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455
FXUS66 KSGX 202112
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
212 PM PDT Thu Jun 20 2024

.SYNOPSIS...
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A warming trend will continue through Saturday with high
temperatures on Saturday as much as 5 to 10 degrees above
average. A shallow intrusion of lower level moisture for the
lower deserts will bring warmer nights with days not quite as hot
for the weekend. There is also a slight chance of showers and
thunderstorms when mid level tropical moisture arrives this
weekend.Then drier and continued hot inland for Monday through
Thursday. Hottest days in the deserts from Monday to Thursday.
The marine layer will continue to keep areas near the coast
cooler but less extensive marine layer coastal clouds especially
during the weekend and slowly returning during the heat wave next
week.
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&&

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

Marine layer clouds mostly gone and boundary layer moisture has
been predicted to thin out along with the shallower marine layer.
This will return tonight but less extensive and less organized.
This weekend it could be completely removed with the mid level
tropical moisture arriving.

The heat wave begins on Friday and peaks on Saturday for coast
and inland valleys as 500 mb heights rise. 500 mb heights rise
to 594 DM this weekend and hold through next week, but the main
difference this weekend is large tropical moisture surge around
the upper ridge. This arrives from the south Saturday and lingers
into Sunday along with low level moisture surge into the lower
deserts. There is sufficient instability and upper level wave so
there is a threat for elevated convection this weekend, then this
becomes more surface based and focused on the mountains and
deserts slopes on Sunday and may linger with isolated cells on
Monday. The threat includes the coastal areas and marine open
waters where precipitable water as high as 2 inches arrives
Saturday night.

The heat advisory remains for the inland valleys and mountains and
the heat watch for more severe heat and major risk remains in
effect for the deserts Monday to Thursday for prolonged heat
wave and highs 110 to 115F and increasing overnight warm lows.
Hottest day is Saturday before mid level moisture arrives. For
late June over 110F becomes critical for lower deserts and this is
along a long duration before the upper ridge weakens temporarily
late next week. Hottest day for deserts looks to be Tuesday and
Wednesday under the 594 DM 500 mb heat dome (upper ridge) across
Socal.
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&&

.AVIATION...
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202025Z...Coast/Valleys...Mostly clear early. after 21/0600Z
areas of low clouds with bases 1300-1500 ft MSL and tops to 2000
ft MSL will spread around 20-25 miles inland with Local VIS 3-5 SM
in BR/FG where clouds near terrain in the valleys, including
VCNTY KRNM. Valleys clearing 14Z-16Z, with coastal areas clearing
16Z-19Z.

Mountains/Deserts...Mostly clear with unrestricted VIS will
continue through Thu evening. West winds with gusts 20-30 kt
through San Gorgonio Pass and on the desert slopes this afternoon
and evening. Most locations will remain dry, and chances for
thunderstorms are currently very low, less than 20 percent. In
fact, there is a good chance that no storms form anywhere across
the region.
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&&

.MARINE...
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A system moving by to the south may bring showers Saturday through
Monday, but current guidance suggests that the thunderstorm risk is
minimal. Otherwise, no hazardous weather is expected through
Wednesday. A Marine Weather Statement has been issued to cover this
hazard.
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&&

.BEACHES...
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Showers and a slight chance of thunderstorm possible Saturday
through Sunday
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&&

.FIRE WEATHER...
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Fuels have dried especially inland were temperatures have been
above normal past 2 months becoming slight below normal levels.
The coast has had little above average marine layer persistence
but is now dropping fuel levels to average but not critical. The
prolonged heat will be a factor in elevated wildfire potential
into next weekend even though some increase in humidity over
weekend.
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&&

.HYDROLOGY...
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Threat for isolated thunderstorms with heavy rain over mountains,
mainly on Sunday but could linger into Monday. Elsewhere there is
a marginal threat for brief showers and isolated thunderstorms
with the arrival of mid level tropical moisture plume this
weekend.
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&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
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CA...Heat Advisory from 10 AM Saturday to 8 PM PDT Sunday for Orange
     County Inland Areas-San Bernardino and Riverside County
     Valleys-The Inland Empire.

     Heat Advisory from 10 AM to 8 PM PDT Saturday for Riverside
     County Mountains-San Bernardino County Mountains-San Diego
     County Mountains-San Diego County Valleys.

     Excessive Heat Watch from Monday morning through Wednesday
     evening for Coachella Valley.

     Excessive Heat Watch from Saturday morning through Thursday
     evening for San Diego County Deserts.

PZ...None.
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&&

$$

PUBLIC/FIRE WEATHER...Tardy
AVIATION/MARINE...Small