An upper level high pressure system over the Desert Southwest led to hot temperatures across Southern California from August 1st through 5th, along with areas of dense fog near the coast on August 1st.
Every event with a place to put it; 14 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.
An upper level high pressure system over the Desert Southwest led to hot temperatures across Southern California from August 1st through 5th, along with areas of dense fog near the coast on August 1st.
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 Jul 31, 7:42 PM PST, 4 hours 18 minutes earlier.
Area Forecast Discussion National Weather Service San Diego CA 842 PM PDT Sat Jul 31 2021 .SYNOPSIS... A trough near the West Coast will guide drier air over Southern California through early next week, effectively ending the thunderstorm threat over the mountains and deserts. High pressure will then slowly rebuild over the Southwest next week, returning hot, dry days inland. It will be warmer along the coast as well, with limited marine clouds and fog. Cooler weather will return by next weekend as the high weakens, a trough redevelops over the West, and the marine layer rebuilds inland. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Thunderstorms have dissipated and left skies mostly clear inland, and only patchy low clouds near the coast. The cores of the heaviest cells were small, so the heaviest rainfall was likely not recorded, but numerous sites measured at least a few hundredths of an inch in the mountains. The greatest report we received was from a site near Big Bear with 0.65 inch. Pine Valley came in second with 0.51 inch. Our 00Z Miramar sounding still had a weak marine inversion based near 1000 FT MSL. The moisture recorded in the entire column had fallen below one inch, signaling, at least a temporary end to our monsoonal activity. No evening forecast updates are planned. From previous discussion... Low clouds will return to coastal areas late tonight, with similar or even slightly lower bases. This may lead to patchy dense fog at low elevations and locally hazardous driving conditions early Sunday morning. Moisture will take a dive Sunday, with PWAT values dropping below 1" for almost all locations, including the lower deserts. This should cut off our chances at additional thunderstorms, although some cumulus may still develop over the mountains. High pressure will then expand westward into the region early in the work week, bringing a notable warmup to inland areas. Temperatures look to peak Tuesday and Wednesday, with highs 113 to 116 F in the lower deserts, and in the low 100's for the Inland Empire and High Desert. Sea Surface Temperatures (SSTs) along the immediate coast of the CA bight are running 1-2C cooler than normal, and this will help moderate temperatures closer to the coast under continued marine layer influence. The rising heights should compress the already shallow marine layer further, keeping most coastal areas free of overnight clouds by Tuesday. With the high pressure center shifting westward, monsoonal activity appears unlikely after today through at least the next week. && .AVIATION... 010300Z...Coast/Valleys...Areas of stratus with bases 400-800 ft MSL will spread back inland after 05Z and up to 10 miles inland by 11Z. Local vis below 1 mile in fog will occur with the possibility of vis less than 1/4 mile on higher coastal terrain and on the coastal mesas overnight, including KCRQ and KMYF. Low confidence in any CIGS in Orange County, and any should be intermittent. Most areas should clear by 17Z. Very patchy stratus possibly developing along the San Diego County coast Sunday night into Monday morning. Mountains/Deserts...Mostly clear with unrestricted vis through Sunday evening. && .MARINE... Patchy dense fog is likely over parts of the inner waters late tonight and early Sunday morning, with visibility less than 1 NM. Wind gusts approaching 20 knots are possible in the outer waters each afternoon through Tuesday. Otherwise, no hazardous marine conditions are expected through Thursday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && PUBLIC DISCUSSION...10/Rodriguez AVIATION/MARINE...SS
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
703 PM PDT SAT JUL 31 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0700 PM DUST STORM BORREGO SPRINGS 33.25N 116.37W
07/30/2021 SAN DIEGO CA PUBLIC
TWITTER REPORT WITH VIDEO OF HEAVY BLOWING
DUST IN BORREGO SPRINGS. CORRESPONDING PEAK
WIND WAS 30 MPH FROM THE SSE AT
APPROXIMATELY 7 PM PDT. MINIMUM VISIBILITY
UNKNOWN. DURATION ESTIMATED.
&&
10The national radar mosaic for the moment the first event began.
10 excessive heat, 4 dense fog. Local standard time, as filed.
Lifeguard dispatch at San Clemente pier reported visibility of zero on the morning of the 1st.
Lifeguard dispatch reports 1/16 mile visibility at Solana Beach. Other federal observations sites reported visibility under 1/4 mile at times.
Multiple reports (not continuous) of visibility of 1/4 mile between 256 am and 656 am at KNRS. Sum of time periods of 1/4 mile visibility was 2 hours 16 minutes.
Lowest visibility less than 1/4 mile at KSDM ASOS. Visibility of 1/4 mile or less occurred continuously from 338 am until 805 am.
Some areas reached near 100 degrees on August 2nd with 90s thereafter.
Hot temperatures occurred where Ontario and Riverside ASOS sites reported 104 degrees on the 2nd and San Jacinto reported 108 degrees on the 4th of the month.
Hot temperatures between 105 and 110 degrees occurred.
Hot temperatures between 105 and 110 degrees occurred.
Hot temperatures between 85 and 95 degrees occurred.
Hot temperatures between 90 and 95 degrees occurred. Idyllwild recorded a high of 93 on the 3rd and 4th of the month.
Very hot temperatures over 115 degrees occurred. Both Palm Springs and Thermal ASOS sites hit 122 degrees on August 4th, making it the hottest August temperature on record for Thermal.
Hot temperatures over 115 degrees occurred. Borrego Springs reached 119 degrees on the 4th of the month.
Hot temperatures between 95 and 105 degrees occurred. Ranchita RAWS hit 105 degrees on the 4th of the month.
Hot temperatures between 95 and 100 degrees occurred. Santee reported a high of 100 degrees on the 2nd of the month.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2021Every state in 2021This day in weather historyWarnings in California, August 2021
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: 979452, 979453, 982237, 982236, 979441, 979442, 979443, 979444, 979445, 979446, 979447, 979448, 979449, 979450.