669
FXUS66 KSGX 210409
AFDSGX

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

.SYNOPSIS...
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 will be 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.

&&

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

.Evening Update...
Today was the last day with temperatures near to below seasonal
norms for our inland locations who saw temperatures with highs
mostly in the 70s and 80s along and west of the mountains, and
at or below the 110 degree mark across the lower deserts. The
thin marine layer also kept many coastal areas clear making for a
beautiful day near the beaches. Low clouds are slowly beginning to
reform near San Diego this evening. Latest HREF model guidance
hints at most coverage staying near coastal San Diego County, with
less likelihood of any major cloud coverage across Orange County.

The area of high pressure across the Southeast and Southern
Plains of the country will slowly expand westward Friday into the
weekend and warm the area up to above seasonal averages. All eyes
turn toward this weekend as moist southerly flow and instability
make an appearance which has the potential to provide chances for
thunderstorms. Sunday looks to be the peak of the intensity, so
POP forecast from this afternoon is sufficient. This warm air mass
will provide not only warm days but also warm nights. Raised
nighttime temperatures slightly across mountains and high deserts
for Saturday and Sunday nights. Otherwise, minimal changes in the
forecast for this evening.

.Previous Discussion...

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.



&&



&&

.MARINE...
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.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
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.

&&

$$

PUBLIC...APR
AVIATION/MARINE...Maxwell