Granite Hills, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

399
FXUS66 KSGX 100420
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
920 PM PDT Fri May 9 2025

.SYNOPSIS...
The marine layer low clouds and fog spread inland as early as
Monday but low clouds will be limited to the beaches this weekend.
Saturday will likely be the hottest day of the year so far, with
high temperatures as much as 20 to 25 degrees above normal for the
inland valleys. A cooling trend begins on Sunday as a low pressure
system approaches, with much cooler conditions by Monday, and
Tuesday looks like the coolest day next week. Gusty winds will
accompany the low pressure system for Monday and Tuesday with the
strongest gusts found in the mountains and deserts. Gradual
warming back to near normal for late next week.

&&

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

This evening...The marine layer is very shallow, with low clouds
and fog currently restricted to within a couple of miles of the
beaches. High-resolution models indicate a weak, short-lived eddy
tonight and there is some evidence that it is developing. This
could allow the marine layer to deepen a little and spread low
clouds and fog a little farther inland tonight than previously
anticipated.

From previous discussion...
The ridge of high pressure aloft peaks in intensity tonight into
Saturday, setting the stage for the hottest day of the year so
far. Ensemble mean guidance is supporting high temperatures in the
Inland Empire reaching 101-103, locally near 105 with highs near
97 across the San Diego County inland areas, locally 99-101 in
valleys. With this, the Heat Advisory has been expanded to include
the San Diego County inland valleys for Saturday afternoon. These
temperatures will be about 20-25 degrees above normal for mid
May, a stark difference from what was seen earlier this week when
the marine layer was keeping highs in the upper 60s to low 70s for
many. The ridge axis begins to shift eastward into Sunday in
response to a low pressure system moving in from the northwest.
This will initiate the beginning of a cooldown, with highs 5 to
10 degrees cooler than Saturday.

With the persistent subsidence from the upper level ridge, the marine
layer will likely be even lower than this morning/afternoon, but
will likely be a bit more patchy in coverage. For land areas, the
greatest coverage of low clouds for Saturday morning is expected
in San Diego County from the coast inland to around the mesas
with the fog locally dense near the mesas and other higher coastal
terrain. Less certain is how much deepening and inland spread of
the coastal low clouds will occur for Saturday night into Sunday
morning. The most likely scenario is for the low clouds to return
into portions of the western valleys by Sunday morning ahead of
the next low pressure system.

A large low pressure system off the Pacific Northwest coast
Sunday morning moves ashore and deepens southward through
California Monday into Tuesday. While this system will likely not
feature much in the way of precipitation, it will bring a
pronounced drop in temperatures, a much deeper marine layer, and
gusty winds for the mountains and deserts. As quickly as the
temperatures rose late this week, they will cool just as quickly
with the incoming trough, as high temperatures will fall to as
much as 15 to 20 degrees below average in the mountains as
early as Tuesday. High temperatures on Tuesday will range from
the lower to mid 60s near the coast to the 60s for the valleys
with the lower deserts in the mid 70s to lower 80s. Night and
morning low clouds are expected to return to portions of the
inland valleys by Monday morning, then onto the coastal slopes of
the mountains for Monday night and Tuesday. There will be stronger
onshore flow for Monday and Tuesday with stronger and gusty
southwest to west winds in the mountains and deserts. The
stronger gusts, 45 to 55 mph, are expected in the northern
Coachella Valley below the San Gorgonio Pass with isolated gusts
of 60 to 70 mph.

The main axis of the upper trough passes by Wednesday morning, and
while weak troughing lingers into late week, Wednesday into
Thursday will be less cool than Thursday, inching closer to near
normal by Friday. For Wednesday and Thursday, the marine layer
won`t be quite as deep, but coastal low clouds will spread into
portions of the inland valleys for Wednesday night into Thursday
morning.

&&

.AVIATION...
100330Z..Coasts/Valleys...Satellite shows low clouds have started to
push inland across parts of San Diego County with bases ranging from
200ft MSL closer to Imperial Beach up to 600ft MSL near Camp
Pendleton. Clouds will continue to slowly push inland overnight,
remaining patchy, unlikely to make it more than 5-10 miles inland,
with these bases prevailing through Saturday morning. FG and BR with
VIS down to 1-5SM likely across most coastal areas and western
valleys, with localized areas of VIS down to 1/2SM or even 1/4SM,
especially for the coastal mesas. Highest confidence for one hour of
more of a CIG at KSAN (35-50%) and KCRQ (30-40%), while KSNA is
around a 30% chance. The worst conditions will be generally between
08z-14z, with conditions quickly improving after 14z as clouds clear
out. Full clearing to the beaches should occur by 16z-17z where the
clouds may linger into the afternoon. Less confidence in low
clouds/FG for Saturday night into Sunday morning, with around a 10%
chance of impacts at KSAN.

Mountains/Deserts...Mostly clear with VFR conditions through
tomorrow. Some gustier winds Saturday morning through the early
afternoon possible in the Coachella Valley where BLDU may briefly
reduce VIS.

&&

.MARINE...
Low clouds and patchy fog will  bring visibilities to 1-3SM over the
waters tonight through tomorrow afternoon, locally under 1SM. Please
see the Marine Weather Statement (MWSSGX) for more details. West
winds will strengthen by Monday and Tuesday leading to increased
confidence on wind gusts reaching small craft strength across the
outer waters.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT Saturday for San Bernardino and
     Riverside County Valleys-The Inland Empire.

     Heat Advisory from 10 AM to 9 PM PDT Saturday for San Diego
     County Valleys.

PZ...None.

&&

$$

PUBLIC...PG
AVIATION/MARINE...Zuber