The topography of region’s rain
Geography plays a big part in precipitation totals. But sometimes it’s just the heat.
Meteorologists call it the “Elsinore convergence,” and over the last three days, it’s been bringing extreme weather to a large swath of inland Southern California.
Soaked in moisture from Tropical Storm Linda and driven by Southern California’s typical onshore breeze, gusts of air are divided by and wrap around the Santa Ana mountains. They then collide head-on over the Inland Empire and are pushed up by hot air.
Thousands of feet above, the moisture cools, condenses, and forms dense clouds that can dump inches of rain on isolated areas in short, damaging bursts.
Since Tuesday, Inland Empire residents have been seeing that convergence in action. Roads have washed out, cars and people have been swept away in floods and lightning bolts — created by the instability of the hot air — have ignited small brush fires and knocked out power to thousands.
The line of the convergence can be drawn almost directly from Lake Elsinore to Beaumont, said National Weather Service forecaster Miguel Miller.
Residents in Corona and Temecula on either side of the Santa Ana mountains can attest to the wind while folks in Moreno Valley see what happens when the gusts collide.
When the breeze pushes the air up against the San Bernardino and San Jacinto mountains, the air is again driven up, like it is in the hot valleys, and any moisture left is wrung out over areas like Forest Falls.
Months ago, the Forest Falls area was inundated with record-breaking rainfall from Tropical Storm Dolores that flooded the town.
But residents in Los Angeles County’s high deserts can’t blame the topography so much for the rain they’ve gotten during this week’s heat wave, said weather specialist Stuart Seto. It actually is just because it’s so hot in the desert that they’ve been getting rain.
When Tropical Storm Linda’s moisture passes over the Angeles National Forest, it meets the heat on the other side and is pushed up where it cools, condenses and rains.
“There’s so much heat, lots of unstable air there, that helps lift the air up and generates thunderstorms,” Seto said.
But come wintertime, the story is different, Seto said. The air hits the mountains and hills outlining the Grapevine, where it’s driven up and creates the rain that causes the mudslides over fire-scarred terrain.