Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
209 AM EST Sat Dec 01 2018

Valid Dec 01/0000 UTC thru Dec 04/1200 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: General model blend
Confidence: Slightly above average

---07Z UPDATE---
No change to the preliminary preference. The largest differences
still exist with the ridge developing downstream of the trough
approaching the West Coast early next week. The 00Z UKMET is most
different with the pattern compared to the other deterministic
models and ensemble means, with the ridge axis slightly out of
phase. Therefore, less weight could be placed on the UKMET in the
West.

---PREVIOUS DISCUSSION---
Deterministic model forecasts have converged over the past several
model cycles, and now show a high degree of similarity over the
next few days. This is especially true for most features that are
expected to produce significant precipitation. Therefore, a
general model blend was preferred for WPC QPF in this instance.

The most significant differences existed with the placement of
heavy rainfall in the Southeast, and with the evolving ridge over
the Southwest early next week as a trough approaches the West
Coast.

For the Southeast, the 12Z ECMWF and 00Z NAM tended to place the
heaviest rainfall further northwest. More limited progression of
convective rainfall would be supported by rising mid-upper level
heights and a lack of significant PVA, which should all be
directed further north. However, with the potential for squall
lines, the possibility of faster downstream progression needs to
be considered, and thus a compromise of the timing and placement
is generally preferred.

In the West, the 00Z GFS and 12Z CMC showed more ridging and
warmer temperature profiles early next week. This generally
deviated from model consensus, and the GFS was considerably
further north as compared to the 18Z GEFS Mean. However, the GFS
and CMC were still well within the envelope of ensemble spread,
and we would expect an amplification of a downstream ridge as a
trough approaches the West Coast. Therefore, a general model blend
is still preferred in this region as the GFS and CMC cannot be
discounted.


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

Lamers