042
FXUS66 KSTO 220916
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
216 AM PDT Tue Oct 22 2024

.SYNOPSIS...
Seasonable temperatures and generally dry weather are expected to
persist this week, with unsettled weather returning over the
weekend into early next week.

.DISCUSSION...
A quiet pattern is expected today with light onshore flow, dry
weather and slightly cooler high temperatures than Monday. These
highs are about normal for this time of year, in the 70s to
near 80 in the Valley and lower foothills, and in the 50s to 70s
in the upper foothills and lower mountains. Little change is
expected through Friday.

A shortwave trough brushes by to the north over southern Oregon
and far Northern California, with weak eastern Pacific ridging
building in behind it starting Wednesday afternoon. The day will
start out cool, with Valley and Delta lows in the mid to upper
40, but afternoon temperatures will trend a few degrees warmer
than today. Precipitation is expected to remain mainly north of
the area, though completely can`t rule out some isolated light
mountain shower chances over far northeastern Shasta County. Much
of interior Northern California will be mostly clear. Behind this
trough, some increased northerly flow is expected Wednesday night
into Thursday, along with a warming and drying trend as the
eastern Pacific ridging builds back into the area through the
rest of the week. Forecast highs are in the upper 70s to low 80s.
Daytime relative humidity around 15-30%, lowest on Thursday on the
west side of the Valley, where some northerly winds gusting to
20-25 mph are possible. The flow pattern shifts to more onshore
Friday afternoon as a Pacific trough approaches and the ridge axis
shifts eastward, with increasing humidity levels and cloud cover
over the area.

&&

.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)...
Ensemble guidance and cluster analysis has an upper level trough
off the coast by early Saturday. The trough is then projected to
move onshore sometime later in the weekend into early next week
bringing an unsettled weather pattern back to interior northern
California. The NBM currently shows the potential for light
precipitation beginning over the northern Coastal Range Saturday
afternoon/evening, with chances becoming widespread north of
Interstate 80 on Sunday. The National Blend of Models (NBM)
continues to show a 40-80% probability of a tenth of an inch or
more of precipitation over 48 hours through Monday night, with the
best chances over higher terrain and north of Interstate 80.
There is a 25-65% probability of a quarter of an inch or more.
Cooling temperatures and increased onshore flow are also
anticipated with the troughing over this period. Some clusters are
also suggesting the trough digging southward over the Great Basin
for the middle of next week with ridging building in over the
eastern Pacific, leading to the potential for some increased
northerly flow developing behind the trough. Significant
uncertainty remains, though, so we will be closely monitoring the
situation.

&&

.AVIATION...
VFR conditions over interior NorCal next 24 hrs except isold MVFR
possible in HZ/FU vcnty of Shoe Fire in Shasta Co. Sfc wind
mainly below 12 kts.

&&

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

$$