Spring Valley Lake, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

246
FXUS66 KSGX 200821
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
121 AM PDT Thu Aug 20 2026

.SYNOPSIS...
Monsoonal moisture will increase today and Friday with a slight
chance of afternoon showers and thunderstorms for the mountains
and deserts. There will be some drying of the monsoonal moisture
over the weekend, then maybe a slight increase again for early
next week. High temperatures will remain around 5 degrees above
average for inland areas into next week with low temperatures 5 to
10 degrees above average for inland areas.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

.SHORT TERM (Today through Saturday)...
Monsoonal moisture will increase for today into Friday, then
decrease during the weekend. There is a slight chance of afternoon
showers and thunderstorms for the mountains and deserts for today
and Friday with decreasing chances on Saturday.

High temperatures around 4 to 8 degrees above average for inland
areas today will cool slightly to around 5 degrees above average
for Friday and Saturday. Low temperatures will remain a few
degrees above average near the coast to 5 to 10 degrees above
average for inland areas.

High temperatures will range from the mid 70s to lower 80s near
the coast to the mid 90s to 105 for the Inland Empire with 106 to
112 for the lower deserts. Moderate HeatRisk will continue for the
inland valleys, the Apple and Lucerne Valleys, and the mountains
for elevations below 6000 feet, with moderate to major HeatRisk
for the lower deserts.

&&

.LONG TERM (Sunday through Wednesday)...
There will be some drying of precipitable water for the weekend.
For next Monday and Tuesday for Thermal, ECMWF ensemble output for
precipitable water has about half of the members with values
similar to the higher values for today and Friday with about half
having the same or lower values than the lower values for this
weekend. There will be occasional slight chances for afternoon
showers and thunderstorms for the mountains and deserts depending
on moisture availability.

There will be only slight day to day differences in high
temperatures with high temperatures generally around 5 degrees
above average with high temperatures ranging from the mid 70s to
lower 80s near the coast to the mid 90s to 105 for the Inland
Empire with 108 to 112 for the lower deserts.

&&

.AVIATION...
200500Z....Coast...Patchy low clouds with bases 800-1200 ft MSL are
currently offshore but will slowly spread into coastal areas after
07Z with coverage remaining patchy. Low cloud coverage increases
after 09Z, especially in San Diego County, with areas of clouds
reaching 5-10 miles inland. Local VIS reduced to 3-5 miles on
elevated coastal terrain 10Z-15Z. Expect clearing to the beaches
around 15-16z.

Otherwise...mostly clear through Thursday morning. Slight chance (15-
20%) of SHRA/TSRA over the mtns from 20z Thu - 01z Fri. SCT clouds
based around 10 kft expected regardless of storm development.

&&

.MARINE...
No hazardous marine conditions are expected through Sunday.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT Thursday for San Bernardino and
     Riverside County Valleys-The Inland Empire.

     Extreme Heat Warning until 8 PM PDT Sunday for Coachella Valley-
     San Diego County Deserts-San Gorgonio Pass near Banning.

PZ...None.

&&

$$

PUBLIC...17
AVIATION/MARINE...PG