Moisture and lift. That's really all it takes to have a sudden cloudburst like the one Studio City experienced Thursday afternoon. We usually see this type of storm cell pop up out in the desert, but occasionally some moisture does sneak it's way into the Valley and we get wet in the summertime.
In this case, all the ingredients came together. The storm that affected us here in Studio City was actually triggered by stronger storms out in the Inland Empire. As those storms collapsed, the cold air near the tops of the storms came rushing to earth, pushing air out in all directions. This "outflow" from several strong storms further east interacted with moisture in place over the San Fernando Valley, San Gabriel Valley, and LA Basin, and presto. Thunderstorms.
Thunderstorms begin with some kind of lifting mechanism causing moisture to rise into the cool upper atmosphere, where it condenses. This can be caused by warm air rising or even air being forced up a mountainside. When the lift is no longer strong enough to keep that condensed moisture aloft, it falls to the earth as rain. The stronger the lift, the more moisture accumulates aloft, and the heavier the rain.
At the same time, the warm air rising into the upper atmosphere cools suddenly and descends again. This process, called convection, often creates unbalanced electrical charges and we get lightning, thunder, and all the other theatrics that go along with thunderstorms. Sometimes this convective process can tilt into a horizontal rotation, which can produce the more dangerous mesocyclones and tornadoes, but that doesn't often happen here in the Southland.
The relatively small storm today dumped about a little over a tenth of an inch of rain in about 20 minutes. To put that in perspective, a tenth of an inch is what most weather systems produce in their entirety during the wet season. So while not very impressive by Oklahoma standards, that was still a lot of water in not-so-short a time.
So we'll call it 0.13 inches of rain today, really our first significant rainfall of the new rain season, which began on July 1st. As a weather enthusiast I can't help but hope this is a sign of things to come this winter. All signs point to El Niño developing sometime in September or October, in which case this is just the beginning.