Weather Corner (01/27/04)

You are at your child's soccer game and there are threatening clouds. When will the rain start?

Or you're headed to the airport and want to know the latest weather at your destination and whether your flight will be delayed.

Now you can get all this and more by flipping open your cell phone.

Meteorologists love gadgets, especially the latest and greatest weather-related ones. At the recent American Meteorological Society annual meeting in Seattle, there were lots of goodies for the 3,000 attendees, but Wireless Weather from WeatherNews Inc. of San Francisco was one of the standouts. I even like it enough to pay for it!

Taking advantage of the latest generation of phones that can receive data and are programmable, WNI delivers weather conditions, a seven-day forecast, the latest radar image, sunrise/sunset times and any advisories from the National Weather Service for more than 30,000 locations worldwide. Already being used on more than a million phones worldwide, it's now available in the United States from AT&T, Sprint, Verizon and Alltel for less than $4 a month.

Your phone can be programmed to wake you with the latest weather conditions or to go to the forecasts for your five favorite cities. You can find out whether there are delays at your airport and even the phone numbers for most airlines if you need to change your reservations. There's also travel weather with climate information that will show the average maximum July temperature in, say, Tierra del Fuego (38 degrees F). Despite the small amount of screen space available, the images are clear and the navigation between screens is intuitive.

For more information, see www.weathernow.com.

Q I've always wondered how sea level is measured. There are so many variables, given the weather, tides, geology, temperature, etc. Can you shed any light on the subject? Jim Hatfield - Santa Cruz

A A variety of tide gauges are used. Two of the more common types are floats that rise and fall with the water and bubblers that release nitrogen bubbles at different rates depending on the height of the water.

These measurements are averaged hourly over a 19-year period to determine mean sea level. This 19-year period is called a National Tidal Data Epoch and is used because of the 18.6-year lunar cycle. The most current NTDE is from 1983 to 2001.

Q We live in the Santa Cruz Mountains, behind Los Gatos, and we get a lot of rain. My wife has a question about how TV weather folks report the amount of rain we have had. When they speak of rainfall, do they refer to the period from Jan. 1 to Dec. 31? Or do they consider the rainy season to start sometime near October and go through Sept. 30? Michael Robinson - Los Gatos

A Meteorologists in the western United States use a July 1 to June 30 rainfall season. This is a logical place to separate seasons because of the natural summer ``drought'' we experience in the West every year. In other parts of the country, where a significant amount of the annual precipitation falls in the form of summertime thunderstorms, meteorologists use the January through December calendar year.

To further confuse the issue, hydrologists, who study surface and groundwater, define a ``water year'' that begins Oct. 1 and ends Sept. 30. Since most of the West gets very little rain from July through September, data for their water year closely matches our rainfall season.

Q What is the chemical composition of snow, if it is not simply H2O? And what are some common impurities in snow? Susan Letcher - Sonoma

A If it were totally pure, there would be less of it. A key element to the development of snow is condensation nuclei. These are tiny particles, about 1/10,000th the size of a raindrop, upon which water collects and grows into a size large enough to fall from the sky.

Common condensation nuclei are dust, volcanic particles, smoke from factories and forest fires, ocean salt and sulfate particles from phytoplankton in the ocean.

While the concentration of nuclei is very small, snow can become more polluted as it falls through atmosphere. In industrial areas it can mix with sulfur dioxides from factories and nitrogen oxides from vehicles to become ``acid snow.''

A substance is considered neutral if it has a pH of 7.0 and acidic if the value is less than 7. Due to carbon dioxide in the air, most precipitation is slightly acidic, but if the pH is less than 5.0 it is considered acid rain or snow. Some snow downwind of large industrial sources has had pHs of about 3.0. For comparison, vinegar has a pH of about 2.2.