Perris, California Weather Forecast Discussion

122
FXUS66 KSGX 142025
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
125 PM PDT Sun Sep 14 2025
.SYNOPSIS...
Gradual warming through mid-week, with gradual cooling for the
second half of the week. An influx of tropical moisture will bring
chances of showers and thunderstorms for the middle to end of the
week. Highest chances of showers and thunderstorms will be in the
mountains and deserts, with lesser chances west of the mountains.
The marine layer will become shallower early in the week, with the
potential for minimal or no low cloud coverage for the middle to end
of the week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
At 1 PM, visible satellite was showing low clouds had cleared the
valleys and most coastal locations. Low clouds were lingering along
the immediate coast in southern San Diego County. Weak ridging aloft
early this week will result in a shallower marine layer with low
cloud coverage not reaching much further inland than the western
valleys. For the middle to end of the week, an influx of tropical
moisture from what is now Tropical Storm Mario is expected to move
northward. That influx of moisture will likely disrupt low cloud
and fog formation leaving coverage patchy to nonexistent.
Most valley locations at 1 PM this afternoon were running 3 to 7
degrees warmer than yesterday, with some locations in the mountains
10 to 14 degrees warmer than this time yesterday. The warming trend
will continue for the first half of the week. By Tuesday, the coast
and valleys will be running 5 to 10 degrees above average for this
time of year. The second half of the week is expected to see a
gradual cooling trend. The cooling trend will bring high
temperatures back to below average for most locations by next
Sunday, September 21.
Mid to upper level moisture from Tropical Storm Mario is expected to
become entrained in an upper level area of low pressure off the
coast of Southern California as early as Tuesday. Based on current
guidance, there will be a lack of a strong forcing mechanism on
Tuesday which should result in dry conditions prevailing across the
area although an increase in mid to high clouds can be expected. By
Wednesday, there is expected to be a further increase in moisture
and the environment is expected to become more unstable. Those moist
and unstable conditions are expected to continue into next weekend,
bringing chances for showers and thunderstorms across much of the
area. The highest chances of showers and thunderstorms each day are
in the mountains and deserts (30-60%) but shower/thunderstorms
cannot be ruled out west of the mountains. For areas west of the
mountains guidance is currently showing Thursday and Friday having
the highest chances (20-35%) with lesser chances Wednesday and
Saturday (15-20%). There is still uncertainty surrounding the
details but the majority of ensemble members across model platforms
favor a dry solution for SoCal through Tuesday then a majority favor
a wet solution for Wed through Saturday. Conditions could begin to
dry out next Sunday as we lose access to the moisture from the
south, but for now a chance of showers and thunderstorms remains
in the mountains Sunday afternoon.
&&
.AVIATION...
142000Z...Coast/Valleys...Low clouds have cleared to the coast but
may linger just offshore near KSAN this afternoon. Bases lower
slightly to 1000-1500 ft MSL this evening as clouds move inland
after 02Z Monday. Clouds pushing up to 15 miles inland through 12Z
with a 40% chance of reaching into the western and southern Inland
Empire (including KONT) late. Clouds not expected to be as deep as
this morning. VIS 2-5SM is possible overnight for inland valleys and
for where clouds intersect with terrain. Clearing to the coastline
slightly earlier Monday around 16-18Z.
Mountains/Deserts...Mostly clear and VFR conditions through Monday.
&&
.MARINE...
Tropical moisture will allow for 20-30% chance scattered
thunderstorms over coastal waters Wed-Fri. Any storms that develop
may produce gusty winds and lightning.
&&
.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...CO
AVIATION/MARINE...KW

NWS SGX Office Area Forecast Discussion