Lake Arrowhead, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

897
FXUS66 KSGX 040446
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
946 PM PDT Sat May 3 2025

&&

.SYNOPSIS...

A strong area of low pressure will move into the region this
weekend into early next week. This will bring much cooler and
windier weather across inland areas along with increased chances
for precipitation across all of Southern California, where parts
of the deserts may see thunderstorms on Sunday. Rain chances
lower for areas near the coast by Monday with minimal rain chances
by Tuesday across SoCal. A building area of high pressure will
usher in warmer and drier weather by the middle and end of next
week.

&&

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


Evening Update...

The latest models are still showing that the
timing the upper level low to be positioned nearly over Orange
County will be sometime during the early hours tomorrow morning,
which will likely be the best time and highest probability of
light to moderate rain showers along the coastal and inland
locations. The foothills will likely receive the most measurable
precipitation from the morning hours through noon, with some areas
receiving more than a tenth of an inch, or locally closer to a
quarter of an inch for some areas on the western facing slopes in
San Diego County, and more than a quarter of an inch for the
southwestern facing slopes of the San Bernardino Mountains. By
later in the day, this low will begin to transition more eastward
and allow for the instability of the daytime heating and
orographic lifting to provide about a 10 percent chance of
isolated thunderstorms to be possible over the mountains,
especially over the San Bernardino Mountains. This should all
continue to taper off slightly going into the later hours of the
day, although there will be another wave moving though again on
Monday, which will likely provide some additional rainfall of up a
tenth of an inch for the mountains and westward, with lesser
amount tapering off from east to west. The upper level low will
slowly progress eastward and hang around long enough that there
could even be a few lingering showers during the early morning
hours on Tuesday, but then after that the ridge will begin to
build back in with warming and drying conditions by the end of the
week and into next weekend.


From Previous Discussion....

A low pressure system will move into the region through the
weekend bringing late season rain and high elevation snow to the
area. As the low approaches, the marine layer has been slow to mix
out of the area and will likely remain in place over much of the
area through the overnight hours. Drizzle and light rain are
expected overnight at most locations west of the mountains as the
low approaches. Precipitations amounts are generally expected to
be light with a ensemble distributions highlighting the best
chances of 0.10 to 0.15 for most coastal locations and up to 0.25
for the coastal slopes.

Winds will increase through the evening and overnight hours into Sunday
for the mountain and desert passes. A wind advisory has been
issued due to the likelihood of widespread 30 mph gusts, favored
locations like the San Gorgonio will likely see stronger gusts
with the strongest winds possibly approaching high wind warning
values.

Going into Sunday temperatures will remain cool for this time of
the year, with most locations west of the mountains 5 to 10
degrees below normal. Mountains will and the nearby desert will
have an increased chance of an isolated thunderstorm on Sunday,
which could produce an efficient rain event if one forms.
Confidence remains low, about 10% on the potential and location
for any thunderstorm on Sunday, but if one forms it could provide
between half an inch to an inch of rain in under an hour due to
the moist atmospheric profile.

Slight ridging is expected again on Monday between weak systems.
This should allow for a similar marine layer profile, but some
afternoon mixing bringing sunshine into the inland areas in the
afternoon with decreased chances of showers again.

After Monday, a cooler trend sets in as a series of lows move
across the region along with increasing moisture in the lower and
mid levels. For early week, a low off the coast of San Diego will
become an open trough, sweeping across Baja and up through
Southern California, bringing the first chance for some
precipitation early Tuesday morning. At this time, chances remain
low for meaningful precipitation outside of the mountains where
about a 10-20% of some light rain and/or snow showers will be
possible at the highest elevations given snow levels above 8000ft.
Elsewhere, a deepening marine layer may lead to some morning
drizzle, especially for the coastal and valley areas. As the
trough moves up and out on Tuesday the cooler weather arrives,
with highs 5-10 degrees below normal west of the mountains and
slightly above normal for the deserts.

On Wednesday, a low off the coast will begin to push across Central
California, transitioning to a positively tilted trough on
Thursday. This trough will bring significantly cooler
temperatures, 15-20 degrees below normal for some spots, as well
as push some moisture into the area. At the same time, a deep low
pushes down from the north, arriving in southern Nevada by early
Friday morning. Models are in much better agreement today on this
next low, with better agreement on precipitation chances for late
week. Lows both Thursday and Friday in the low to mid 60s along
the coast and in the valleys, 40s and 50s in the mountains, and
60s to low 80s in the deserts. Snow levels will fall to around
6000-6500ft for both days, paving the way for some light snow
accumulations in the mountains. While models are in better
alignment with the upper level pattern for late week, QPF amounts
have generally trended down with the latest model runs, indicating
a higher-confidence in a lower-impact event at this point. Quite
a few things still need to be ironed out with the upcoming system
and how far south it manages to go, but currently the highest
chances (25-35%) for accumulations will be in the mountains. As
the low moves out of the area, a slow warming trend sets in with
weak ridging building and highs look to return to near or slightly
below normal by early next week.

&&

.AVIATION...
040400..Coasts/Valleys/Coastal Slopes...Clouds with varying bases
largely 1500-2500ft MSL are in place across the coastal plain
this evening. Areas of BR/DZ and locally -SHRA are bringing VIS to
2-5 SM with bases below 1000ft MSL. These conditions will likely
persist through the overnight hours and into Sunday morning,
though BR/DZ gives way to more VCSH and bases lifting back to a
more consistent 1500-2500ft.


Desert Mtn Slopes/Deserts...Strong southwest to west winds will
continue through the mountain passes and into the deserts through
the night. Winds peak early Sunday morning with surface gusts 25-35
kt, locally up to 45 kt below the passes. MOD-STG up/downdrafts and
areas of LLWS possible over and east of the desert slopes this
evening and into the early overnight. SCT TSRA will develop over the
deserts and mtns north of San Diego County after 18z Sunday.
Associated up/downdrafts and vis restrictions will be possible with
any storm that develops.

&&

.MARINE...
Gusty west-northwest winds 25-30 kt will continue through the night
over the outer waters with gusts closer to 15-20 kt for the
nearshore waters. In addition to this, combined steep seas of 8-11
feet in the outer coastal waters and 7-9 feet in inner coastal
waters peak Sunday morning and gradually lower Sunday afternoon into
Monday. The Small Craft Advisory remains in effect and contains more
details.

&&

.BEACHES...
West swell of 8-11 feet with a 7-10 second period will generate
elevated surf and a high risk of rip currents starting later today,
bringing hazardous swimming conditions to all beaches. Surf of 5 to
8 feet for San Diego County beaches, with local sets to 9 feet, and
3 to 6 feet for Orange County Beaches is expected. A High Surf
Advisory is in effect from 12z Sunday to 06z Monday. Surf dwindles
down Monday morning in San Diego County, though a building long
period southwest swell may keep surf elevated for both San Diego and
Orange Counties (3-6 feet) through midweek.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory from 5 AM to 11 PM PDT Sunday for San Diego
     County Coastal Areas.

     Wind Advisory until 6 AM PDT Sunday for San Diego County Deserts-
     San Gorgonio Pass near Banning.

PZ...Small Craft Advisory until 11 AM PDT Sunday for Coastal Waters
     from San Mateo Point to the Mexican Border and out to 10 nm.

     Small Craft Advisory until 11 AM PDT Sunday for Waters from San
     Mateo Point to the Mexican Border Extending 10 to 60 nm out
     including San Clemente Island.


&&

$$

PUBLIC...Stewey
AVIATION/MARINE...Munyan