Published Tuesday, February 12, 2002 in the San Jose Mercury News


Special to the Mercury News

Exploding Six California Myths About El Niņo

The National Oceanic and Atmospheric Administration (NOAA) recently issued a press release about the possible return of El Niņo this summer. And even before the ink was dry on the release, yet another round of El Niņo hype was beginning, with the expectation that California was about to be washed into the Pacific.

But what really is El Niņo, and what does it really mean for Californians? Let's try to put some of these myths about this weather phenomenon into perspective.

Myth 1: El Niņo will come to California this year. No -- El Niņo never comes to California. It is a phenomenon that periodically occurs in the warm equatorial waters of the Pacific Ocean. Normally the trade winds along the equator push the warmest waters into the western portions of the Pacific. But about every three to five years the trades slacken, or sometimes even reverse direction, and warmer-than-normal water accumulates along the equator in the central and eastern Pacific. This warming is called El Niņo, referring to the ``Christ child'' because its effects are greatest in the winter and often disrupt fishing along the South American coast around Christmas. (The converse case, La Niņa, is when the waters of the eastern Pacific are cooler than normal.)

Myth 2: All El Niņos are the same. While El Niņo only occurs in the tropics, its impact is felt in many parts of the world. This happens because the location of the huge mass of warm water causes the location of the jet stream, or storm track, to shift. As a consequence some regions are warmer or colder, or wetter or drier, than normal. However, not all El Niņos have the same strength of location, and consequently their impacts can vary significantly. In general, the larger the area and the greater the warming of the eastern Pacific's equatorial waters, the greater the impact on other regions. Since 1950 there have been nine years with weak-to-moderate El Niņos (1951, 1957, 1963, 1969, 1976, 1977, 1991, 1992 and 1993) and six years with strong El Niņos (1965, 1972, 1982, 1987, 1994, and 1997).

Myth 3: There are El Niņo-spawned storms. No, El Niņo does not actually create any storms. It simply shifts the usual pattern so that some areas are more susceptible to certain conditions. Consequently, El Niņo should not be used as an adjective in phrases such as ``El Niņo flooding.''

Myth 4: We will see the impacts from El Niņo any day now. The long-range climate forecasts from NOAA actually called for an El Niņo already to be occurring, but the forecast onset has been pushed back several times. And it is just that -- only a forecast. Even if there is a warm-up in the tropical Pacific this summer, the earliest effects on California would not be felt until next winter.

Myth 5: When there is an El Niņo, there is lots of rain in California. The answer is not always and not everywhere. Historical records for the past five decades in central California show that during strong El Niņo events the rainfall has been above normal four of the six seasons, but it has been below normal for five of the nine weak El Niņos. Over the same span, Northern California had three wet years and three dry years during strong events, with five above-normal seasons during the nine weak-to-moderate El Niņos. Southern California showed more of a wet bias during strong El Niņos with above-normal rain in five of the six seasons and above-normal rain during five of the nine weak-to-moderate events. The bottom line is that California can get wet during El Niņo, but not always. As a matter of fact, the California drought in 1976 was during a weak El Niņo. It is important to keep in mind that El Niņo is not the only thing happening in the atmosphere and that other patterns can either enhance or detract from its overall impact.

Myth 6: El Niņo means disastrous flooding for California. Occasionally, but it is just as likely that California will have significant flooding in a non-El Niņo year. Of the 10 costliest flood years in California since 1950, only four happened during a time when there was an El Niņo. Two others occurred during seasons with La Niņa, and the final four were when the temperature of the tropical Pacific was near normal.

The major weather pattern that causes flooding in California is when a strong surge of subtropical moisture dumps copious amounts of rain over a portion of California for five to seven days. This is the so-called pineapple connection, and it is actually slightly more prevalent during years when there is no El Niņo. The last strong El Niņo in the winter of 1997-1998 is a good case study of a wet El Niņo year, but one with no major flooding. Despite nearly double normal rainfall over most of California, there was nearly twice the number of days of rain with no huge concentrated deluges, and statewide damage totals were about $500 million. Compare this with the flooding that took place around New Year of 1997, a period with no El Niņo, when a week's worth of warm pineapple-connection rain resulted in $1.8 billion in damage statewide.

So, what does it all mean? From the current forecast there is a possibility of an El Niņo this summer that might have some impact next winter, depending on whether it is a weak or strong event and what else might be occurring at the same time. Stay tuned.

To learn more about El Niņo visit

Q.  Often on these cold mornings, I see frost on the roofs of houses in the neighborhood and ice on car windshields. But according to the weather reports, the low for our area was around 35, and my max-min thermometer also indicates that the temperature did not go below 32. Is it possible for ice to form when the air temperature is above 32, or is my thermometer inaccurate? Don Gentner - Palo Alto

A.  A great question, and one I've been asked frequently of late. There are a couple of reasons why there can indeed be frost even when the air temperature is greater than 32. One is that most air temperatures are taken at about five inches above the ground, and the temperature at ground level is usually 3 to 4 degrees cooler. Additionally, solid objects generally cool off faster than the air, and thus these objects can be below freezing while the air temperature is above 32, and therefore moisture in the air can condense on them as frost.
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 or e-mail them to . Please indicate in your e-mail what city you live in.

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) 657-2246Š, FAX them to (510) 315-3015Š or e-mail them to  Please indicate in your e-mail what city you live in.