Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1151 PM EST Sat Jan 12 2019

Valid Jan 13/0000 UTC thru Jan 16/1200 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: Non-CMC blend, with a strong lean toward
            12Z EC ENS and 00Z GEFS Means on West Coast
Confidence: Above average; except below average in West

The model diagnostics and preference can basically be divided into
the areas east and west of the Continental Divide. For areas to
the east, model agreement is quite good and once the coastal low
begins peeling away 24 hours from now, expected precipitation is
very limited. The pattern will be dominated by broad surface high
pressure and weaker, more zonal flow aloft. A surface low will
push through southern Canada, but associated precip should just
graze the far northern portions of the Great Lakes. The main
difference here is that the 12Z CMC is notably less amplified with
the departing trough relative to all other deterministic models,
and therefore the CMC is excluded from the preference. Otherwise,
a general model blend is preferred.

Meanwhile, to the west of the Continental Divide, there is far
greater model disagreement particularly after Monday afternoon
(15.00Z). These differences emerge as the rex block over the
interior West begins to break down. Some models (00Z GFS, NAM; 12Z
UKMET) take the closed low off the California coast, open it into
a trough, and kick it onshore, while other models (12Z ECMWF, CMC)
just concentrate the closed low and associated vorticity maxima
further north off the N CA coast. There are not strong and clear
trends, and the differences between the models lead to very
different QPF. The mass field preference here is to lean toward a
blend of the ECMWF and GEFS ensemble means, given the lack of
agreement. However, it wouldn't be too surprising to see an
eventual trend toward a weaker wave breaking off and kicking into
southern California on Monday Night, with the trough/low reloading
further north by Tuesday off the Northern California coast. This
would mean a stronger wave into southern California than the
ECMWF/CMC currently indicate, as well as more focused
precipitation into C/N California by late Tuesday.


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

Lamers