By Jim Purpura. Posted July 29, 2012, 7:47 PM.

Meteorologists in this area are aware of a local weather effect in the Inland Empire called the Elsinore Convergence Zone. I thought WeatherCurrents' readers might be interested in what that is and why it is so beneficial to the Southwest Riverside County area.

Air arriving in Temecula, Murrieta, Wildomar, and Menifee from the Pacific Ocean cannot make it here from all westerly directions because of the significant barrier the Santa Ana Mountains pose. Instead, marine air travels into the area through a low spot in the mountains, the Rainbow Pass. (This is just about where the Border Patrol station is on I-15.) Since the pass is about 1,400 feet or so elevation, on days where the marine layer is under that depth, it doesn't make it into Southwest Riverside County, and we end up having very warm, dry conditions along with low humidity.

But, when the marine layer is deeper than the pass, the cool air spills in over the gap and moves north and east across Southwest Riverside County.

Likewise, across northern portions of the Inland Empire like Ontario and Riverside, Pacific air traverses coastal areas in Los Angeles and Orange County, then moves east and southeast along the Santa Ana Canyon, where state route 91 is.

As a result, the northwest winds in the northern portion of the Inland Empire converge (meet) with the southwest winds from the south part of the Inland Empire. The usual meeting place where these winds converge is a line near Lake Elsinore that extends east across Sun City and Perris and on to the San Jacinto Valley. The winds can come together a bit further north or south on any given day. This meeting of winds is called the Elsinore Convergence Zone.

You can often see the effects of the Elsinore Convergence Zone. If you're in the Southwest Riverside area and look to the north you can often see the Santa Ana mountains disappear into the north (smoggier) portion of the zone. Notice on many days as you drive south from Corona on the 15, how sunny but hazy it is. As you emerge from the hills north of Lake Elsinore, right around the Outlet Mall. The sky suddenly goes from milky white to deep blue.

Sometimes in the summer the Elsinore Convergence Zone is visible as a line of cumulus extending east to west as looking north from Temecula.

Soaring (glider) enthusiasts use the zone for soaring. The greatest lift is on the north side of the zone. On days where summer thunderstorms form in the San Jacinto Mountains and move west into the valley, these storms tend to move west along the Elsinore Convergence Zone.

So it is the Elsinore Convergence Zone we have to thank for keeping the air clean in the south part of the county. Thanks to it, Temecula, Murrieta, Wildomar, and parts of Menifee usually get clean ocean air from around Camp Pendleton, instead of polluted air from the Los Angeles basin.