Increased monsoonal moisture in Southern California resulted in thunderstorms, heavy rain, and debris flows across the region, particularly in the mountain areas.
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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.
Increased monsoonal moisture in Southern California resulted in thunderstorms, heavy rain, and debris flows across the region, particularly in the mountain areas.
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 10, 8:30 PM PST, 3 hours 30 minutes earlier.
Area Forecast Discussion National Weather Service San Diego CA 930 PM PDT Tue Jul 10 2018 .SYNOPSIS... Partly cloudy skies will prevail tonight with only a small chance of a thunderstorm over the high deserts of San Bernardino County. Conditions will be more favorable for thunderstorms with locally heavy rain Wednesday afternoon, mainly in the mountains and deserts. The thunderstorm activity will decrease a little each day the rest of the week as high pressure aloft rebuilds over the Southwest, along with higher temperatures in the mountains and deserts. Thunderstorms could increase again early next week. Along the coast, patchy night and morning low clouds and fog will prevail through early next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Only isolated showers and thunderstorms occurred this afternoon due to limited instability, even though moisture was copious, with 1.66 inches of precipitable water in the late afternoon NKX sounding. Except in parts of the high deserts of San Bernardino County, CAPE values, even aloft, were low, so most likely we will have no further convection overnight. Stratus is visible off the coast, and locally along the coast, on the fog product, and that should spread 10-15 miles inland overnight, with an inversion base around 1000 ft MSL. No strong desert winds are expected overnight as the convection in Arizona was less strong this afternoon/evening with less wind, and the wind that occurred was SE versus E, so it wasn't directed towards the Coachella Valley or San Diego County Deserts. There is convection over Sonora, but probably not enough to contribute significantly to any Gulf moisture surge from the southeast into our deserts. Convection should be better over the mountains and adjacent areas Wednesday as there will be fewer debris clouds to hamper the instability. With abundant moisture between 800 and 500 MB, we should have scattered thunderstorms with locally heavy rain, though 00Z NAM and even GFS have back off on precip values slightly from earlier runs, mainly due to lower instability. Local WRF shows the convergence starting out over the mountains at midday and gradually shifting east into the deserts later in the afternoon, so those will be the areas most likely affected by thunderstorms. Confidence is low for anything forming in the Inland Empire as instability looks lower there, and east flow through Banning Pass looks less likely to interact with the south and west flows meeting at the Elsinore Convergence Zone. There is still the possibility of isolated flash flooding, but confidence is not high enough for a flash flood watch. The inverted trough will be over us, but it appears not to have very strong dynamics. The trough will move to the northwest slowly Thu/Fri, and tstorm chances will gradually lower then. The upper high will build over the Interior West but remain to our north, so we will continue to be in east-southeast flow aloft through early next week. Just enough moisture and possibly instability will remain for some chances of mountain tstorms over the weekend, with increasing moisture again early next week. Temperatures will increase again in the deserts later this week due to less cloud cover and the rebuilding upper high, though more onshore flow and a strengthening marine layer will cool coastal areas some, though temps in most areas will be a little above normal Thursday through early next week. && .AVIATION... 110330Z...Coast/Valleys...Scattered mid level clouds around 120000 ft MSL will persist through the period. Very little convective development has occurred today, and development overnight is expected to be restricted to the mountains. Stratus deck with bases 800-1200 ft MSL and tops around 1500 ft MSL will develop along the immediate coast and impact the coastal terminals beginning 04-08Z and lasting until 14-16Z. Isolated SHRA/TSRA could impact the inland valleys Wednesday afternoon with bases 2000-3000 ft MSL. Hazy conditions are likely Wednesday for the inland empire terminals (KONT/KSBD). Mountains/Deserts...Current conditions to the east indicate a lower potential for a haboob or blowing dust across the deserts tonight. Isolated SHRA/TSRA will develop over the mountain areas tonight with a small potential of activity moving into the lower deserts. Will not mention anything in the TAFs due to low confidence. A better potential for thunderstorm development Wednesday with activity likely to develop by midday over the mountains then spread into the deserts during the afternoon. Have placed VCTS in both KPSP/KTRM TAFs after 20Z Wednesday. Expect cloud bases 3000-5000 ft MSL and tops to 40000 FT MSL with this activity. Any storms that form could be accompanied by strong UDDFS and wind shear, brief surface wind gusts 30-40 knots, and restricted visibilities (1-3SM) due to blowing dust or rain. && .MARINE... No hazardous marine weather is expected through Saturday. && .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...Maxwell AVIATION/MARINE...Moreland
The Santa Ana Mts radar (KSOX), 72 km away, was scanning. The volume nearest the first event began at 08:00 UTC.
2 heavy rain, 2 flash flood, 1 debris flow. Local standard time, as filed.
One day total rainfall from Mesonet 7 mi NE of Cherry Valley (yucc1) of 1.84 inches.
Mesonet station (f2736) reported a 24-hour rainfall total of 1.56 inches.
California Highway Patrol reported a mudslide along Highway 18 northeast of Big Bear City that was 6 feet deep and extending 20 feet across the highway. 12 vehicles were stranded in the mudslide. Highway 18 was closed between Big Bear and Lucerne Valley due to the debris flow.
Monsoonal moisture brought thunderstorms to the San Bernardino Mountains on July 12th. This resulted in flash flooding on Highway 18 near mile marker 65 (Mitsubishi Cement Corporation Plant). numerous vehicles stranded due to significant flow of water and debris. Highway 18 was closed in both directions through the afternoon on July 12th.
CalTrans and California Highway Patrol reported flash flooding on Valley of the Falls Drive near Highway 38. Concerns for debris flow movement and heavy rain forced the closure of Valley of the Falls Drive through the afternoon on July 12th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2018Every state in 2018This day in weather historyWarnings in California, July 2018
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: 776672, 776674, 776570, 776576, 776590.