000
FXUS66 KSTO 191130
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
330 AM PST Sun Jan 19 2020

.SYNOPSIS...
Some fog possible in portions of the Central Valley and mountain
valleys this morning. Mostly dry and mild today with precipitation
returning late Monday into Wednesday.

&&

.DISCUSSION...
Upper ridging near 120W this morning with considerable amounts of
baroclinic cirrus feeding into it from approaching mid latitude
wave. Despite higher clouds, some fog has developed overnight in
portions of the Northern San Joaquin Valley. Potential for patchy
fog to further develop north into the Southern Sac Valley and
Delta overnight. Fog lifted into stratus deck yesterday in the
Northern San Joaquin Valley. This likely to occur again today and
will be slow to dissipate, if at all, under abundant higher cloud
cover. Rising 1000-500mb thicknesses will lead to slightly warmer
temperatures today for most areas in the CWA with highs near to
slightly above normal.

Second mid-latitude wave approaches Monday but weakens and gets
drawn into progressing long wave. Associated baroclinic zone
weakens as it approaches the coast. A stronger Pacific frontal
system follows quickly behind it and begins to spread associated
precip into the Coastal range and northern portions of the CWA
Monday night. Surface winds increase Monday night as front draws
closer. Widespread precip then spreads over interior NorCal
Tuesday morning as frontal system moves inland. Snow begins in the
mountains of Western Plumas and Northern Sierra Nevada Tuesday
morning. Bulk of associated precip moves through during the day
Tuesday. Post-frontal showers Tuesday night into Wednesday can be
expected, especially over our eastern mountains. Snow levels
start out around 4000 to 5500 Monday night, lowering to 3500 to
4500 feet by Wednesday morning. Model QPF has decreased some from
previous runs and suggests snowfall amounts of 4-12 inches
generally AOA 5000 feet with locally higher amounts over Lassen
Peak. Rainfall amounts in the Central Valley range from under a
tenth in the Northern San Joaquin Valley to above half an inch in
the Northern Sacrament Valley. Around an inch of rain is expected
in the wetter foothills locations. Breezy Tuesday as the front
moves through with locally windy conditions over higher terrain.

Precip turns showery Tuesday afternoon into evening with fropa.
Lingering showers possible overnight into Wednesday morning,
mainly over the mountains. Drier weather expected midweek with
warming temperatures as upper ridging returns. Weak waves moving
through the ridge will keep a slight chance of light showers over
the Coastal and Shasta mountain Wed/Thu, otherwise dry with some
night/morning valley fog likely.

PCH

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...
The beginning of the forecast period will start out dry, under
upper level ridging. The exception will be some light showers,
mainly over the northern mountains. Forecast highs in the Valley
will be in the upper 50s to low 60s, with mountain locations in
the mid 30s to low 50s. Uncertainty arises late in the period as
model guidance suggests the potential for widespread precipitation
next weekend, but confidence is low given model disagreement.
Specific details will likely change so stay tuned.

&&

.AVIATION...
VFR conditions next 24 hours, except for periods of MVFR
conditions, locally IFR/LIFR, mainly south of KMYV through 18z-20z
today due to BR/FG.

&&

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

$$