FXUS66 KSTO 100937
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
237 AM PDT Thu Oct 10 2024

.Synopsis...
Our cooling trend continues through this week with a weak weather
system bringing light rain late Friday night into Saturday north
of I-80. Below to near normal temperatures are expected to extend
through next week.

.Discussion...
An onshore flow pattern continues today as an upper level trough
approaches from the eastern Pacific. High temperatures will see a
little more cooling today, with relative humidity also gradually
trending higher. This pattern is also spreading high clouds
across the area. Highs this afternoon will be in the mid to upper
80s to low 90s in the Valley and Delta, with 70s to mid 80s
across the lower mountains to the foothills. A shortwave embedded
within the trough along the coast will move closer Friday,
bringing additional cooling. Highs Friday afternoon will drop
another 3 to 4 degrees. By Saturday, highs cool to the upper 70s
to around 80 in the Valley with 60s to 70s over the mountains and
foothills. The NBM projects some warming highs (3-7 degrees)
Sunday as weak eastern Pacific ridging briefly develops ahead of
the next system. HeatRisk levels will remain in the Minor or less
category over the area today through the weekend.

The weak shortwave will bring breezy onshore winds, mainly late
Friday afternoon and evening. It will also bring light precipitation
chances to areas north of I-80. The rain is expected to begin
late Friday night, with best potential early Saturday morning and
then tapering off around mid-day Saturday. Rainfall totals with
this system are forecast around 0.01-0.25", highest along the
far western portions of the Sacramento Valley and the northern
Coastal Range area. Much of the Sacramento Valley is currently
expected to see amounts ranging from sprinkles to a tenth of an
inch, highest over the north end of the Valley.

Some low humidity conditions linger over the mountains and
northern Sacramento Valley today, with afternoon minimums in the
teens to around 20 percent. The onshore flow pattern will bring
increasingly cool temperatures and higher humidity into the
weekend, though, decreasing fire weather concerns further each
day.

&&

.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Weak upper ridging progged over interior NorCal on Monday.
Heights then trend down Tuesday as long wave trough and embedded
short wave in the EPAC approaches. Models differ with progression
of this feature as GFS tracks it through Tuesday night into
Wednesday, while slower EC advertises a Wednesday/Thursday event.
NBM leans towards GFS with timing. EC also showing a wetter wave
with widespread precipitation, while GFS/NBM keep bulk of precip
north of I-80 and mostly over the mountains. GFS then brings
another short wave trough across northern portions of the CWA
Thursday. Areas of gusty wind will accompany passage of short
waves. High temperatures cool through the extended from near
normal Monday to around 3 to 8 degrees below normal midweek.

&&

.AVIATION...
VFR conditions over interior NorCal next 24 hrs. Sfc wind mainly
below 12 kts except vcnty of Delta, SWly wind 15-20 kts til 17z
and after 22z Thu.

&&

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

$$