It’s a pretty straightforward forecast…mostly sunny skies with mid-summer (plus) temperatures through the next week. Saturday will continue the dry and stable pattern with valley temperatures reaching the 90s. Sunday could bring an isolated mountain thunderstorm south of Lake Tahoe in the Sierra, and a few afternoon clouds could drift into the region as a result. Temperatures peak on Tuesday at somewhere around 100 degrees.

water cycle1

So how do you get water out of the ocean into the clouds? It’s all part of the water cycle. While we know that water (liquid) falls from the skies out of clouds, how does it get up there to begin with? Let’s start with liquid water in the ocean. On a molecular level, water can’t be transported into the air unless it turns into vapor, which is essentially the release of individual water molecules to float free in the atmosphere. If you heat liquid water, you increase the rate those water vapor molecules break away from the liquid ones. But clouds aren’t made up of water vapor. Water vapor is invisible… clouds aren’t. So in order to turn the water vapor back into liquid, you have to cool it. That’s the condensation part of the water cycle. But how do you cool water vapor in nature?

cloud condensation

The laws of physics state that if you reduce the pressure of a gas, it will get colder. The most natural way to reduce the pressure of a gas (air) is to take a chunk of it from a lower elevation and raise it to a higher one. As you probably already know, as you go up in elevation, the air pressure drops. That’s why your ears pop as you drive over the mountains. So if you lift air upward, it will expand and cool. With more lifting, more condensation occurs, and the little itty-bitty drops that make up a cloud and can remain suspended in the air currents become too large and heavy to stay up there, and you get rain.

I realize this may seem elementary to many of you, but it is a simple way of saying rising air means a chance of rain, while falling air equates with sunshine.