South America Autumn 2021 Outlook
By
Jason Nicholls, AccuWeather senior meteorologist
Updated Mar 9, 2021 7:47 PM EDT
Meteorological autumn began across the Southern Hemisphere on 1 March. With that in mind we are going to take a look at what the weather may have in store across South America from March through May.
Heading into autumn we have been looking at a few teleconnections with the continuing, though weakening, La Nina being one of the main teleconnections, at least early on. The current La Nina peaked in December and has been gradually weakening through January and February. Many global climate models show the La Nina continuing to weaken over the next couple of months with neutral ENSO conditions expected to return in April or May. Much of the weakening La Nina looks to be due to a warming of sea-surface temperatures in the eastern equatorial Pacific or the waters closer to South America, while a cool pool of water should persist in the central equatorial Pacific through much of the autumn and perhaps into winter.
The depth of the cool water in the central equatorial Pacific would support this idea of a lingering cool pool of water near the international date line which could result in a transition to a weak central Pacific La Nina or La Nina Modoki in mid- to late autumn.
The following graphic shows composites for precipitation and temperature anomalies across the globe from March through May during La Nina Modoki years and traditional or eastern Pacific La Nina years. The differences are subtle in some areas, but there is a noteworthy increase in the chance for above-normal precipitation across northern South America and much of Brazil with a central Pacific La Nina or La Nina Modoki. La Nina Modoki conditions also tend to favor below-normal temperatures in most areas.
Another teleconnection we looked at is the Atlantic Multi-decadal Oscillation (AMO) which is currently in the warm phase. There is some teleconnection between the AMO and the weather across South America, though not a strong correlation. Below are composites of temperature and precipitation anomalies during autumn with a warm AMO and a neutral ENSO or weak La Nina.
Looking at several teleconnections as well as the overall recent pattern, we came up with several analog years. Here are what our analog years show for temperature and precipitation anomalies across South America during March, April and May.
The various composites show some similarities favoring below-normal temperatures along the coast of Peru and above-normal temperatures in portions of northern and central Argentina. There are also some similarities with many composites favoring above-normal precipitation in parts of northwest South America. Despite these similarities there are also several notable differences between the composites and analogs, so we will take a look at a couple of global climate models.
Looking at the multi-model ensembles (above), there seems to be good agreement in several areas of South America. However, the models disagree with some of our analogs and teleconnections so in short, the autumn forecast is a little trickier. A big part of the differences and challenges is due to a lack of a strong teleconnection now that La Nina is weakening. That means several factors will play a part in the weather this autumn.
After hours of research and looking at most teleconnections, we have come up with our South America autumn 2021 outlook. First, taking a look at temperature anomalies, we expect near- to below-normal temperatures from northwest Brazil to French Guiana and Peru. Part of the reasoning for the lower-than-usual temperatures along the coast of Peru is due to the cool water temperatures along the Pacific coast from central and northern Chile to Peru.
These cool waters may also tend to limit heat in much of Chile this autumn compared to recent years, but we still expect a few short-lived spells of heat in central Chile, including Santiago, especially during March and April. On the other side of the continent, we do expect above-normal temperatures across much of Argentina and perhaps into southern Uruguay. Much of southern Brazil should have seasonal temperatures, but we are concerned for some spells of warmth and perhaps a slight bias toward above-normal for the season. Above-normal temperatures are also expected in northeast Brazil.
Now looking at precipitation, we are concerned for below-normal precipitation in northeast Brazil where usual warmth may tend to worsening drought problems. Meanwhile, above-normal rainfall from northwest Brazil and French Guiana into southern Venezuela and Colombia will continue to raise water levels which will be beneficial for hydroelectric production in portions of Venezuela. The only area of Venezuela that my be drier than normal is the northwest corner of the nation.
The Amazon basin, much of Peru, Ecuador and central and southern Brazil are expected to have close to normal precipitation. However, frequent stalling fronts can lead to a corridor of above-normal rainfall from Santa Catarina into Parana, Sao Paulo and perhaps part of Mato Grosso Do Sul in Brazil into northeast Paraguay. We are also concerned for drier-than-normal conditions in portions of Rio Grande Do Sul, Brazil, northern Uruguay and northeast Argentina. Drier-than-normal conditions are also expected over central Argentina into south-central Chile, while the remainder of Argentina and Chile should have at least near-normal precipitation. Overall, conditions look pretty favorable for summer crop harvesting and winter grain planting and establishment across many of the key crop areas from Argentina to Brazil.
Central Chile, including Santiago, is not expected to be very active with storms this autumn and may end up averaging below-normal for precipitation. However, we do see the opportunity for a couple of precipitation events mainly late in the season. The best chance for above-normal precipitation in Chile looks to be across the far south where storm frequency is expected to increase.
