The end of last year may have brought to a close a decade of strange weather, but it didn't bring an end to La Nina.

That cold-weather cousin of El Nino will extend her chilly fingers into the coming haying season, predict meteorologists. And that could give some farmers more than the usual climatic challenges.

Meteorologist Evelyn Browning Garriss, who authors a monthly weather publication called The Browning Newsletter, says the decade of the '90s was an unusual one, weatherwise.

"We had an El Nino for four years in a row, then a break, and then another El Nino," she says. "That's very unusual since El Ninos usually occur once every four to seven years."

What causes these south-of-the-border-sounding weather systems? El Nino is a warming of the sea surface temperatures in the Pacific Ocean around the equator due to weakened trade winds. Conversely, La Nina results from strong trade winds and a drop in ocean temperature in the southern Pacific. In both cases, Peru and other South American countries feel the climatic effects first. Scientists there, as well as in Hawaii, have begun to associate the onset of these weather patterns with seismic activity within the earth, specifically around major volcanic areas.

An El Nino, and the often- trailing La Nina, can dramatically affect precipitation patterns, explains Browning Garriss, who studies weather patterns from her home office in New Mexico.

"With La Nina, we typically see droughts occurring in South and Central America, as well as in California and the Southwestern part of this country. Whereas the Pacific Northwest is usually hit with more than enough precipitation."

La Nina's effects on the middle of the country are less clear, since its weather is less dominated by westerly wind currents.

"We're seeing more Arctic and Pacific air affecting our weather patterns now," says Bruce Watson, consulting meteorologist with Bruce and Frank Watson, St. Paul, MN. He says La Nina's effects will most likely fade away in late summer or fall.

Here's a brief summary of regional weather predictions for the coming haying season: * The Upper Midwest can expect to see temperatures close to normal overall, with slightly below-average rainfall, predicts Watson.

"I expect normal precipitation levels for Wisconsin, Minnesota and the Dakotas in May and June. Then it will turn toward the dry side in July and August."

* The Southwest will see dry, abnormally warm conditions throughout much of the spring and summer, says Browning Garriss.

* The Pacific Northwest, conversely, will have more than enough precipitation this season, she notes.

* The Atlantic states will experience a shift from colder-than-normal weather to a warmer trend, which will stir up more tropical storms.

"That's a very typical effect of La Nina. This part of the country will probably have a drier-than-average spring and early summer, and a wetter-than-average late summer and fall."

* The east-central states may see more storm activity in late spring and early summer, as La Nina has been known to increase the incidence of tornadoes from Ohio to the Tennessee River Valley.

"With La Nina still in the picture, many of the same weather conditions farmers dealt with last year will be affecting them again this season," says Browning Garriss.