Valley Of Enchantment, California Weather Forecast Discussion

901
FXUS66 KSGX 181615
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
915 AM PDT Thu Sep 18 2025
.SYNOPSIS...
Moisture from the remnants of Tropical Storm Mario will peak
today, then decrease into the weekend. Showers and scattered
thunderstorms will move northward across the area today with the
mountains and deserts the most likely locations for heavier
rainfall with the most likely time for the heavier rainfall from
late morning through early evening. There will be gradual drying
and warming for Friday and Saturday. For early next week, there is
greater uncertainty with the placement of low pressure to the
northwest and high pressure to the southeast and the resulting
temperatures and the potential for tropical moisture from the
southwest to move into the area.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.Morning Update...
Partial clearing is seen on satellite this morning for areas west
of the mountains. Hi-res models continue to show minimal
additional precipitation for this reason throughout the day, but
chances remain as the environmental conditions may support more
shower development. The forecast remains on track to see heavier
shower and thunderstorms cells to begin to form over the mountains
and deserts by the middle of this afternoon through the evening
hours. HREF model 90th percentile values show hourly rain rates
over 0.75" across portions of the San Diego/Riverside Co
mountains. Any of these storms may produce heavy rainfall and
lightning, which may lead to localized flooding. Minimal chances
for precipitation are expected for the weekend into next week as
an area of low pressure moves closer to the coast, which may help
funnel in weaker tropical moisture.
.Previous Discussion...(257 AM PDT Thursday)...
.SHORT TERM (Today through Saturday)...
Moisture from the remnants of Tropical Storm Mario will peak
today, then decrease into the weekend. Showers and scattered
thunderstorms will move northward across the area today with the
mountains and deserts the most likely locations for heavier
rainfall with the most likely time for the heavier rainfall from
late morning through early evening.
A Flood Watch continues for the mountains and deserts from 5 AM
PDT today to 2 AM PDT Friday. Bands of thunderstorms tracking
across the same area would be the most likely scenario for
producing heavier rainfall totals. The most likely peak hourly
rainfall is one-half to one inch with isolated maximum hourly
rainfall to 2 inches. There will be decreasing chances for
showers and thunderstorms for late tonight through Friday, limited
mostly to the mountains and deserts for Friday afternoon.
High temperatures for today will range from the mid 70s to around
80 near the coast to the 80s for the Inland Empire with the lower
to mid 90s for the lower deserts. That is as much as 10 to 15
degrees below average for the higher mountains in San Bernardino
and Riverside Counties. The coast and valleys will cool on Friday
with slight warming for the mountains and deserts.
There will be warming of a few degrees for inland areas on
Saturday. Saturday high temperatures will range from the mid to
upper 70s near the coast to the mid 80s to lower 90s for the
Inland Empire with the mid 90s to around 100 for the lower
deserts. That is generally a few degrees below average to around
5 degrees below average for the higher mountains.
&&
.LONG TERM (Sunday through Wednesday)...
There are differences in the placement of low pressure to the
northwest and high pressure to the southeast with greater spread
in the resulting high temperatures and in the potential for
tropical moisture from the southwest to move into the area.
There is a greater number of ensemble members of the GFS for the
warmer and drier solutions and a greater number of ensemble
members of the Canadian model for the cooler and wetter solutions
with about an equal weighting of ECMWF ensemble members for either
of those scenarios. The calibrated NBM has chances for showers at
around 20 percent for Sunday through Tuesday, but with low
confidence in the details.
&&
.AVIATION...
181600Z....Coast/Valleys...-SHRA with isolated TSRA will continue to
be possible through this evening, although chances are lower than
this morning. Main cloud bases will remain between 8000-10000ft MSL.
Satellite shows a swath of low clouds with bases around 700-800ft
MSL have developed along the coast, currently impacting KSAN and
KCRQ. Low clouds are expected to clear out over the next few hours,
but SCT-BKN clouds closer to that 10000ft MSL deck will likely
prevail for much of the day. Any precipitation should come to an end
by 06z Friday. Patchy lower clouds around 900-1500ft MSL possible
late tonight into Friday morning generally after 10z.
.Mountains/Deserts...Higher terrain intermittently obscured. After
19Z, SHRA/TSRA chances shift to the mountains and deserts. Bases
generally above 10000ft MSL but in areas of heavier RA, bases could
briefly lower to around 3000ft MSL with vis 1-5SM. Some TSRA could
produce strong up/downdrafts, frequent lightning, and CB tops to 35
kft. The widespread precip moves out to the north tonight into
Friday, with additional SHRA/TSRA chances for Friday afternoon.
&&
.MARINE...There is a slight chance of thunderstorms through early
Friday morning, with the greatest chance being this afternoon. Any
storm could briefly produce lightning, gusty erratic winds, and
choppy seas. Otherwise, no additional hazardous marine conditions
are expected through Monday.
&&
.BEACHES...There is a low chance of lightning (5-10%) through early
Friday morning, with the greatest chance being this afternoon.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch through late tonight for Apple and Lucerne Valleys-
     Coachella Valley-Riverside County Mountains-San Bernardino
     County Mountains-San Diego County Deserts-San Diego County
     Mountains-San Gorgonio Pass near Banning.
PZ...None.
&&
$$
UPDATE...APR
PUBLIC...17
AVIATION/MARINE...Zuber

NWS SGX Office Area Forecast Discussion