432
FXUS66 KSGX 300400
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
900 PM PDT Sat Jun 29 2024

.SYNOPSIS...
Heat continues to dominate the forecast period with well above
normal temperatures continuing tomorrow in the deserts. A slight
cooldown on Monday will be short-lived before a warming trend sets in
across the region for the rest of the week and into next weekend. A
prolonged period of very hot temperatures will exacerbate any heat
impacts this week. Along the coasts and valleys, the marine layer
will rebuild each evening and linger into the morning hours.

&&

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

Satellite shows the marine layer is already starting to build in
this evening, especially along the San Diego coast. Conditions will
be very similar to Friday night as low clouds and fog creep in and
overspread the coasts and western valleys tonight. The marine layer
should clear out by the late morning and high temperatures will warm
by a few degrees compared to today, around 4-8 degrees above normal.
Rain and thunderstorm chances for the mountains have decreased quite
a bit from the previous forecast, with measurable precipitation
looking unlikely for tomorrow. Otherwise, no significant changes as
extreme heat is still expected to dictate much of the week. If you
have any outdoor plans, make sure to drink plenty of water and limit
your time outside during the hottest parts of day.

From previous discussion issued at 2 PM June 29, 2024....

An interesting synoptic-scale pattern sets up this weekend as
longwave troughing envelopes central California through the
Pacific Northwest and a ridge builds across the Southern Plains,
with increasing heights nudging westward into SoCal. Mid-level
monsoonal moisture could make it into Imperial County and eastern
Riverside County tomorrow, increasing mid-level cloud cover over
the mountains and lower deserts. Some high-resolution guidance
shows small precipitation chances south of the border in the
mountains tomorrow afternoon, so we will continue to monitor
trends to see if cells could pop in our mountains. Further warming
is likely on Sunday across all areas.

The trough axis weakens and moves eastward on Monday ahead of a
strengthening ridge developing off the coast of the Pacific
Northwest. A few degrees of cooling is anticipated on Monday as
onshore flow strengthens.

A weak, but present upper low looks to break off from the mean
flow and settles to our southwest Monday into the middle of next
week while the ridge impinges on the Pacific Northwest. Highs look
to climb a degree or two each day Tuesday through Thursday, and
moderate HeatRisk develops across most inland areas, with high a
HeatRisk in the lower deserts. The presence of that weak low to
the southwest could impact mid-level wind direction and potential
moisture transport around midweek, so trends will continue to be
monitored in regards to monsoonal thunderstorm chances in the
mountains and deserts.

Further warming is possible next weekend as global ensemble
guidance shows the continuation of ridging over much of the
western United States. The degree of warming will depend on the
strength and location of the ridge. Regardless of forecast
uncertainty, we look to be in for a long-duration heat wave
through the first week of July.

&&

.AVIATION... 300300Z...Coast...Low clouds returning to coastal TAF
sites around 05-08Z tonight, with bases of 500-1000 feet MSL and
tops to 1300 feet. Coverage will not extend inland much. Vis 3-5SM
in BR with local vis 1SM on mesas and higher coastal terrain 10-16Z.
Scatter out Sunday 15-17Z. Patchier and less uniform low cloud
coverage Sunday night.

Inland...Westerly winds gusting locally 25-30 knots through Cajon
and San Gorgonio Passes and into adjacent deserts through 07Z.
Mostly clear skies with unrestricted vis will continue through
Sunday, but with SCT cumulus at about 10000 feet mainly over
mountains after 19Z Sunday.

&&

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

&&

.BEACHES...
A long-period SSW swell (from 190-210 degrees) of 2-3 feet at 16-18
seconds will arrive at the SoCal beaches as early as Wednesday
morning. This may lead to elevated surf with breaking wave heights
of 6-7 feet, mainly on south-and-southwest-facing beaches in Orange
County. Rip current risks will accordingly increase as well.
Elevated south swell looks to persist into late next week.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch from Tuesday morning through Friday evening
     for Apple and Lucerne Valleys.

     Excessive Heat Warning from 10 AM Sunday to 8 PM PDT Friday for
     Coachella Valley-San Diego County Deserts-San Gorgonio Pass
     Near Banning.

PZ...None.

&&

$$

PUBLIC...Zuber/EA
AVIATION/MARINE/BEACHES...MM