Published Tuesday, March 25, 2003 in the San Jose Mercury News

Weather Corner
El Niņo is just one piece in the weather jigsaw puzzle

Special to the Mercury News

In February 2002, shortly after an El Niņo was forecast for this winter, I wrote a column on California myths about El Niņo. The No. 1 myth was that all El Niņos are the same. It's important to keep in mind that El Niņo is not the only thing happening in the atmosphere; other patterns can enhance or detract from its overall impact.

As the winter of 2002-03 winds down, it appears Mother Nature is a loyal reader. This year will hopefully serve as a reality check on the hype that seems to accompany each announcement of an El Niņo.

Historically, a weak-to-moderate El Niņo in the tropical Pacific means that average conditions in the southern United States are wetter and a little cooler than normal, while the north is warmer and drier. On the West Coast this translates into generally dry weather from Northern California into Oregon and Washington, near-normal conditions in the central part of the state, and wetter-than-normal weather in Southern California.

This winter obviously did not follow form. Rainfall from Northern California northward was near-normal to slightly above -- the reverse of the expected pattern. It was slightly below normal in the center of the state and near-normal to slightly above in the south.

Elsewhere across the country, the Northeast was very cold and snowy -- a big deviation from a typical El Niņo.

So what happened?

The single greatest influence on weather is the seasonal change due to the Earth's tilt. El Niņo is second, followed by a handful of other atmospheric players such as the Pacific Decadal Oscillation, the North Atlantic Oscillation and the Arctic Oscillation. These are periodic events characterized by long-lasting fluctuations in sea surface temperature or atmospheric pressure.

This year it appears that our moderate El Niņo had to compete with a strong North Atlantic Oscillation and a very strong Arctic Oscillation. These tend to produce more than the usual number of polar and Arctic air masses, and are at least partly responsible for the cold, snowy season in the Northeast.

They also set off a series of events in the atmosphere that result in ridges of high pressure over the West Coast, which block storms and lead to drier weather than usual here.

The bottom line is that each time we think we know where a piece fits into the jigsaw puzzle we call climate, another piece turns up that needs to be fit in as well.

Q I am sure you have noticed that filmmakers ignore the differences in the speed of light and the speed of sound when depicting lightning and thunder in their films. I grew up on the eastern prairies of Colorado and learned to automatically count the seconds between the flash of lighting and the rumble of thunder to calculate the distance to the lightning strike. In movies the flash and sound are mostly simultaneous. Ralph Wheeler - Palo Alto

A Unfortunately, a lot of poetic license is taken with meteorology on television and in the movies. Unless a lightning strike is very near, there will be a noticeable delay between the time you see the lightning and hear the thunder. This is because light travels at 186,000 miles per second and sound at only 1,100 feet per second. At this rate, it takes sound about one second to travel one-fifth of a mile, while light is seen almost instantaneously. This is why each five seconds between a flash of lightning and a clap of thunder means the lightning strike was one mile farther away.

Q What causes the steam to rise from rooftops on a frosty morning? Jeanne Lovell - Santa Rosa

A As the warming rays of the sun strike a frosty roof, it can cause the frozen water to turn directly into water vapor without melting first, in a process called sublimation. If the surrounding air is cold enough, the water vapor will immediately condense into tiny droplets that look like steam.

Q I have heard the expression ``it's raining cats and dogs'' quite often, but it has never been taken seriously. More recently I heard that it rained frogs -- and this was not a joke. I don't believe it meant that frogs actually came from clouds, but that they somehow got picked up into the sky and dropped back down. What is the explanation for this? Holly McReynolds - Petaluma

A If it's raining cats and dogs, you should be careful that you don't step in a poodle!! But seriously, there are documented accounts of everything from frogs to fishes and even maggots being swept aloft by tornadoes or waterspouts and then falling out with rain at some distant location.

Jan Null, founder of Golden Gate Weather Services, is a retired lead forecaster with the National Weather Service. Send questions to him c/o Weather Corner, 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 or fill out a form online at