Where do rain, snow and clouds come from? PG&E meterologist explains

Many fifth-grade classes in our local school district are learning about weather in their science curriculum. Consequently, I’ve had the honor of visiting a few of our local elementary schools and assist our esteem fifth-grade instructors in teaching the fundamentals of our atmosphere.

We used real-life, hold-in-your-hand experiments: A weather balloon launch to explain the five layers of the atmosphere and upper-level winds. A cloud in the bottle, fire cylinders, and my favorite, the lightning-fast crush can experiment.

All are designed to teach about air pressure and the water cycle.

The water cycle is intriguing. A single drop of rain, or at least one of its 1.67 sextillion water molecules of H2O, has more than likely been on an incredible journey over countless millenniums.

It may have existed in us, perhaps a dinosaur, the glaciers that carved out the Great Lakes or Yosemite, an ancient redwood, or, more recently, the water that forms when liquid hydrogen reacts explosively with liquid oxygen in rockets launched from Vandenberg Air Force Base.

As a solid, it may have been locked in ice sheets, glaciers, icebergs, snow or even hail.

Of all the liquids that exist in temperature between 0 to 100 degrees Celsius, water is the only one that expands when it freezes.

If water decrease in size when it froze, life on Earth may not exist. In other words, Earth would become a giant ice ball, reflecting much of the sun’s energy back into space.

In its liquid state, water covers about 71% of the Earth’s surface. Nearly all this water is contained in the oceans. Only 2.5% of this liquid is freshwater.

As a gas, H2O makes up between 0 and 4% of the atmosphere; most of the time in California, it’s less than 1% as water vapor in our sky. About 90% of the water vapor in our atmosphere comes from evaporation from the oceans or lakes.

The sun provides the heat and helps to generate the winds that evaporate millions of tons of water from the oceans into the air each day. The winds and heat also evaporate water from rivers and streams.

Evaporation is a cooling process in which water in its liquid stage state is converted into vapor. Believe me, if you ever wear wet clothes on a breezy day, you would understand that it is a cooling process.

A fantastic amount of water transpires from the leaves of plants. A single large oak tree in our county can move 100 gallons or more of water into the air in just one day during the summer, while an acre of corn gives off about 3,000 to 4,000 gallons of water each day.

As this moist air rises, it slowly cools.

When its relative humidity reaches 100%, the invisible water vapor condenses on microscopic nuclei from dust, volcanoes, pollen, forest fires, pollution from cars and factories, salt from ocean spray, or sulfite particles from phytoplankton in the oceans.

Think of a cold glass of iced tea on a warm day. The water vapor condenses on the outside of the glass, producing water droplets.

When enough water vapor condenses on particles in the atmosphere, they produce clouds. Condensation is the opposite of evaporation and consequently is a warming process. A lot of people notice that it gets warmer right before it rains or snows.

When the water vapor changes to a liquid, it releases energy. This is also one of the main driving forces behind hurricanes and the monster mid-latitude Gulf of Alaska storms that so often can bring rain to California.

When the conditions are right, rain, hail, sleet or snow comes falling to the Earth. When this happens, it is called precipitation.

This timeless process of evaporation, condensation and precipitation is called the water cycle.

Diablo Canyon tour

Back by popular demand is the Weather Watchers tour of Diablo Canyon power plant and lands. If you and your family would like to participate in this free tour on Tuesday, please visit tourdcpp.pge.com to register. The deadline to sign up is Monday.

It will start at 9 a.m. at the PG&E Energy Education Center, 6588 Ontario Road in San Luis Obispo, and will finish by noon.

This story was originally published November 24, 2019 at 4:50 AM.