995
FXUS66 KSGX 291604
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
904 AM PDT Sat Jun 29 2024

.SYNOPSIS...
Gradual warming through this weekend followed by minor cooling on
Monday. A prolonged heat wave is expected for inland areas Tuesday
into at least next weekend, including for the Fourth of July
holiday. Night and morning low clouds and fog will continue along
the coast and far western valleys through much of next week.

&&

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

Update...
The 12z Miramar sounding showed a 9C degree inversion based near
1500 feet and a saturated profile as low as 1060 feet. Low clouds
extended through the coast and western valleys but are quickly
eroding as of 9 AM, with most areas expected to clear by late
morning. Some patches of low clouds could persist at the coast due
to the strength of the inversion, but most areas should be mostly
sunny today. Today will be warmer than on Friday, with highs
generally topping out 2-5 degrees above normal.

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.

Previous Discussion (Issued 250 AM PDT Sat Jun 29 2024)...
A warming trend will take place this weekend as an upper level
high centered over TX expands westward towards So Cal. By Sunday
high temperatures will be around 5 to 8, locally up to 10, degrees
above normal. Highs in the lower deserts will be as much as 114
degrees, with highs in the low 100s across much of the Inland
Empire. The persistent marine layer will keep the coastal areas
and to a lesser extent the inland valleys somewhat moderated, with
highs in the 70s near the coast and mid 80s to low 90s for inland
Orange County and much of the San Diego County Valleys. An
Excessive Heat Watch remains in place for the lower deserts
beginning on Sunday morning.

Brief cooling occurs on Monday as a weak upper level trough moves
inland across the West Coast and causes the upper ridge to retreat
eastward. Most areas will see highs around 2 to 5 degrees lower
than Sunday.

An upper level high over the East Pac slowly shifts east over CA
and eventually into the Great Basin as it strengthens through the
week. However, there are still a lot of spread amongst the global
ensembles regarding the placement and strength of the upper level
high, especially beyond Wednesday. For the Fourth of July, The
warmest solutions which accounts for 20 percent of the ensemble
space has the high centered over CA and NV, while 69 percent of
the ensemble members have the high still centered off the
coast/not as hot in So Cal. By next weekend it is more decidedly
warmer with about 80 percent of the ensembles placing the high
somewhere across the southwest or Great Basin. The GFS remains the
most aggressive with the strength of the high, peaking at 600 dm
next weekend, though only 10-20 percent of the GEFS members show
heights of 600 dm or more. Meanwhile, no EPS members show heights
that high. Needless to say, there is still a bit of uncertainty
with regards to the exact high forecast temperatures - add in
potential monsoon moisture in the lower deserts and the
uncertainty increases even more. Given the position and strength
of the high, thunderstorm probabilities are fairly low - generally
10 percent or less.

Regardless of the forecast uncertainties, we are in for a long
duration heat wave whether temperatures end up falling in the low
end or high end of the current forecast range, especially in the
deserts. The Excessive Heat Watch for the lower deserts currently
extends into Friday, while the timing for the high deserts has
been adjusted to start on Tuesday and lasting into Friday. Heat
Advisories will likely be needed for additional areas as the
event draws closer.

&&

.AVIATION...
291550Z...Coast/Valleys...Low clouds currently extend about 15 miles
inland by with local VIS 2-4 miles on higher coastal terrain, bases
600-1500 FT MSL and tops to 2000 FT MSL. Expect clearing to the
coast 16Z-18Z but patches of low clouds could persist at the beaches
through this afternoon. Low clouds returning to coastal TAF sites
around 05-08Z Sunday, bases at or slightly below 1000 FT MSL
expected.

Mountains/Deserts...Mostly clear skies with unrestricted VIS will
continue through this evening. Westerly winds gusting locally 25-35
kt will return to the desert slopes and adjacent deserts and through
San Gorgonio Pass this afternoon/evening.

&&

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

&&

.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 Watch from Sunday morning through Friday evening
     for Coachella Valley-San Diego County Deserts-San Gorgonio
     Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...EA
AVIATION/MARINE...Adams