La Nina May Be Bearer of Gloom

Government forecasters are detecting the possible return of La Nina, the weather pattern associated with the gloomy June fog in Southern California and persistent droughts throughout the area.

La Nina, which means “The Little Girl” in Spanish, is an abnormal cooling of water temperatures in the equatorial Pacific.

Vernon Kousky, a research meteorologist with the National Oceanic and Atmospheric Administration, said that over the last few months the Pacific has cooled by 2 to 5 degrees just off the western coast of South America, suggesting the emergence of a weak La Nina.

This possible La Nina follows last year’s weak El Nino, the ocean condition typified by warmer than normal temperatures in the equatorial Pacific.

Bill Patzert, a satellite oceanographer at the Jet Propulsion Laboratory in Pasadena, said this La Nina is expected to be mild, although it is already proving temperamental.

The current ocean cooling is bringing drier, cooler, foggier weather to coastal California, suggesting that the gray June gloom that Los Angeles has been experiencing probably won’t lift anytime soon.

In the spring, cooler ocean temperatures contrast with warmer urban coastal areas, resulting in gray fog being drawn inland. Patzert said if La Nina conditions persist, the tendency for “gloom” may last into August.

Evidence of cooler ocean temperatures comes from special buoys scattered throughout the equatorial Pacific. Satellites also precisely measure the height of the ocean’s surface. Differences in the sea height indicate changes in temperature because colder water takes up less space. Lower sea surface heights are an indication of cooler ocean surface temperatures.

The cooling of the Pacific causes the jet stream, responsible for weather patterns across North America, to enter the United States from the Northwest, dive down into the Midwest and then head back up the East Coast. This pattern causes storms throughout the Midwest and East, but bypasses the Southwest, resulting in drought conditions in California.

Kousky said the current weather system will cause more thunderstorms in Ohio and Tennessee and, if conditions persist, possibly increased hurricane activity for the East Coast. Wetter than normal conditions may also develop over northern Australia, Indonesia and southeastern Africa later this year.

Lately, the Southwest has been stuck in a dry spell, the result of the 1998 La Nina, which persisted until last year when a moderate El Nino temporarily returned conditions to normal.

This drought and the recent attack of June gloom may be part of a bigger weather transition, Patzert said. A 50-year cycle know as the Pacific Decadal Oscillation seems to be entering a cooler phase last seen a half-century ago.

In the 1980s and 1990s, Los Angeles International Airport reported an average of 20 fog days each year. In the 1950s and 1960s, 40 fog days a year was the norm.