Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1132 AM EST Thu Dec 06 2018

Valid Dec 06/1200 UTC thru Dec 10/0000 UTC

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

12Z NAM/GFS Model Evaluation...with Initial Preferences and
Confidence
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...Overall Pattern Across the CONUS...
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Preference: General model blend
Confidence: Above average

The primary weather maker through the period is low pressure off
southern California this morning. This low will drift southeast to
northern Mexico as it opens into a neutrally tilted trough through
Friday before reaching the lower MS Valley Saturday and the
southeast coast Sunday. The combination of Pacific and Gulf
moisture allows precipitation to blossom over the southern Plains
and lower MS Valley Friday through Saturday as surface low
pressure develops. Heavy rain threats near the Gulf Coast and
wintry weather threats inland on the north side of the
precipitation shield are expected.

There is relatively good agreement with the upper level open wave
through Saturday as it crosses TX. The trough deepens again
Saturday night over the lower MS Valley with some indication of it
closing again at 500mb; the 00Z ECMWF and 12Z NAM have a brief
close over TX while the 12Z GFS closes over KY/TN. Influence of
the next low descending from the northern Great Plains begins
Sunday. That secondary low is fully in continental air with little
to no associated precipitation. The focus is on the southeastern
CONUS trough that will be a notable winter storm. The 12Z GFS is
still the most progressive model with the surface low off the SC
coast Sunday, though (like yesterday) the 12Z run is less
progressive than the 06Z. The 00Z CMC does start a farther north
surface low track Sunday which is an outlier.

An otherwise equal general model blend will have less CMC included.

The other area of notable precipitation in the CONUS in the 3-day
forecast range is with a trough approaching the coastal Pac NW
Saturday. There is pretty good agreement with the QPF fields
except for the 00Z UKMET which is focused farther north/off the
WA/OR coast. Therefore, a non-UKMET blend is preferred there.

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

Jackson