Thursday, October 23, 2008

shades of red

Skycrane west of Porter Ranch last week.

By Guy McCarthy

SAN BERNARDINO - The National Weather Service has extended red flag warnings through Saturday night across much of Southern California due to expected low humidity and critical fire weather conditions.

Santa Ana winds have slacked off considerably, but the continued spell of dry heat should remain a concern to fire crews and residents, according to Weather Service updates this afternoon.

Areas noted by the Weather Service include the San Gabriel Valley, the Santa Monica Mountains, the Santa Clarita Valley, and the Angeles, Cleveland and San Bernardino national forests.

Red flag warnings from the Weather Service today mean "that critical fire weather conditions are occurring. A combination of low relative humidity . . . very warm temperatures . . . and critical fuels will create explosive fire growth potential."

The Weather Service warnings are not to be confused with a new system of colored flag warnings devised in the foothill city of Sierra Madre, where officials are also concerned about the potential for devastating post-fire debris flows.

In Sierra Madre, a red flag means go - leave immediately - according to a new warning system announced this week. The Sierra Madre system also includes green and yellow flags.

Red flags won't come out until heavy rains are expected on burned watersheds from the Santa Anita Fire in April and May 2008, said city spokeswoman Elisa Weaver.

But Sierra Madre officials aren't taking any chances with the post-fire situation, Weaver said.

"Our biggest challenge at this point is making sure people understand," Weaver said in a phone interview. "The fires were burning right in people's back yards. We're based right up against these hills."

In Southern California, a steady rain on recently burned slopes can unleash tons of ash and destabilized soil. Depending on rain intensity, the size of the watershed and grade of the slopes, a post-fire debris flow can ooze along at 5 mph or reach freeway speeds - and in either case they can be deadly.

Post-fire debris flows killed 16 people in canyons north of San Bernardino on Christmas 2003.

Some Sierra Madre officials remember a post-fire debris flow that killed two in Bailey Canyon, several months after the devastating Kinneloa Fire of October 1993.

"We don't want to scare people," Weaver said. "We just want them to be aware of the possibilities and to be ready to evacuate when necessary."

A public meeting is scheduled to address the new warning system in early November.

More information is available at the city of Sierra Madre's site.


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