000
FXUS66 KSTO 032121
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
121 PM PST Sun Dec 3 2023

.Synopsis...
Shower activity has ended for the area; areas of dense fog likely
in the Valley tomorrow and Tuesday morning, mainly from
Marysville southward. Warm and dry to start the week, then shower
and high elevation snow chances return Wednesday through Friday.
&&

.Discussion...
Latest GOES-18 satellite observations show some breaks in the
clouds for the Valley this afternoon. The trough and associated
moisture that brought showers and high elevation snow showers is
racing off to the east this afternoon. Behind the vacating trough,
an upper level ridge of high pressure is beginning to amplify and
will help usher in warmer temperatures and dry weather for the
beginning of the work week. With our recent rains, light winds,
and limited cloud cover, areas of dense fog are likely to form
Monday and Tuesday morning in the Valley, with the best chances
from Marysville southward. If you encounter fog during the morning
commutes, remember to slow down, never use high beam lights, and
give yourself extra spacing between vehicles. Late Tuesday
evening, there is a chance (10-30%) of precipitation in far
Northwestern Shasta County, as some moisture may race ahead of the
primary system that will bring more widespread precipitation
chances Wednesday.

On Wednesday, a trough from the eastern Pacific will move inland
and bring shower and high elevation snow chances back for the
area. Widespread precipitation will start early Wednesday in the
northwestern counties and spread south and eastward as the day
progresses. Currently, the bulk of the precipitation will likely
be in the Northwestern Counties such as Shasta and Tehama, and for
locations in the Northern Sierra. The National Blend of Models
(NBM) currently has a 60-80% probability of receiving at least one
inch of rain for Redding and areas north and west. For areas
south of Redding, rainfall totals drop to less than 0.50" inches,
with a general 20-60% chance of receiving at least 0.50" inches of
rainfall. Snow levels will be at around 7000-8000 feet at the
onset of precipitation, then lower to around 6000-7000 feet as the
day progresses. Total snowfall accumulations look to be around
1-3 inches for Wednesday, which may make for some slippery
driving conditions and possible chain controls at pass levels.

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...
Thursday will see another shortwave trough move across NorCal in
West-Northwest flow as the parent low moves inland to our north.
Current NBM guidance keeps the bulk of moisture in the far
northwest counties and the Northern Sierra. Friday
afternoon/evening we will start to see some clearing as the trough
moves further to our east and is replaced by upper level ridging
in the eastern Pacific. For Saturday and Sunday, forecast
uncertainty is still high as as models and clusters differ on the
progression rate of the ridge. The NBM has some light rainfall
chances on Saturday evening into Sunday for the mountains and
Northern Sac Valley, but other ensembles such as the GFS and ECMWF
keep the area dry. &&

.AVIATION...


General VFR conditions in the Valley today, with areas of
MVFR/IFR/LIFR in BR/FG from 08Z-19Z Monday (50-80% probability of
1/4 SM visibility, mainly from MYV southward). Local southerly
surface wind gusts of 15 to 20 kts through 00Z Monday, then winds
decrease to below 10 kts. In the foothills/mountains, areas of
MVFR/IFR with lingering showers mainly north of Interstate 80
through 06Z Monday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$