A persistent ridge across the Desert Southwest allowed for enhanced monsoonal moisture across Southern California from July 17-19. A Flash Flood Watch was issued for the Riverside County Mountains and the San Diego County Mountains for July 18.
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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.
A persistent ridge across the Desert Southwest allowed for enhanced monsoonal moisture across Southern California from July 17-19. A Flash Flood Watch was issued for the Riverside County Mountains and the San Diego County Mountains for July 18. Thunderstorms produced heavy rainfall in the mountains, where several flood advisories were issued on July 17 and July 18. A cluster of elevated thunderstorms formed across northern San Diego County and progressed westward to the coast early on the morning of July 18.
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 16, 8:13 PM PST, 3 hours 47 minutes earlier.
Area Forecast Discussion National Weather Service San Diego CA 913 PM PDT Fri Jul 16 2021 .SYNOPSIS... High pressure over the Intermountain West will strengthen and bring increasing monsoonal moisture to Southern California this weekend. Thunderstorms are possible, mainly in the mountains and deserts each afternoon and early evening next week. A wave of moisture and instability will bring clouds and sprinkles or very light showers to the entire region late Saturday through Sunday morning. Marine layer clouds in the coastal areas will continue rather patchy each night and morning. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Update: Dry weather prevailed across Southern California today. Highs across our service area ranged from 72 degrees at Oceanside Harbor to 114 at Ocotillo Wells. Dry weather is expected to continue through Saturday morning. Thunderstorms over western Arizona are producing westward moving outflows. However, this is still a ways from the CA border and hi-res models keep any impacts well east of our area tonight. So a quiet night is expected. This will change things by Saturday afternoon though, at which time isolated thunderstorms will be possible over the mountains as enough mid/high level moisture may move in by then to allow a few cells to develop. Sunday afternoon looks more active with a further increase in moisture, so thunderstorms will be more likely then over the mountains and parts of the deserts. Previous Discussion (Issued at 122 PM PDT Fri Jul 16 2021): Skies were mostly sunny this afternoon with some cumulus over the mountains. Fair and seasonal weather and temperatures will continue this coming week, with a few interesting features. High pressure aloft will build over the four corners area this weekend, then migrate to the central Rockies next week. This will put SoCal in the favorable southeast flow for monsoon moisture to arrive in our region. There is a slight chance of showers and thunderstorms in mainly our mountains Saturday afternoon. Things get more interesting after that as an easterly wave or inverted trough in that southeast flow moves across SoCal. This presents our biggest forecast puzzle to solve. There is a range of possibilities for weather Saturday evening through Sunday morning, from widespread showers and isolated thunderstorms anywhere, to simply pretty clouds overhead and only isolated showers in the mountains. We know; that's a big range of possibilities. The most likely scenario has been put in our forecast: sprinkles or really light isolated showers anywhere across the entire region Saturday evening through Sunday morning. The more confident pattern will take over Sunday afternoon with chances of thunderstorms in the mountains and deserts, particularly the high desert. The more predictable, diurnal nature of showers and thunderstorms will continue for much of the week, a small chance of thunderstorms each afternoon in the mountains and locally in the deserts. On Monday and Tuesday the monsoon valve turns down the moisture volume, so any thunderstorms are less likely and more isolated and confined to mountains. The ridge axis puts SoCal in more moist easterly flow once again Wednesday and Thursday to increase our chances of thunderstorms across a wider area of the SoCal interior. Friday is a wild card with equal parts of guidance showing a decrease in moisture as a West Coast trough develops (turning the upper flow from the drier southwest) but other guidance showing a continuance of Thursday's moisture. For now we're carrying another afternoon chance of tstorms for the mountains. The following weekend does seem to lean toward a drier solution with that trough taking greater control. Meanwhile, back at the coast, the marine layer will take a beating much like it did this morning with that easterly flow aloft and disruptive mid- level clouds. There will continue to be coastal clouds nights and mornings, but more patchy and intermittent. Daytime temperatures will not change much, but will slightly increase next week, particularly at the coast, with the monsoon flow diminishing the marine layer. Higher nighttime lows might be more noticeable as we get more clouds and humidity on top of those summerlike sea surface temperatures now in the 70s. Max temps will be within a couple degrees of normal, but min temps will be a few degrees above normal. && .AVIATION... 170330Z...Coast/Valleys...Low clouds increasing in coverage at the coast will spread inland after 06z, reaching up to 15 miles inland by 14Z. Bases will be 1200-1800 ft MSL and cig impacts are expected at coastal TAF sites. Clearing to the coast likely 15-17Z. Mountains/Deserts...FEW-SCT clouds AOA 12000 ft MSL with unrestricted vis through Saturday. && .MARINE... No hazardous marine conditions are expected through Wednesday. && .FIRE WEATHER... Increasing monsoonal moisture Saturday and Sunday will bring a chance of showers and thunderstorms to the mountains. While only a few storms are expected, a few could bring wetting rains while others could bring dry lightning. Isolated sprinkles or light showers are expected late Saturday through Sunday morning, but no lightning. Sunday afternoon there will be a higher chance of thunderstorms, but accompanied by wetting rains. Each afternoon Monday through Friday there is a chance of at least isolated thunderstorms, with a greater chance Wednesday and Thursday leading to increasing chances for wetting rains while decreasing chances for dry lightning. && .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...Gregoria (Update)/MM (Previous Discussion) AVIATION/MARINE...PG
The Santa Ana Mts radar (KSOX), 88 km away, was scanning. The volume nearest the first event began at 08:03 UTC.
1 debris flow, 1 lightning, 1 heavy rain. Local standard time, as filed.
San Bernardino County Public Works reported the clearing of debris and barricading as needed at Big Bear Yard (Elv. 6815 ft).
Retransmit. FOX5 reported 2 palm trees (with photos) on fire from lightning strike. 15 cloud to ground strikes detected from 4 am to 530 am in Vista and 95 total in San Diego county and open waters. Fire burned for 20 minutes until fire agency put out. Unconfirmed report of another palm tree burned in Oceanside. Damage cost is estimated.
Heavy rain from monsoonal thunderstorms with 1.60 inches of rain measured at Big Bear City Station, 0.29 inches of which fell in 5 minutes from 6:10 PM until 6:15 PM.
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, July 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: 973219, 973217, 973215.