Heavy rainfall triggers mudslides in SoCal on heels of Kay
Tropical Storm Kay dissipated on Saturday but its impacts lingered as the system's remaining moisture mixed with high temperatures to create astonishing scenes like this debris flow.
After a brush with Tropical Storm Kay over the weekend, parts of the southwestern U.S. got even more rain on Sept. 12, leading to dangerous mudslides in some areas.
Floodwaters and mudslides swept through portions of Southern California on the heels of Tropical Storm Kay on Monday, triggering immediate evacuation orders for parts of the Inland Empire.
Flash flood warnings were issued Monday following heavy rainfall from the night before across San Bernardino County, including Oak Glen, where one Twitter user caught video of an enormous flow of flash-flood debris suddenly overtaking a neighborhood street.
"If I had been 2 min[utes] earlier...," Dr. Roger Seheult posted along with the video. He explained in a second post that the debris had come from the burn scars of the El Dorado wildfire, which had destroyed some 22,000 acres in the Yucaipa area in the fall of 2020. Investigators had determined the fire had ignited from a pyrotechnic device at a gender reveal party.
An extended version of Seheult's original video showed a man watching another round of debris come charging down the road before he quickly turned and ran for cover.
"Get out of here!" the man seems to be saying as the sound of the surging debris muffles his words.
The Yucaipa Police ordered residents to evacuate Monday from several communities, including Oak Glen.
Waves of mud started barreling down the mountain in Oak Glen, California, on the afternoon of Sept. 12, following heavy rain in the area from Tropical Storm Kay.
Tropical Storm Kay, which was eventually downgraded to a tropical rainstorm on Saturday, unleashed intense winds and flooding rains.
"Moisture and leftover energy from the former Kay was able to combine with the heating of the day to cause thunderstorms to develop," AccuWeather Senior Meteorologist Dave Houk said. "The leftover tropical moisture fueled the heavy downpours."
While Kay provided some relief from the prolonged heat wave across Southern California, "cooler" temperatures for the region simply meant that temperatures dropped below the 90s.
San Bernardino, the capital city of the county of San Bernardino, had been in the throes of the heat wave up until Saturday when temperatures dropped to the mid-80s. While the heat rebounded into the 90s on Sunday, temperatures have since remained in the 80s, according to AccuWeather data.
Temperatures have cooled a bit more for Oak Glen following the additional rainfall, with the high temperature from Friday dropping by roughly 10 degrees Saturday as Kay's rainfall closed in on the area. The heat rebounded slightly over the weekend, however.
"Not everyone saw the storms, but where they hit, they were capable of bringing rainfall rates as high as 2 inches per hour," Houk said.
Debris, mud and rocks blocked a portion of State Route 38 on Monday following multiple mudslides and rockfalls. (Twitter/@Caltrans8)
In addition to the sudden debris flow in Oak Glen, the burst of rainfall triggered a handful of mudslides that crashed down the mountain slopes and blocked off stretches of interstate.
A portion of the east and westbound lanes of State Route 38 between Lakewood Drive and Jenks Lake West was closed Monday afternoon following multiple mudslides and rockfalls in the area, according to the California Department of Transportation (Caltrans). The route remained closed as of early Tuesday morning.
The northbound lane of State Route 18 also was closed early Tuesday following a mudslide, but all lanes on the route later reopened.
Debris, mud and rocks blocked a portion of State Route 38 on Monday following multiple mudslides and rockfalls. (Twitter/@Caltrans8)
The city of Riverside in Riverside County, part of the Inland Empire, received 0.78 of an inch of rainfall, according to the National Weather Service (NWS). One of the highest totals reported from the storm was 1.45 inches at Wrightwood, in the San Gabriel Mountains of San Bernardino County.
Big Bear in San Bernardino County saw record-high daily precipitation on Monday, with 0.20 of an inch of rainfall, beating the record of 0.04 of an inch set in 1975. In Thermal, located in Riverside County, a record-breaking 0.01 of an inch of rainfall was just enough to beat out the trace amount recorded in 2012.
"In general, the thunderstorms brought the rain in a relatively short period of time," Houk said. "When the rain comes down hard in those areas, the dry ground and terrain allow for quick runoff of water instead of rain that gradually soaks into the ground."
Tuesday will be the last day the pattern will linger in the area, with deeper moisture being pushed eastward Wednesday through the end of the week as winds aloft from the west send in dry air, according to Houk.
"The jet stream sinking southward and onshore flow at the surface will also keep daytime temperatures below average after the first week of this month was unusually hot," he said. "Low clouds and patchy fog can make an appearance for a couple of hours late each night and morning in the Inland Empire, but the more widespread night and morning clouds will be back closer to the coast."
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