Harbison Canyon, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

164
FXUS66 KSGX 200415
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
915 PM PDT Wed Aug 19 2026

.SYNOPSIS...
High temperatures for inland areas of around 4 to 8 degrees above
average through Friday will cool slightly to a few to around 5
degrees above average for early next week. Greater monsoonal
moisture on Thursday and Friday and again around Monday of next
week will bring a chance of afternoon showers and thunderstorms
for the mountains and deserts. Night and morning low clouds will
continue for the coastal waters into coastal areas.

&&

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

...UPDATED AVIATION DISCUSSION for 06Z CYCLE...

This afternoon, clear skies are prevailing across the region. The
ridge is at its maximum westward reach today, yielding the
hottest temperatures for the inland valleys this week. Widespread
100F to 105F readings are anticipated across the Inland Empire
with mid to upper 90s in the interior valleys.

Highs Thursday may back off a degree or two, then remain very steady
through early next week, only fluctuating by a degree or two each
day. Today through early next week, highs will hover around 109-113F
in the lower deserts with persistent areas of Major HeatRisk as a
result of overnight lows only falling to the mid/upper 80s, about 5-
8 degrees above average.

The center of the ridge retracts slightly eastward, spinning around
the Four Corners region and opening the door for monsoonal moisture.
Around a 15-25% chance for afternoon isolated showers and a t-storm
Thursday and Friday over the mountains, with lesser chances over the
weekend as the ridge axis moves south and PWAT`s decrease. Chances
for more scattered shower/t-storm activity increase again early next
week as the GFS shows the ridge access rotating and potentially re-
opening the door to more mid-level moisture.

Throughout the forecast period, the marine layer will be fairly
shallow, between 1,000-2000 feet deep, as the influence of the ridge
continues. Low clouds should develop and push up to 20 miles inland
as they typically do in the evening, except for nights with greater
high cloud coverage, which could delay the formation of low clouds.

&&

.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.


&&

.PREV DISCUSSION... /issued 815 PM PDT Fri Aug 1 2025/

SYNOPSIS...
Temperatures near average and marine layer low clouds each night
and morning along the coast and in the western valleys through
Tuesday. High pressure over the Desert Southwest will likely
strengthen by the late next week, bringing a warming trend with
temperatures 5 to 10 degrees above average away from the coast.
There is the potential for monsoon moisture to return late in the
week but precipitation chances remain below 10 percent.

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

This evening, the marine layer is about as deep as it was at this
time yesterday but the low clouds seem slower to increase in
coverage and advance inland. This may be due to a weaker inversion
as a result of some cooling just above the inversion.

From previous discussion...
Our weather continues to be controlled by the dominant upper
ridge currently positioned over southern Arizona and the
low/trough centered over the Gulf of Alaska. As a result, the
marine layer mixed out efficiently today with sunny skies
extending several miles out to sea this afternoon. High
temperatures today coming in right around climatological normals
to 5 degrees below normal - topping out in the 80s to low 90s for
most with 100-110 degrees for the deserts. As we head through the
weekend and into next week, this ridge doesn`t budge much and
stays relatively weak. Still, temperatures increase very gradually
through Tuesday, with high temperatures by Tuesday afternoon only
a couple of degrees warmer than today. The marine layer will
continue to spread inland each night and retreat back to sea each
day with depth varying between 700 and 1400ft.

By the middle part of next week, the center of the ridge slides a
bit closer to New Mexico, but also broadens and strengthens
considerably, bringing more substantial warming for Wednesday and
Thursday. Thursday and Friday will likely be the hottest days of
the next week, with widespread moderate HeatRisk stretching
towards the coasts and high HeatRisk spreading out of the deserts
locally to inland valleys. High temperatures reaching or
exceeding 100 degrees for inland valleys Thurs/Fri with the
deserts likely exceeding 115 degrees (~90% chance). Available
moisture will likely be quite below normal for early August most
of next week, but recover to closer to normal by the end of the
week. Still, chances for any monsoonal thunderstorms by the end of
next week stay low, about 10 percent or less.

AVIATION...
020300Z....Coasts/Western Valleys...Low clouds based 700-1200 feet
MSL are slowly moving inland, reaching its full inland extent by
07Z. VIS reduced 0-5SM over higher coastal terrain and western
valleys. Scatter out Saturday 15-17Z. VFR conditions Saturday
afternoon. Low clouds redevelop at the coast around 04z Sun.

Inland Valleys/Mountains/Deserts...Mostly clear with VFR conditions
through late Saturday.

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

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 Friday for Coachella Valley-
     San Diego County Deserts-San Gorgonio Pass near Banning.

PZ...None.

&&

$$

PUBLIC...Westerink
AVIATION/MARINE...PG