WEATHER CORNER

Kid's questions

BY JAN NULL
Special to the Mercury News

This week's questions are a sampling of more than 100 excellent questions from second-, third- and fourth-grade science students at South Valley Cardin School in San Jose. Their teacher, Emil Kissel, incorporates weather into many of his classes. He has students study, measure and even
forecast the weather.

Q. Why does lightning come before thunder? Christopher - Second grade
Q. Can you have thunder without lightning? Ben - Second grade

A.  It's the lightning that causes the thunder, but they occur nearly simultaneously. Thunder is created when a very hot lightning stroke heats the air to about 50,000 degrees. This causes the air to expand very rapidly, and the shock wave of this expanding air is what we hear as thunder. It's very much like blowing into a paper bag, sealing it and then popping it; the resulting noise is also caused by the sudden expansion of air.

Consequently, if you are very close to a lightning strike, you will see, hear and feel the lightning and thunder about the same time. However, if you are some distance away, you will see the lightning before you hear the thunder.

Q. Does it rain in Arizona? Annalise - Second grade

A. Absolutely, and in some places as much or more than San Jose's 14.5 inches per year. For example, Phoenix gets 7.66 inches, Tucson 12 inches and Flagstaff 22.80 inches per year. However, while San Jose gets more than 80 percent of its rainfall from November through April, Arizona can be quite wet in the summer. This is because of a weather phenomenon known as the Arizona or Southwest monsoon. This seasonal shift of winds brings moisture-laden air north from Mexico, resulting in thunderstorms over Arizona during July and August. This is especially noticeable in Tucson, where 2.37 and 2.19 inches fall in the average July and August, respectively. Compare this to San Jose's December average of 2.32 inches.

Q. Why does the sun have a ring around it as a sign that it is going to rain? Katie K.- Second grade

A. A ring around the sun or moon occurs when light is bent by ice crystals in thin cirrus clouds more than 25,000 feet above the ground. These types of clouds often precede the fronts that bring rain to the Bay Area. So yes, rings can be a sign that it will rain, but they can also happen at other times.

Q. What is acid rain? Katie A. - Third grade
Q. If acid rain had more acid in it, could it melt through the glass of a car? James - Third grade
Q. If acid rain can hurt statues, could it ever harm people or animals? Marcy - Third grade

A. Acid rain results when air pollution is carried to the ground by rain or some other form of precipitation such as drizzle or snow. First, winds carry pollutants -- oxides of sulfur and nitrogen -- from industrial areas into the clouds. This is especially true of the coal-burning areas in the eastern United States. The complex interaction of these particles with sunlight and water vapor can create sulfuric acid and nitric acid. The very small acid droplets slowly settle toward Earth. On the way down, they can adhere to cloud droplets and become either acid fog or acid rain.

Acidity is measured on the pH scale of zero through 14, in which zero is very acid, 7 is neutral and 14 is very alkaline. Normal precipitation is typically slightly acidic, with a pH of about 6. However, in the northeastern United States, rainfall sometimes has a pH between 4 and 4.5. Automobile exhaust and the unique characteristics of the Los Angeles Basin's stagnant air have resulted in pH readings as low as 3, or about the same as vinegar! But it would take acid much stronger than that to melt through a windshield.

Prolonged exposure to acid rain or fog can certainly have harmful effects on humans, especially those with pre-existing respiratory problems. Unlike statues, most people get in out of the rain and fog. However, during a particularly bad five-day acid fog episode in London in 1952, more than 450 people died.

Q. Is it possible that if the climate gets too cold, it will snow in San Jose?   Aneesh - Third grade

A. I am going to assume you mean to ask if the weather can get cold enough for snow. The term ``climate'' refers to the weather over very long periods, while weather is what we experience daily. But yes, it can get cold enough to snow at sea level in the Bay Area. It is a fairly rare occurrence, about once every 10 or 20 years. And even when snow does occur, it is usually very short-lived. The last significant snow at the
lower elevations of the Bay Area was on Feb. 5, 1976.

Q. How do you know what the weather is going to be? Laurin - Third grade

A. When meteorologists make a forecast, they look at lots of different information. First we look at what is happening right now by looking at weather reports from the ground, airplanes, ships and weather balloons. We also look at satellite pictures and radar to see what is going on around us right then. Next we look at the computer models. These are simulations of the atmosphere and what it will look like for the next few days.
There are a number of different models, and one of the most important things a meteorologist does is use his or her experience to choose the one that will do the best job of predicting the weather in a given situation.

Jan Null, founder of Golden Gate Weather Services and Adjunct Professor at San Francisco State University, is a retired lead forecaster with the National Weather Service. Send questions to him c/o WeatherCorner, San Jose Mercury News, 750 Ridder Park Drive, San Jose, Calif. 95190. You also can telephone questions at (510) 657-2246, fax them to (510) 315-3015 or e-mail them to weathercorner@ggweather.com.