Alpine, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

221
FXUS66 KSGX 191549
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
849 AM PDT Sat Jul 19 2025

.SYNOPSIS...
Slight chances for showers and thunderstorms in the mountains
this afternoon. Dry conditions will return for Sunday through
next week. Temperatures will remain mostly below seasonal averages
even for inland areas. Marine layer low clouds and fog will reach
into portions of the valleys each night and morning.

&&

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

.Morning Update...

A deeper marine layer is present this morning via satellite
imagery. Clouds pushed all the way into southern parts of the
Inland Empire with a stratocane visible off the coast of Orange
County making for a fun satellite picture this morning. Clearing
to the coast is expected over the next few hours. This morning`s
sounding yielded a decrease in precipitable water values, near
1.25 inches. The drying atmosphere will make storms harder to form
today. Hi-res models do not show a lot of storm activity in the
mountains today, but cumulus clouds may be able to produce a
couple of weak storms by the afternoon. The atmosphere dries out a
bit further by Sunday, but will continue to watch for minimal
chance of weak thundershowers on that day as well. Otherwise, next
week is looking quiet with the forecast remaining on track.

.Previous Discussion (225 AM Saturday)...

After the tstm activity from yesterday afternoon, conditions have
begun to dry out as the upper low moved north and is now roughly
centered over San Diego County. However, sufficient monsoonal
moisture remains for there to be about a 20 percent chance of
showers/tstms over the mtns this afternoon as daytime heating
becomes a factor. Showers/tstms will likely be fewer and weaker
than yesterday afternoon. Hourly rainfall rates are unlikely to
exceed 0.25 inches per hour. High-resolution ensembles indicate
about a 10 percent chance of exceeding 0.20 inch per hour. By
Sunday, conditions have become dry and stable enough that the
chances for afternoon showers/tstms are negligible, although some
cumulus clouds could form over the mtns. The marine layer has
begun to assert itself this morning as the upper low moves almost
directly over San Diego County and the sub-tropical high has
shifted eastward over TX. Low clouds currently extend inland to
the foothills in San Diego County and into the southern portions
of the IE. Northeast flow aloft over San Bernardino, Riverside and
Orange Counties is likely preventing the marine layer low clouds
from spreading into the northern portions of the IE.

For Monday through the end of next week...the pattern will be
dominated by low pressure troughing over the west coast, with the
sub-tropical high centered over the gulf states. This will keep
the monsoonal moisture out of SoCal and allow for a robust marine
layer presence, with low clouds and fog spreading into the inland
valleys each night and morning. It will also keep temperatures
near or a little below seasonal averages for most of the region
including the lower deserts. Model solutions are in fairly good
agreement through the coming week with respect to the overall
pattern, however there is still some spread among the solutions
with respect to the details of the forecast.

&&

.AVIATION...
191530Z....Coast/Valleys...Low clouds based 1400-1700 feet MSL
will eventually scatter out to the coast by 18-20Z. But only
partial or intermittent clearing is expected at the immediate
coast. Low clouds with similar bases will move back inland after
20/01Z, moving farther into inland valleys tonight, with a 40%
chance for cigs at KONT after 20/09Z. Scatter out Sunday will be
similarly late, around 18-20Z.

Mountains/Deserts...ISO TSRA (15-20% probability) 20-00Z over
mountains, with CU/CB bases 8000-10000 feet MSL, tops to 35000 feet.
Erratic wind gusts, strong up/downdrafts, and VIS restrictions
possible with any TSRA. Skies clearing after 00Z.

&&

.MARINE...
No hazardous marine weather expected through Wednesday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC...APR/PG
AVIATION/MARINE...MM