Guasti, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

386
FXUS66 KSGX 222141
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
141 PM PST Mon Dec 22 2025

.SYNOPSIS...
An Atmospheric River will bring widespread heavy rain and mountain
snow above 8000 ft late Tuesday into Wednesday, with more scattered
showers continuing into Thursday (Christmas Day). Gusty southerly
winds can be expected across much of the area, including near the
coast and over the coastal waters on Wednesday. There are additional
chances for widespread rain, mountain snow, and elevated winds in
the mountains and deserts Friday through Sunday with decreasing
chances into Sunday.

&&

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

Key Points:

* Widespread moderate to heavy rainfall Christmas Eve with the
  potential for roadway flooding and localized flash flooding from
  the coast to deserts. Rapid rises in small streams and increased
  flow in main stem rivers expected.

* Snow levels are forecast to remain above 8000 ft into Christmas
  morning, increasing potential for rock and mudslides along
  mountain highways, and debris flows in and below burn scars,
  especially in the San Bernardino County mountains.

* Gusty southerly winds are expected across the area with wind gusts
  30 to 45 mph on Wednesday for the coast and valleys and Tuesday
  afternoon through Thursday evening for the San Bernardino
  mountains and High Desert. Make sure to secure outdoor furniture.
  Tree damage is possible.

* Additional chances of rain, wind, and mountain snow Thursday night
  through Sunday. Snow levels are expected to lower to 6500-7000 ft
  by Friday morning and 5000-5500 ft by the weekend creating slick
  conditions on mountain highways.

An Atmospheric River is still on track to impact Southern California
on Wednesday. Periods of light to locally moderate rain may begin as
early as mid-day Tuesday with increasing chances of precipitation
into the overnight hours. Overnight Tuesday locally heavy rain may
develop, most likely on the coastal slopes of the San Bernardino
County mountains. The heaviest and most widespread rain is expected
through the day Wednesday, with the heavy rain moving northwest to
southeast from Orange County to San Diego County deserts. After the
rain band passes, scattered showers are expected to continue with
locally heavy rain into Thursday morning (Christmas Day). Latest
guidance shows a significant decrease in IVT (atmospheric moisture)
during the day Thursday, bringing the potential for periods no
precipitation. Snow levels are expected to remain quite high through
the duration of the heaviest precipitation, but are expected to
lower later in the week. Please see the Hydrology section below for
more information on expected rainfall rates, totals, and snow level
information. In addition to periods of heavy rain, gusty south winds
are expected. South winds are expected to increase on Tuesday
afternoon, with the strongest winds expected during the day
Wednesday. Peak wind gusts of 60-70 mph, locally up to 80 mph
possible on the coastal slopes of the San Bernardino County
mountains with gusts 45-65 mph into the High Desert. Winds will stay
elevated in San Bernardino county mountains and High Desert into
Thursday. For the coasts and valleys gust of 30-45 mph are expected,
with the strongest winds expected with the main band of rain.

There still remains some uncertainty in the upper level pattern for
late Thursday through Sunday. Global models continue to struggle
with the progression of the low pressure system that develops near
the Gulf of Alaska. The solutions with more ECMWF ensemble members
show a faster eastward movement of the low which would bring
additional chances of more widespread precipitation to the area as
early as late Thursday continuing into Friday, with scattered light
showers or dry conditions by the weekend. Solutions with more input
from GEFS members show a slower eastward progression of the low
which would continue our precipitation chances into at least Sunday.
In addition to rain and mountain snow chances winds are expected to
increase over the mountains and into the deserts, with timing of the
strongest winds dependent on timing and position of the incoming
trough. We will have to see how this evolves over the next few days,
but overall the rain for late into the week into the weekend looks
far less impactful, though snow could make travel difficult in the
mountains should the snow level lower enough.

&&

.AVIATION...
222100Z....Coast/Valleys...Fog has cleared the southern portions of
the San Diego coast with the Orange County coast clearing after 20Z.
Low clouds will linger along the immediate coast in areas through
the afternoon, before moving back onshore after 23/00Z. Bases
initially 700-900 ft MSL will steadily rise overnight, likely to
above 1500 ft MSL by 12Z Tuesday, and clouds will spread to cover
the coastal basin. Areas of DZ early Tues morning will locally lower
cigs/vis through the end of the TAF period.

Otherwise...SCT-BKN high clouds with unrestricted VIS continues
through Tuesday morning.

&&

.MARINE...

