Twin Peaks, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

304
FXUS66 KSGX 202105
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
205 PM PDT Fri Sep 20 2024

.SYNOPSIS...
A low pressure system moving across southern California will
continue to bring scattered thunderstorms for this afternoon and
early evening in southwestern San Bernardino and western
Riverside Counties, with the greatest potential for heavier
rainfall in the San Bernardino Mountains and the Mojave desert.
For Saturday through Monday, dry with a warming trend with high
temperatures warming to around 5 degrees above average for inland
areas on Monday. Generally fair weather with seasonal temperatures
will continue for Tuesday through Thursday, but with greater
spread in the temperature guidance for the coast and valleys.

&&

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

This afternoon...The low pressure system over SoCal is moving
quickly eastward and should be over the lower Colorado River
valley by late this evening. It`s producing scattered showers and
tstms over much of the region. Tstms cover much of southwestern
San Bernardino County and western Riverside County. Currently,
there are no storms in Orange or San Diego Counties but the storm
cells are moving to the southwest in the flow around the upper low
and could reach those counties later this afternoon and evening.
At least for a relatively brief period before the low and
associated dynamics moves too far to the east.

From previous forecast...
Temperatures today will remain well-below seasonal averages, as much
as 15 to 20 degrees below average for the mountains and inland valleys,
with high temperatures for the Inland Empire mostly in the 70s.

Dry and warmer conditions are expected this weekend. On Saturday,
greater warming is expected for the mountains and deserts with
slower warming for the coast and valleys. Warming will continue on
Sunday with the greater warming for the coast and valleys. High
temperatures on Sunday will return to around seasonal averages,
with high temperatures in the mid 80s to mid 90s for the Inland
Empire and around 100 for the lower deserts.

The warming is expected to continue into Monday, with high
temperatures for inland areas around 5 degrees above average,
mostly in the 90s for the Inland Empire and around 105 for the
lower deserts.

The marine layer will persist and low clouds will cover much of
the area west of the mtns tonight. each night and morning.

Generally fair weather with seasonal temperatures will continue
for Tuesday through Thursday, but with greater spread in the
temperature guidance for the coast and valleys.

&&

.AVIATION...
202030Z...SCT to locally BKN low clouds based at 2500-3500 ft MSL
present along the coast into inland San Diego County.

Meanwhile, BKN cumulus/CB and thunderstorms based at 7-10k ft MSL
extend from the San Bernardino and Riverside mtns into the northern
Coachella Valley and the Inland Empire. These are moving CCW around
a low pressure system, which is currently over northern SD/south-
central Riverside counties but moving east rapidly. Thunderstorm
chances continue for the aforementioned areas as well as the eastern
Santa Ana mtns, most likely through 00Z this evening as the low
pressure moves off to the east but isolated storms could continue
through 02Z. Lightning, erratic and gusty winds, local moderate
up/downdrafts, and reduced vis in locally heavy rain expected near
thunderstorms.

Mid-level clouds will clear late this evening into the overnight
inland, but low stratus clouds rebuild again along the coast between
03-06z this evening, with bases around 2000-2500 ft MSL lowering to
around 1500-2200 ft MSL early Sat AM. These will move inland to
cover the entire coastal basin overnight. Clouds clearing to the
coast 17-19Z Sat, with otherwise clear skies Sat.

&&

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

&&

.HYDROLOGY...
A low pressure system moving across southern California will
continue to bring scattered, mostly light showers and thunderstorms
for this afternoon and early evening. The low will move
southeastward across southwestern San Bernardino and western
Riverside Counties this evening. The greatest potential for any
heavier rainfall is in the San Bernardino and Riverside County
Mountains. Hourly rainfall rates of up to four-tenths of an inch
will be possible, with totals of up to one-half in the San
Bernardino Mountains by about 8 pm.

The most likely location for any mud and debris flows from recent
fires would be with the Line Fire in San Bernardino County. While
much of the higher resolution guidance shows peak hourly rainfall
rates to around four-tenths inch, there is greater uncertainty in
the timing of any heavier rainfall during the afternoon. Some of
the guidance has the peak earlier in the afternoon while some of
the more recent HRRR model guidance is later in the afternoon,
between about 4 and 7 pm.

The current local NAM-bounded WRF model solution is showing an
overall slight slowing of this low pressure system. Indications
are now for showers/tstms persisting in extreme southwestern San
Bernardino County and western Riverside County until 7-8 pm today.

&&

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

&&

$$

PUBLIC...PG
AVIATION/MARINE...CSP