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Weather Blogs / Global weather
South America Autumn 2021 Outlook
By Jason Nicholls, AccuWeather senior meteorologist
Updated Mar 9, 2021 7:47 PM EDT
Meteorological autumn began across the Southern Hemisphere on 1 March. With that in mind we are going to take a look at what the weather may have in store across South America from March through May.
Heading into autumn we have been looking at a few teleconnections with the continuing, though weakening, La Nina being one of the main teleconnections, at least early on. The current La Nina peaked in December and has been gradually weakening through January and February. Many global climate models show the La Nina continuing to weaken over the next couple of months with neutral ENSO conditions expected to return in April or May. Much of the weakening La Nina looks to be due to a warming of sea-surface temperatures in the eastern equatorial Pacific or the waters closer to South America, while a cool pool of water should persist in the central equatorial Pacific through much of the autumn and perhaps into winter.
The depth of the cool water in the central equatorial Pacific would support this idea of a lingering cool pool of water near the international date line which could result in a transition to a weak central Pacific La Nina or La Nina Modoki in mid- to late autumn.
The following graphic shows composites for precipitation and temperature anomalies across the globe from March through May during La Nina Modoki years and traditional or eastern Pacific La Nina years. The differences are subtle in some areas, but there is a noteworthy increase in the chance for above-normal precipitation across northern South America and much of Brazil with a central Pacific La Nina or La Nina Modoki. La Nina Modoki conditions also tend to favor below-normal temperatures in most areas.
Another teleconnection we looked at is the Atlantic Multi-decadal Oscillation (AMO) which is currently in the warm phase. There is some teleconnection between the AMO and the weather across South America, though not a strong correlation. Below are composites of temperature and precipitation anomalies during autumn with a warm AMO and a neutral ENSO or weak La Nina.
Looking at several teleconnections as well as the overall recent pattern, we came up with several analog years. Here are what our analog years show for temperature and precipitation anomalies across South America during March, April and May.
The various composites show some similarities favoring below-normal temperatures along the coast of Peru and above-normal temperatures in portions of northern and central Argentina. There are also some similarities with many composites favoring above-normal precipitation in parts of northwest South America. Despite these similarities there are also several notable differences between the composites and analogs, so we will take a look at a couple of global climate models.
Looking at the multi-model ensembles (above), there seems to be good agreement in several areas of South America. However, the models disagree with some of our analogs and teleconnections so in short, the autumn forecast is a little trickier. A big part of the differences and challenges is due to a lack of a strong teleconnection now that La Nina is weakening. That means several factors will play a part in the weather this autumn.
After hours of research and looking at most teleconnections, we have come up with our South America autumn 2021 outlook. First, taking a look at temperature anomalies, we expect near- to below-normal temperatures from northwest Brazil to French Guiana and Peru. Part of the reasoning for the lower-than-usual temperatures along the coast of Peru is due to the cool water temperatures along the Pacific coast from central and northern Chile to Peru.
These cool waters may also tend to limit heat in much of Chile this autumn compared to recent years, but we still expect a few short-lived spells of heat in central Chile, including Santiago, especially during March and April. On the other side of the continent, we do expect above-normal temperatures across much of Argentina and perhaps into southern Uruguay. Much of southern Brazil should have seasonal temperatures, but we are concerned for some spells of warmth and perhaps a slight bias toward above-normal for the season. Above-normal temperatures are also expected in northeast Brazil.
Now looking at precipitation, we are concerned for below-normal precipitation in northeast Brazil where usual warmth may tend to worsening drought problems. Meanwhile, above-normal rainfall from northwest Brazil and French Guiana into southern Venezuela and Colombia will continue to raise water levels which will be beneficial for hydroelectric production in portions of Venezuela. The only area of Venezuela that my be drier than normal is the northwest corner of the nation.
The Amazon basin, much of Peru, Ecuador and central and southern Brazil are expected to have close to normal precipitation. However, frequent stalling fronts can lead to a corridor of above-normal rainfall from Santa Catarina into Parana, Sao Paulo and perhaps part of Mato Grosso Do Sul in Brazil into northeast Paraguay. We are also concerned for drier-than-normal conditions in portions of Rio Grande Do Sul, Brazil, northern Uruguay and northeast Argentina. Drier-than-normal conditions are also expected over central Argentina into south-central Chile, while the remainder of Argentina and Chile should have at least near-normal precipitation. Overall, conditions look pretty favorable for summer crop harvesting and winter grain planting and establishment across many of the key crop areas from Argentina to Brazil.
Central Chile, including Santiago, is not expected to be very active with storms this autumn and may end up averaging below-normal for precipitation. However, we do see the opportunity for a couple of precipitation events mainly late in the season. The best chance for above-normal precipitation in Chile looks to be across the far south where storm frequency is expected to increase.
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