This happening is called El Nino and is used by weather forecasters to make long-range weather predictions. They also know that El Nino will unusually bring heavy rains to the southwestern part of the United States and make the central part of the country drier at the same time. According to research, weather forecasters used to know about the coming weather with certainty. Now everything has become completely different. El Nino itself used to be (4)_____ .