O'Brien, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

962
FXUS66 KSTO 060834
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
134 AM PDT Sun Oct 6 2024

.Synopsis...
Well above normal temperatures continue into early this week,
with widespread Moderate to Major HeatRisk in the Valley, Delta,
and Foothills. Slight (5-15%) chance of high elevation mountain
showers Sunday and Monday afternoon along the Sierra Crest;
gradual cool down begins Tuesday with possible shower chances
north of I-80 and higher elevations late this week.

.Discussion...
Another unseasonably hot October day is in store for interior
NorCal with widespread Moderate to Major HeatRisk to accompany
triple digit afternoon highs. Upper level ridging located in the
Four Corners Region continues to dominate the synoptic pattern,
which is also weakening the cooling impacts of the Delta Breeze,
leading to warm overnight lows in the mid to upper 60s and low
70s. The Heat Advisory will continue until 11 PM tonight, with
some considerations of possibly extending the Advisory until
Monday, as temperatures have trended up from previous forecast
model runs.

As mentioned above, temperatures are forecast to remain in the
upper 90s to around 102 on Monday, with the hottest temperatures
once again in the Delta, southern Sacramento and Northern San
Joaquin Valleys, and the Foothill thermal belts. A weak embedded
trough riding along the ridge will introduce slight shower chances
(5-15%) along the Sierra Crest Sunday evening and Monday evening,
but no significant precipitation or thunderstorms are anticipated
at this time. We will finally start to see some relief from the
oppressive heat that has made early Fall feel more like Summer, as
the ridge will begin to breakdown and PacNW troughing will begin
to influence our synoptic pattern. With troughing returning, we
will see high temperatures slowly start to fall, although they
will still be warmer than what is climatologically normal for this
time of year by 5-12 degrees. Overnight lows will also see a
return to the mid 50s to low 60s Tuesday.

Wednesday, troughing will continue to remain in the PacNW, and
heights over NorCal will somewhat flatten, which will induce
westerly flow and more cooling across the area. High temperatures
will be in the upper 80s to low 90s, with the 90s forecast in the
northern Sacramento Valley. Attendant HeatRisk will be Minor
across the region, finally breaking the stretch of Moderate to
Major HeatRisk.

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...

Cooling trend Thursday into Friday as heights/thicknesses trend
down in response to short wave trough in the EPAC approaching the
West Coast. Models continue to handle this wave differently with
GFS showing a more dynamic system but keeps the track farther
north into the PacNW than EC. At this time it appears some light
precip possible over Shasta county Friday into early Saturday.
Main impact looks to be additional cooling Friday with increased
onshore flow. Below normal high temperatures expected Friday.
Upstream upper ridging then modeled to build into NorCal over the
weekend resulting in warming temperatures with highs near to
slightly above normal.

&&

.AVIATION...

VFR conditions over interior NorCal next 24 hrs with sfc wind
generally below 12 kts except lcl NW-NE sfc wind to 15 kts with
gusts to 20 kts in the foothills/mtns til 18z Sun.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 11 PM PDT this evening for Carquinez Strait
and Delta-Motherlode-Northern San Joaquin Valley-Southern
Sacramento Valley.

&&

$$