WEATHER
CORNER
BY
JAN NULL
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
http://ggweather.com/links.html#research.
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
weathercorner@ggweather.com
. 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) 657-2246, FAX
them to (510) 315-3015 or e-mail them to
weathercorner@ggweather.com.
Please indicate in your e-mail what city you live in.