Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
304 AM EDT Sat Oct 27 2018

Valid Oct 27/0000 UTC thru Oct 30/1200 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 NAM and GFS, and 12Z UKMET
Confidence: Slightly above average

---07Z UPDATE---
The 00Z UKMET trended closer to the ECMWF with a slower
progression of the wave in the northern stream while the 00Z CMC
trended faster (closer to the GFS and NAM). The preference was to
remain with the preliminary assessment for the final WPC QPF.

---PREVIOUS DISCUSSION---
Deterministic NWP models are in good agreement with their mass
fields and QPF through 29/00Z (Sunday evening), at which point
some differences begin to emerge. These differences are most
notable from the Northern Rockies into the Northern Plains where a
progressive and lower-amplitude wave will begin to erode a
downstream ridge and produce a more zonal flow pattern overall.
The 12Z ECMWF and 12Z CMC show a stronger ridge, with higher
heights over the Northern Plains, and a slower eastward
progression of the wave. A slow bias is not uncommon in the ECMWF,
and thus the preference was weighted more toward the excellent
agreement between the 00Z NAM and GFS, and 12Z UKMET. Given the
evolution to a more zonal flow pattern, and the eroding trough in
the Northeast, there doesn't appear to be much downstream of the
wave to slow its approach.

The stronger ridge and slower wave progression on the ECMWF did
appear to affect its QPF, with lighter amounts in the Northern
Rockies and different placement in the Northern Plains. Otherwise,
a general model blend will probably suffice outside of these areas
as model agreement is fairly good overall. Most of the
deterministic model height fields are contained well within the
ensemble spread.


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

Lamers