Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
310 PM EST Wed Nov 28 2018

Valid Nov 28/1200 UTC thru Dec 02/0000 UTC

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

12Z Model Evaluation...with Final Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of 12Z GEFS/00Z ECMWF/ECENS
Confidence: Average

First, the low off New England strengthens in place near
Newfoundland Thursday with little differences in mainly light
precipitation Day 1 among guidance before shifting away from the
CONUS.

A strong shortwave trough approaches the CA coast tonight and is
the main weather maker through the period as it shifts to the
central CONUS. Differences with this low that opens to a wave upon
landfall Thursday begin Thursday night with the 12Z GFS/GEFS mean
reclosing a low at H5 over the Great Basin - a full 24 to 36 hours
(Friday night) before the rest of the 12Z global guidance which
wait until the axis is east of the Rockies to close. Despite the
earlier closing, the 12Z GFS is not as deep with the low on Day 3
which allows a more progressive track and is the main cause of
differences among the guidance. However, the 12Z GFS continues a
trend of less progression with recent GFS runs, so if that trend
continues better agreement can be expected. The 12Z ECMWF is still
the deepest and slowest solution, but is less deep and slow at
12Z. The ensemble means for both systems are similar to the
operational with timing being the main difference. The 12Z UKMET
has much greater amplitude than the flat 00Z and is now in better
alignment with the consensus. However, the preference is still for
a compromised blend of the 12Z GFS leaning toward the 12Z EC
solution is recommended in the model preference.

A second shortwave will reach the Pacific Northwest Friday night
into Saturday. The model differences here are mainly due to the
strength of the east Pacific ridge extending into the Gulf of
Alaska. The 12Z ECMWF is even stronger with this ridge and closes
it into a high quicker (looking ahead into Day 4/5) which will
allow for more shortwave activity into the Pac NW. However, a
general model blend is appropriate through Day 3 given similar
timing and extent of precip across the west.

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

Jackson