Valley News -

By Alex Groves
Associate Editor 

Long-awaited 'atmospheric river' storm fizzles in Southwest Riverside County

 

Last updated 3/22/2018 at 4:28pm

Alex Groves

Dark and foreboding clouds linger over the Morgan Hill neighborhood near Temecula on Thursday, March 22, 2018.

A powerful "atmospheric river" storm that moved in over the region from the Pacific Ocean delivered heavy rain that caused rock slides and shuttered roads in San Bernardino County, but the same storm fizzled in Southwest Riverside County, delivering only a small amount of rain by Thursday afternoon.

"So far, most locations in and around the Temecula area have gotten anywhere from two-tenths of an inch to about a quarter of an inch," said Philip Gonsalves, a National Weather Service meteorologist.

Gonsalves said that rainfall amount would likely double by Friday morning, meaning most areas from Lake Elsinore to Temecula will have seen about a half an inch altogether. That's a lot less than the estimated 1 to 7 inches the National Weather Service had initially anticipated.

Some areas, such as locations in northern San Bernardino County, got closer to what was anticipated, seeing somewhere between 1 and 1.5 inches of rain, with still more to come.

The storm brought flooding along a portion of the Cajon Pass and a Rockslide on State Route 18 between Snow Valley Mountain Resort and Big Bear Lake.

So what made the difference in terms of rainfall? Topography, according to Gonsalves.

He said the northern portion of San Bernardino County is much more mountainous whereas the land in Southwest Riverside County tends to be flatter.

Alex Groves

Old Town Temecula got a soaking from an atmospheric river storm on Thursday, March 22.

"Once the topography starts to become hilly or mountainous, that's what we refer to as an 'orographic effect'," Gonsalves said. "That's where low-level winds push the moisture against the slopes of the mountain, it goes up, and that creates a mechanism for extracting the moisture."

Gonsalves said the storm wasn't any more impressive than any of the others that came before it this month.

"There was more moisture in the atmosphere with this storm than with some of the others but we didn't have an efficient enough mechanism to cause that water, that moisture, to precipitate out of the atmosphere as rainfall," he said. "Otherwise we would have gotten, on the whole, significantly more than we are seeing."

This is a breaking news story and will be updated.

 

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