472
FXUS66 KSTO 182019
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
119 PM PDT Mon Aug 18 2025

.DISCUSSION...

.SYNOPSIS...
A gradual warming trend through the week is expected to peak late
this week, with above normal temperatures accompanied by
widespread Moderate HeatRisk and areas of Major HeatRisk from
Thursday through the weekend. Onshore flow expected to persist,
although generally lighter mid to late week, then becoming
breezier by the weekend. Isolated mountain thunderstorm chances
increase Friday-Sunday along the Sierra from I-80 southward as
well as monsoonal moisture aloft approaches the region.

&&

.KEY MESSAGES...

* Today - Tuesday:
 - Near to below normal temperatures and Minor HeatRisk.
 - Afternoon highs the mid 80s to low 90 for much of the Valley
   and foothills.
 - Periodically breezy onshore flow is forecast at times,
   strongest in the Delta vicinity and over the Sierra Crest with
   good to moderate overnight humidity recovery.

* Wednesday - Weekend:
 - Near normal temperatures Wednesday, trend well above normal
   Thursday into the weekend as high pressure builds back in over
   the Western US.
 - High temperatures in the upper 90s to triple digits expected
   through the Valley/foothills, with limited overnight relief.
 - Probability of Valley/foothills high temperatures > 100F Thu-
   Sat: 60-95%
 - Widespread Moderate HeatRisk and areas of Major HeatRisk
   expected Thursday-Saturday, followed by a gradual cooling trend
   late in the weekend.
 - Dry weather with low daytime humidity in the teens to 20s and
   poor to moderate overnight recovery anticipated mid to late
   week.
 - Monsoonal moisture advection will bring a slight chance of
   afternoon/evening thunderstorms to the Sierra crest south of
   I-80 Friday into the weekend.

.Changes from previous forecast...
 - Temperatures trending slightly upward with widespread Moderate
   HeatRisk and and areas of Major HeatRisk expected through the
   end of the week and into the weekend.
 - Isolated mountain thunderstorm chances potentially linger into
   early next week.

&&

.AVIATION...

VFR conditions next 24 hours across interior NorCal. Sustained
surface winds generally at or below 12 kts, except in the Delta
with west-southwest surface winds 12-15 kts with gusts 20 kts.

&&

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

$$