Farmers in Montana can look to Peru for an early spring weather forecast, a new study suggests.
The study links extreme Montana weather to fall Pacific Ocean temperatures near Peru, according to a Montana State University researcher who analyzed 100 years of weather data.
If the average surface temperature of the ocean near Peru is warmer than normal from November through March, fishing off the coast of Peru will be poor and Montana will experience El Niño conditions from the following December through June, said Joseph Caprio, professor emeritus at Montana State University. An El Niño climate regime generally means Montana will be warm and dry.
If the average sea surface temperature is cooler than usual from November through March, fishing off the coast of Peru will be good and Montana will have a cool, wet spring, like the one experienced this year during La Niña, Caprio said. He added that weather in different areas of the United States responds differently to El Niño or La Niña.
Caprio said Peruvian fishermen knew hundreds of years ago that ocean temperatures affected their livelihood. And scientists have long known that certain weather conditions around the globe are linked to El Niño. Meteorologists with the National Ocean and Atmospheric Administration (NOAA) make long-range forecasts by monitoring sea surface temperatures, atmospheric pressure, wind, air temperatures and cloudiness in various areas of the Pacific Ocean.
Caprio focused on the sea surface temperatures in the area that's associated with Montana weather. That area is off the Peruvian coast and near the equator. It covers about 550 miles (885 kilometers) from north to south and 4,100 miles (6,600 km) east to west.
Caprio specifically wanted to determine the effect of El Niño on extreme daily temperatures and precipitation in Montana.
"Since El Niño sea surface temperature anomalies tend to persist for many months and have predictable climatic associations, it is prudent to undertake research to understand how El Niño affects extremes of weather for individual locations in order to provide useful information for decision makers," Caprio wrote in a paper he published in the Intermountain Journal of Sciences.
Compared to normal years, El Niño years tend to have about 20 percent more days with extreme high daytime temperatures, 20 percent fewer days with extreme low nighttime temperatures and 20 percent fewer days with high precipitation amounts, Caprio said.
"An increase or decrease of extreme daily weather occurrences can impact natural resources and a wide range of human activities, including agriculture, forestry, recreation, construction and other businesses," Caprio said.
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