No hazardous marine conditions expected through Tuesday morning. An
approaching storm system will lead to strengthening winds and
building seas beginning Tuesday afternoon. Winds initially around 15-
20 kts gusting to 25 kts Tuesday afternoon will increase late
Tuesday night, potentially to gale force with wind gusts upwards of
30-35 kts. This will bring steep seas of 7-10 feet. Additionally,
periods of moderate to heavy rain Wednesday will lead to areas of
poor visibility. Strong winds and steep seas are expected to
continue through early Thursday morning. Winds will weaken slightly
by Thursday morning, but likely remain hazardous to small craft
through most of the day. Winds weaken and turn northwesterly
Friday.

&&

.BEACHES...
Frontal winds begin to make their way into the area Tuesday night
into the early morning hours wednesday creating gusty winds and
elevated surf heights of 6 to 8 ft. This will create hazardous
swimming conditions at area beaches through Saturday morning.

&&

.HYDROLOGY...
While moderate to locally heavy rain may begin Tuesday evening
(especially for the mountains)guidance is coming into better
alignment that the heaviest and most widespread rainfall is expected
through the day Wednesday. Rain will move from northwest to
southeast through the day Wednesday, with scattered showers
lingering into the overnight hours and Christmas morning. Those
scattered showers may be locally heavy. Additionally there is a
slight chance of thunderstorms for Wednesday evening into early
Thursday morning and heavy rain is expected where thunderstorms
develop. Peak rainfall rates are expected to range from 0.5-1 inch
per hour, with the potential to be locally higher where embedded
convective showers or thunderstorms develop. The coastal slopes of
the San Bernardino mountains are expected to receive a significant
amount of rainfall due to strong southerly flow aloft (30-50 kt)
allowing for orographic enhancement of rainfall and the warm airmass
preventing snow formation below 8000 ft during the heaviest
precipitation.

For the San Bernardino/San Gabriel Mountains Tuesday afternoon
through early Thursday the current deterministic forecast is:
- Cajon Pass westward: 7-10", locally higher
- East of Cajon Pass: 5-8"

For remaining areas current deterministic forecast for Tuesday
afternoon through early Thursday is:
- Orange County: 3-4", highest north
- Inland Empire: 2.5-4", highest northwest
- San Diego County Coasts/Valleys: 2-3.5", highest north
- Santa Ana Mountains: 3-5"
- Riverside/San Diego County Mountains: 3-5"
- High Desert: 1.5-3", highest west
- Low Deserts: 0.75-1.5", locally 2.5" near the San Gorgonio Pass

The higher rainfall amounts in the deterministic ranges above will
likely be more localized to where heavier, more convective bands of
rainfall develop.

Most of the precipitation across southwestern California through
Christmas morning is expected to fall as rain with snow levels
remaining above 7500-8000 feet. Snow levels could drop to 6500-7000
ft by Friday morning, potentially down to 5000-5500 ft by the
weekend.

The San Diego River at Fashion Valley and the Santa Margarita River
at Ysidora are currently expected to reach Action/Monitor stage.
Based on current forecast, the San Diego river is expected to peak
at 8.9 ft early Thursday morning with the Santa Margarita expected
to peak at 11.5 ft late Wednesday night. Interested parties should
continue to monitor the river forecast as the forecasted peak and
timing are highly dependent on the timing of the heaviest rainfall.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory from 11 PM Tuesday to 11 AM PST Saturday for
     Orange County Coastal Areas-San Diego County Coastal Areas.

     Wind Advisory from 3 AM to 10 PM PST Wednesday for Orange County
     Coastal Areas-Orange County Inland Areas-San Bernardino and
     Riverside County Valleys-The Inland Empire-San Diego County
     Coastal Areas-San Diego County Valleys-Santa Ana Mountains
     and Foothills.

     Flood Watch from late Tuesday night through late Wednesday night
     for San Diego County Coastal Areas-San Diego County Deserts-
     San Diego County Mountains-San Diego County Valleys.

     Flood Watch from Tuesday afternoon through Wednesday evening for
     Apple and Lucerne Valleys-Coachella Valley-Orange County
     Coastal Areas-Orange County Inland Areas-Riverside County
     Mountains-San Bernardino County Mountains-San Bernardino
     and Riverside County Valleys-The Inland Empire-San Gorgonio
     Pass near Banning-Santa Ana Mountains and Foothills.

     High Wind Watch from Tuesday afternoon through Thursday
     afternoon for Apple and Lucerne Valleys-San Bernardino
     County Mountains.

PZ...Gale Watch from Tuesday afternoon through Wednesday afternoon
     for Coastal Waters from San Mateo Point to the Mexican
     Border and out to 10 nm-Waters from San Mateo Point to the
     Mexican Border Extending 10 to 60 nm out including San
     Clemente Island.


&&

$$

PUBLIC...CO
AVIATION/MARINE/BEACHES...Villafane