This is not the first time recently that cold conditions have gripped parts of southern South America as winter approaches in the Southern Hemisphere. Over the past two days, an area of low pressure has positioned itself just southeast of the continent and allowed cold air to filter northward into southern Chile and Argentina. This process will continue over the next few days with temperatures 5 to 10 degrees lower than normal in Argentina from Thursday.
In fact, the western portion of South America, including farther north to Peru, has recently experienced nearly perpetual cool conditions related to an ongoing La Niña event in the Pacific Ocean. During these events, which typically occur every few years, sea surface temperatures (SSTs) in the southeast Pacific cool significantly as colder waters from the deep well to the surface. Current observations suggest that SSTs just off the coast of Peru are between 1.5 and 3.5°C cooler than normal and have been cooler than normal since last fall. The presence of colder water often has a moderating impact on temperatures in South America, but can also have broader impacts on global weather patterns.
One such link suggested by research is with drier than normal weather in the southern United States during the winter half of the year. Since January, conditions have been drier than normal in the desert southwest. For countries like Arizona, critical fire hazards are in place for Tuesday and the return of windier, warmer weather for the weekend suggests they could continue to be a near-term feature.
Meanwhile, an unusually warm air mass that has affected the Iberian Peninsula – bringing maximum temperatures above 40C to parts of southern Spain on Friday and Saturday – is moving east across the south from Europe. New heat is expected to continue from Tuesday and over the next few days in Italy, Greece and the Balkans. Although temperatures will not be as high as in Spain, the aforementioned areas will still be subject to at least the low to mid 30s Celsius for some days, in some parts 10 degrees above the seasonal norm.