Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
153 AM EST Fri Dec 28 2018

Valid Dec 28/0000 UTC thru Dec 31/1200 UTC

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

00Z Model Evaluation...with Final Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 00Z GFS/ECMWF blend
Confidence: Average

The pattern across the lower 48 will feature longwave troughing
over the west-central U.S., bounded by strong subtropical ridging
off of the West Coast and Southeast, with a number of shortwaves
to move through the flow. A closed low forming over the Four
Corners region today is expected to elongate through Saturday with
a portion of the trough pinching off a closed low over
northwestern Mexico while the northern portion shears eastward
toward the northern Mid-Atlantic and Northeast. Meanwhile, a lower
amplitude mid-level wave will reach the Pacific Northwest on
Saturday with two embedded shortwaves with one to progress east
into the northern Plains while the other amplifies into the
Intermountain West.

The closed low over northwestern Mexico Sunday morning is expected
to eject out into the southern Plains with a negative tilt through
Monday morning. The 00Z NAM is significantly faster than the
remaining deterministic and ensemble guidance, the 00Z ECMWF/UKMET
are slower while the 00Z GFS/CMC are in the middle. Given trends
in the ensemble guidance to be toward the slower side since
yesterday and the better support away from the faster 00Z NAM,
will prefer a non-NAM middle ground best weighted between the 00Z
GFS and 00Z ECMWF.

Differences across the Northwest are smaller compared to the
central U.S., but again the 00Z NAM stands out with the downstream
surface low across North Dakota toward the north, with the
remaining models reasonably similar. Regarding the upper trough, a
00Z GFS/ECMWF blend is representative of the non-00Z NAM guidance
and the latest ensemble means, with the 00Z UKMET slower and a bit
more amplified with the upper trough across the West, while the
00Z CMC stands out with a stronger 500 mb trough over the Dakotas
by 12Z/31.

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

Otto