In my "Desert Studies" column I try to tie the topics into current events and concerns. Such was the last installment regarding possible flood threats on the Mojave River. But there is another potential flooding threat on the Mojave Desert. It's called "monsoonal" thundershowers, and is prevalent during the summer months.

A monsoon is a meteorological term and in its simplest definition, is simply a reversal of wind direction. And it's not present here alone by any means. The monsoon season in South and Southeast Asia, especially India and neighboring countries, provides most of those nations annual rainfall. If it fails, and it does, they'll have terrible drought and crop losses that might kill millions of people through starvation. If it's tool severe millions may drown.

Fortunately, our monsoon season is not so critical. Because of our geographical location, our usual wind flow is from west to east or south to north. That's why our prevailing winds are southwest. But during the summer months, especially June to September, a plume of moisture, originating over northern Mexico, works its way over the Southwest. Even states as far east as Texas (from our perspective) experience the monsoon. The plume of moisture usually extends northward in Arizona, New Mexico and Utah. But gradually the "reversal" of wind direction, not from west to east, but rather from east to west, pushes the moisture over Southern California and occasionally even further north.

The result is building thunderheads (cumulonimbus clouds) over our eastern and southeastern mountains, especially the eastern San Bernardino ranges. The build-up is usually gradual, taking days or even weeks to become strong enough. But eventually it "spills" over the mountains and descends onto the High Desert.

I always tell people to "beware the east wind" in a building thunderstorm. For the sheer force of the monsoon's east-to-west flow pushes an east wind ahead of it, usually carrying the scent of rain and wet vegetation. In particular, the greasewood bushes, which, when wet, produce a distinct scent on their own. You can literately "smell" the rain coming.

Then beware of the thunder, and particularly the lighting. Lightning, especially cloud-to-ground discharges (called chain lighting) can reach for miles. People fifty miles away from a thunderstorm, and with clear skies overhead, have been struck and killed by lightning. Lightning produces thunder, not the other way around. A general rule on thunder is that for every five second delay, the lightning is a mile from your location. I like to watch a thunderstorm, but when the count runs under five seconds I run for cover.

"Dry lightning," that is, a thunderstorm without rain, is especially dangerous. Without rain to dampen the ground and vegetation, it can easily start brush fires. Three times, I've seen our own Ord Mountain, which backs the Marianna's, burn from end to end. In fact, it's the only mountain I've ever seen that burns sideways.

Usually the rain precedes the thunderstorm and then intensifies as it grown nearer. The violent updrafts and downdrafts commonly present in a thunderhead can produce heavy rain of flash flood proportions, golf ball size hail capable of shattering windshields and other damage, and tremendous blasts of wind, and even tornadoes.

So pay heed to the five second rule and the east wind during a threatening thunderstorm. Enjoy the show but don't let it harm you!