295
FXUS66 KSGX 270435
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PDT Wed Jun 26 2024

.SYNOPSIS...
Fair weather will prevail through early next week with slight
cooling Thursday through Friday night, especially during the nights,
due to a low pressure trough to the north. Warming will occur again
this weekend as high pressure aloft builds over the East Pacific.
Areas of night and morning low clouds will continue near the coast.

&&

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

Update...

Areas of low clouds were developing along the coast this evening,
with mostly clear skies elsewhere. We still have a lot of moisture
aloft, with 1.73" of total precipitable water in the NKX sounding
from late this afternoon, but the moisture was well distributed
throughout the column and not concentrated in any particular layer,
so impacts of the moisture were rather limited. That moisture will
very gradually decrease through this weekend, mostly Friday and
Saturday as the trough to the north shifts our winds aloft more
westerly. That will be the main impact of the trough as the east-
west oriented high pressure ridge will remain over much of the
southern US and northwestern Mexico. The excessive heat warning will
remain through Thursday in the deserts, even though Friday will have
only slightly lower highs. The heat will build again over the
deserts this weekend, similar to what has occurred or even a bit
warmer than the past few days there.

From previous discussion...

Drying will continue as we get into Thursday and Friday. This ridge
will begin to weaken as a trough across the northern portion of the
West Coast deepens by Thursday into Friday. This will have minimal
impact our weather other than low temperatures slightly cooler than
we have seen over the past few days, with more low cloud coverage
west of the mountains. NBM forecast lows look adequate for the
Friday forecast period, which will have the coolest overnight lows
overall this week. Lows in the low to mid 60s will be prevalent
across areas west of the mountains into the high desert, with lows
in the upper 70s across much of the lower deserts.

High pressure off the West Coast will begin to strengthen into
early next week. NBM probabilities for highs 115 or greater are
around 25-50% across the lower deserts with 60-80% chance of
triple digit heat for the Inland Empire and High Desert by Sunday
and Monday. Low temperatures by early next week will be back in
the 80s across the lower deserts and 65-70 for most areas below
5,000 feet. Global ensembles depict this high possibly
strengthening further into the week, which which would bring well
above average highs away from the immediate coast.

&&

.AVIATION...
270400Z...Coast/Valleys...Satellite shows the marine layer is
beginning to build back in with CIGs around 1400ft MSL at KSAN and
1000ft MSL at KCRQ with tops around 1700ft MSL. Lowering VIS
possible in the valleys beginning around 10z Thursday and continuing
through around 15-16z Thursday, although expect to remain above 4SM.
Similar to last night, the marine layer doesn`t look to make it very
far inland with ample moisture aloft, pushing through coastal Orange
County around 09z and not making it much further than that. Marine
layer scatters out around 17-18z Thursday before CIGs return again
around 02z Friday.

Mountains/Deserts...Gusty north-northwest winds continuing at KPSP
and KTRM through 07z Thursday becoming light and variable through
late Thursday morning. Gusty northwest winds redevelop through the
Coachella Valley as early as 27/22z to as late as 28/02z, with gusts
possibly exceeding 25kts at the terminals and possibly exceeding
40kts through the mountain passes.


&&

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

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning until 8 PM PDT Thursday for Apple and
     Lucerne Valleys-Coachella Valley-San Diego County Deserts-
     San Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...Maxwell (Update)/APR (Previous Discussion)
AVIATION/MARINE...Zuber