ECMWF and GFS with
the developing longwave trough across the western US later this
week and weekend continued with the 00z cycles but perhaps to a
lesser degree. The 00z ECMWF remains a bit slower despite the GFS
also coming in slower compared to its 12z run. The 00z UKMET
continues to be an outlier with the 500 mb heights while the 00z
CMC also is quite different by the end of the period, so the
preference of the 00z ECMWF and the 00z GFS/GEFS mean still looks
appropriate for the mass fields.

---Previous Discussion---
The upper level pattern across the CONUS currently features fast
zonal flow along the northern tier US with one shortwave currently
racing across the Northeast US with another across the Pacific NW.
Offshore the southern CA coast, a closed low was analyzed.
Finally, upstream near the Aleutians, another shortwave trough was
present.

Over the next few days, some phasing of the southern CA low with
the second wave coming into the Pacific NW will lead to large
amplification of the upper level pattern across the US, featuring
longwave troughing for the West with the subtropical ridge over
the southeast US anchoring down. An active storm pattern will
evolve in the middle.

For the initial northern stream energy moving through the Upper
Midwest today and tonight, there is reasonable agreement in the
deterministic and ensemble guidance. The 00z GFS was a bit faster
while the 00z NAM was noted to be stronger with its shortwave.
More spread among the guidance develops by Friday night through
the weekend for the western trough. The 12z UKMET shows a very
different trough structure compared to the rest of the guidance
while again the 00z NAM is more pronounced across the northern US
(and slower/stronger across southwest US) and the 00z GFS faster
compared to the 12z ECMWF, though is trending slower compared to
the 12z/18z runs and lines up fairly well with the 18z GEFS mean.

Across the southern to southeast US, ridging will hold in place
through the weekend, shifting more toward the southeast US and
mid-Atlantic regions by Saturday as the western trough digs.
Fairly tight clustering among all of the guidance, so confidence
here is above average.

Overall, given the fairly tight clustering the first half of the
period followed by timing/strength differences with the western US
trough for the end of Day 3 (00z-12z Sat), a blend of the 12z
ECMWF, 12z EC Ens Mean, and the 00z GFS, 18z GEFS mean seems
reasonable at this time.

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

Taylor