894
FXUS66 KSTO 211914
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1214 PM PDT Thu May 21 2026



.KEY MESSAGES...

 - Well-above normal temperatures and areas of Moderate HeatRisk
   today-Friday, with low chances for isolated mountain showers
   and thunderstorms.

 - Increased onshore flow this weekend-Monday combined with low
   daytime RHs will lead to elevated fire weather conditions in
   the Valley.

 - Cooler temperatures expected this weekend and into mid next
   week, nearing seasonal normals by Tuesday.

&&

.DISCUSSION...

...Today-Friday...
The warmest high temperatures of the week are expected today as
high pressure riding remains aloft. Highs will be 10 to 20 degrees
above normal resulting in areas of Moderate HeatRisk in the
Valley. Increased onshore flow will aid in keeping temperatures
slightly cooler around the Delta and southern Sacramento Valley.
Temperatures trend slightly cooler tomorrow, but will still remain
above normal.

A weak shortwave develops over Northern California on Friday
which will bring chances (15-20%) for isolated mountain showers
and thunderstorms during the afternoon/evening hours, with
northwesterly flow keeping cells along the crest.


...The Weekend-Wednesday...
Cooler temperatures are on track for this weekend and into early
next week as broad troughing develops over the region,
strengthening onshore flow. High temperatures cool to near-
seasonal for mid to late May by Saturday. West-southwesterly winds
through the Valley will be breezy through the weekend with gusts
15 to 25 mph. Onshore winds peak on Monday as an upper low digs
down from the Pacific Northwest into the vicinity of the Great
Basin. Forecast gusts are between 25 and 40 mph, with the
strongest gusts expected through the Delta, in the northeastern
Sierra foothills, and over the Sierra. Gusty onshore winds
combined with Valley min RHs in the teens will lead to elevated
fire weather conditions Saturday-Monday, despite gradually
improving overnight recoveries.

This gradual cooling trend continues into early-mid next week
when temperatures could fall a few degrees below normal on
Tuesday. A high degree of uncertainty persists on how far
east/west the aforementioned upper low will track and the amount
of moisture associated with it, which could bring chances for
light mountain showers midweek. Forecast confidence will continue
to increase as we approach the weekend, so be sure to check back
for updates.


&&

.AVIATION...
VFR conditions are expected over the next 24 hours. Onshore winds
increase after 20Z Thursday, with some gusts up to 15 kts
possible through 06z Friday in the Valley. Stronger west-southwest
winds 10 to 15 kts with gusts up to 20 kts expected in the Delta
through 18z Friday. Onshore winds will continue to be breezy
tomorrow.


&&

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

$$