Parts of Sierra Madre near the burn scars of the Eaton Fire are under evacuation warning through at least Friday morning, including neighborhoods north of East Grandview Avenue. (You can check your evacuation status via Genasys Protect.)
With little vegetation left to hold the mountainsides up, the danger is that mudflows could overfill debris basins with any significant rain, said Sierra Madre Fire Chief Brent Bartlett. Debris basins are still full of mud, trees and ash from the most recent storm.
" When the February storm hit, all of our debris basins were empty. That is not the case this time," Bartlett said.
Sierra Madre has eight debris basins that protect neighborhoods downstream from flooding and mudflows. All of those were filled to capacity during last month's storm, Bartlett said. At least one dam that sits above the canyon neighborhood in the northeast part of the city overflowed during the February storm, causing damaging mudflows in that area.
"While county and city contractors have been working tirelessly to clear [the debris basins], we are not starting from empty," Bartlett said. "This means that any significant rainfall could lead to severe flooding, mudflows and debris flows."
County and city crews have been working around the clock to clear debris basins -- the county manages 19 from Altadena to Arcadia.
Up to two inches of rain is expected across the L.A. region in this storm, but areas especially in the foothills could see bursts of rain that amount to more than that, and possibly trigger dangerous mudflows. A rate of rainfall that's half an inch per hour or more is likely to trigger mudflows.
"These conditions are dangerous and unpredictable," Bartlett emphasized.
So if you're under evacuation warning, you should pack a go bag for at least a few days and be ready to go immediately if an evacuation order is issued.
Sierra Madre residents can pick up sandbags at City Hall.