Strong surface high pressure over the Desert Southwest contributed to hot conditions across Southern California for the latter part of July into early August. Many locales broke records along with places in the deserts reaching over 120 degrees at times.
Every event with a place to put it; 7 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS SGX wrote it up.
Strong surface high pressure over the Desert Southwest contributed to hot conditions across Southern California for the latter part of July into early August. Many locales broke records along with places in the deserts reaching over 120 degrees at times. Some areas along the coast also reported dense fog as well.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS San Diego, CA wrote its last area forecast discussion before the first event at Aug 1, 8:37 AM PST, 1 hour 23 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
937 AM PDT Sat Aug 1 2020
.SYNOPSIS...
The heatwave will continue today, except near the coast, where cool
ocean breezes will prevail. Cooling will progress slowly inland
beginning on Sunday as the high aloft weakens and the marine layer
slowly deepens. Westerly winds will increase early next week over
the mountains and deserts as well, becoming quite gusty through and
below passes. Low clouds and some fog will return to coastal areas
as well each night and morning, spreading farther inland next week.
By the middle of next week, seasonally cool weather will prevail once
again.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Two southerly surges are impacting our region this morning, one in
the desert and one along the coast. In the desert, the heat is on
the rise, but lower deserts are running from 9 to 18 degrees off
yesterday's incredible pace at this time of morning. Humidity was
low overnight, allowing for desert areas to cool into the 80s
overnight (unlike early Friday), but a healthier gulf surge has
brought higher dew points and humidity into the lower desert,
explaining the much slower temperature climb this morning. It's
actually quite windy in the Imperial Valley and Yuma. The higher
dew points should mix out some today and allow for a good rise in
temps this afternoon, but may not come very close to the
impressive numbers from Friday, or those in our forecast. A fog
bank developed overnight along the coast in Mexico and the coastal
eddy did not wait for his turn, but cut to the front of the line.
The southerly surge of fog has already shrouded southwest San
Diego County and will be touching most of the county's coast at
times today. Orange County should start getting it late afternoon
and evening. This robust move by the marine layer prompted a
forecast update to accommodate mention of coastal fog during the
day, more coastal clouds overall through evening, and to lower max
temps near the coast. Luckily, this fog is not on the deck, as
visibility at North Island was reported at a non-hazardous 2.5
miles. Patchy dense fog is possible today and tonight, but on the
coastal mesas. That fog bank will have to contend with a very hot
and dry air mass not too far inland. That will make cloud/fog
coverage tricky to forecast tonight into Sunday. Strong high
pressure aloft that has been sponsoring our heat wave has already
begun to relent and will continue to do so as a trough along the
Northwest coast deepens a little over the next few days. This will
feed the coastal eddy, allowing for greater coverage of low
clouds and fog farther inland each night/morning through at least
Wednesday. It will also bring a meaningful cooling trend.
Starting Tuesday we'll begin to see max temps fall below normal.
No real change later next week as the weak West Coast trough keeps
the flow aloft dry from the southwest and temps near to slightly
below normal.
&&
.AVIATION...
011630Z...Coast...Areas of low clouds spreading across the coastal
areas from the south this morning. Bases are 500-700 ft MSL with
tops to 1100 ft MSL, currently impacting KSAN and could impact KCRQ
between 17Z and 18Z. Not likely to impact other TAF sites this
morning. Cigs could scatter out between 18Z and 20Z but low clouds
and fog could linger at the beaches into the afternoon. Elsewhere,
clear through this evening, with areas of smoke near KBUO due to an
ongoing wildfire.
Mountains/Deserts...SCT clouds with bases near 10000 ft MSL over
the mountains after 18Z, dissipating around sunset. Otherwise, clear
with unrestricted vis through this evening.
&&
.MARINE...
No hazardous marine weather is expected through Thursday.
&&
.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 9 PM PDT Sunday for Coachella
Valley-San Diego County Deserts-San Gorgonio Pass Near
Banning.
Heat Advisory until 9 PM PDT this evening for Orange County
Inland Areas-Riverside County Mountains-San Bernardino
County Mountains-San Diego County Mountains-San Diego
County Valleys-Santa Ana Mountains and Foothills.
Excessive Heat Warning until 9 PM PDT this evening for Apple and
Lucerne Valleys-San Bernardino and Riverside County Valleys-
The Inland Empire.
PZ...NONE.
&&
PUBLIC...MM
AVIATION/MARINE...PGThe national radar mosaic for the moment the first event began.
6 excessive heat, 1 dense fog. Local standard time, as filed.
High temperatures of 100 to 110 degrees occurred across the region from July 30th through August 3rd.
Areas of the Coachella Valley heated up to 110 to 120 degrees during this July 30th through August 3rd heat wave, with some areas hitting over 120 degrees on July 30th and 31st. The 122 degree reading on July 31st at the Palm Springs ASOS was one degree shy of the all-time record high temperature at that location.
Areas of the lower deserts of San Diego County reached 110 to 122 degrees during this July 30th through August 3rd heat wave.
Areas of the San Diego County Mountains observed temperatures over 100 degrees during this July 30th through August 3rd heat wave. The COOP observer at Campo reported a high temperature of 105 degrees on both July 30th and 31st.
Parts of the San Diego County valleys reported high temperatures of 95 to 105 degrees on the July 30th through August 3rd heat wave. Hottest days were July 30th and 31st.
Parts of the Inland Empire recorded temperatures from 100 to 110 degrees from the July 30th to August 3rd heat wave.
Carlsbad, San Diego, and North Island ASOS sites reported visibility of 1/4 mile at times throughout the night.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2020Every state in 2020This day in weather historyWarnings in California, August 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 916442, 916444, 916445, 916447, 916449, 916798, 918528.