Published Tuesday, December 3, 2002 in the San Jose Mercury News

Weather Corner

Holiday book for those who are watching the weather

Special to the Mercury News

Does a weather watcher in your house have questions about El Niņo? Bay Area summer fog? The difference between cirrus and cumulus clouds?

Look no further than your local bookstore or online book source to find some great gift ideas. Here are some of my favorites:

With El Niņo back in the news, look for ``Currents of Change'' by Michael Glantz. The book does an excellent job of discussing not only the science of El Niņo but also its impact both locally and globally.

``Weather of the San Francisco Bay Region'' is an excellent primer on local weather patterns, by Harold Gilliam.

If you're looking for a fictional twist on local weather, my all-time favorite weather novel is ``Storm'' by George R. Stewart. Even though ``Storm'' was written in 1941, it still captures the multifaceted impact of a fierce winter storm as it matures over the Pacific and slams into the Golden State. It was the genesis for giving names to storms. Even though it is out of print, I frequently run across copies from used book dealers.

A great choice for a general interest meteorology book that has something for the layman and a more experienced weather watcher is ``Weather for Dummies'' by John Cox. This book, from the familiar yellow cover, does a good job of explaining the basics of weather and climate without dumbing things down too much.

Two more-advanced meteorology textbooks are ``Essentials of Meteorology'' and ``Meteorology Today'' by C. Donald Ahrens. The former, a softcover primer in its third edition, is one that I have used as a text for university courses.

The just-released seventh edition of ``Meteorology Today'' is the premier weather text in the nation.

The ``Glossary of Weather and Climate,'' published by the American Meteorological Society, is another nice addition to the weather library. It has more than 3,000 definitions that cover not only weather but also climate, oceanography and hydrology. It's available online or from the AMS.

Q I have noticed that the ``fall streaks'' from cirrus clouds over Tracy have consistently blown to the west during the fall. This indicates upper-level easterly winds. Yet, my meteorology text states that these winds should consistently be westerlies. What am I missing? Is it perhaps possible for there to be upper-level layers of winds flowing in opposite directions? Could this be an optical illusion? Is the cloud being blown to the east while the fall streak is remaining stationary, or at least traveling at a slower speed than the cloud, thus giving the impression that the fall streak is being blown west? James Miner -  

A Fall streaks are the wisps that can sometimes be seen falling below high, thin cirrus clouds. They are ice crystals that fall out of the cloud but evaporate as they fall into drier air below. Fall streaks are analogous to another phenomenon known as ``virga,'' which is rain falling from lower clouds and evaporating before it reaches the ground.

As the fall streak drops, it often is falling into air that is moving slower than its ``parent cloud,'' which is moving toward the east. Thus, while it appears to be moving to the west, it is in fact just moving east at a slower pace.

Q Recently I moved to Southern California from Colorado, and hearing the term ``marine layer'' in weather reports sounded odd to me. I have been chastised repeatedly because of my insistence that this is just another word for fog, and that calling it a marine layer is like calling a trashman a ``waste disposal engineer.'' Are fog and marine layer synonyms or are the properties of each different enough to warrant a separate name? Philip Thomas -  
Aliso Viejo

A They are not synonymous. The marine layer can be in the form of fog, low stratus clouds or just cool, moist air that moves inland from the sea. But fog does not necessarily have to be the result of the marine layer. It can come about by radiational cooling of the ground, which in turn causes moist air next to the ground to condense in visible water droplets. And stratus clouds do not necessarily have to be the result of the marine layer. Finally, fog is any condensed water vapor or cloud that comes into contact with the earth's surface, regardless of where the vapor originates.

Q Question: What is cloud seeding? Jennifer Menicucci - Cloverdale

A First, the seeding of clouds does not really ``cause'' precipitation. Instead, it enhances the processes already occurring in a cloud by the introduction of tiny particles upon which rain or snow can condense. Originally, dry ice (frozen carbon dioxide) was used, but the chemical of choice is now silver dioxide.

Under the best conditions, it is estimated that a maximum increase in precipitation of 10 percent can be achieved through seeding, though seldom are ideal conditions present, and the actual yields are considerably less. As you would expect, of course, it is extremely difficult to determine how much precipitation might occur naturally, which makes it impossible to tell the precise effects of cloud-seeding.

Q I am new to the Fresno area. What is ``tooley'' fog, and where did the expression come from? Elizabeth MacDonell - Riverdale

A The fog you are talking about is ``tule'' fog and is named for the tule reeds that are prevalent in the marshy areas of the Central Valley. These same areas are also ideal for the formation of the thick, low-lying fog that develops on cool, clear winter mornings.

Tule fog typically forms on the first or second clear night after it has rained, when skies have cleared and winds are light. This happens when high pressure returns, creating an inversion with colder air near the earth's surface than aloft. This, in turn, causes moisture on the ground to condense into a low-lying layer of fog that develops from the ground up. Because the coldest air settles into the lowest elevations, such as along a river or stream, this is where fog is most likely.

Jan Null, founder of Golden Gate Weather Services, 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, e-mail them to or fill out a form online at Please indicate in your e-mail what city you live in.