| Published Tuesday, July 18, 2000 in the San Jose
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
Q. Why does the sun have a ring around it as a sign that it is going to rain? Katie K.-
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 -
Q. If acid rain can hurt statues, could it ever harm people or animals? Marcy - Third
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 email@example.com.