South America Calling

Frontal Boundaries Bringing Showers to South America

John Baranick
By  John Baranick , DTN Meteorologist
A weak front will produce some lighter showers for Argentina and southern Brazil through the weekend. But another frontal boundary should produce better rainfall chances and amounts by the middle of next week. (DTN graphic)

Winter wheat is starting to get a bit more active across the whole of South America. Wheat has been developing and has reached flowering for some areas of Parana and Rio Grande do Sul in southern Brazil. But with winter waning and the head toward spring, areas in Argentina will start to get more active as well.

Now it becomes much more important to look at the near-term weather to get a gauge of how wheat is doing. And we might as well take a look at the lead up to spring corn and soybean planting as well.

Soil moisture in southern Brazil is currently below normal, but still adequate enough for wheat this time of year based on satellite data through Aug. 15. Argentina falls into much of the same category. Soil moisture is somewhat below normal, but still adequate for this stage in the crop year. Being a little behind normal at this point in the year, it will be important that the spring season does not fall behind further and storm systems that move through bring beneficial rainfall before summer hits. Currently, a frontal boundary is sitting right through central Argentina on Aug. 19. This front is not producing much precipitation and temperatures north of the front are well above normal all the way into Brazil. Highs have been in the 30s Celsius (upper 80s to near 100 degrees Fahrenheit) and will continue until the front pushes northward. South of the front, we are seeing temperatures go back to normal. This front will move into northern Argentina and Rio Grande do Sul, Brazil by the weekend but stall or wash out. Rainfall amounts will generally be light, but could be moderate in a couple of spots where they get hit a couple of days in a row.

But a second, stronger front will be developing during the weekend across southern Argentina's growing areas. The front will take some time to organize but will move northward to northern Argentina and southern Brazil by the middle of next week. As it does, models forecast much more widespread and heavier rainfall, especially over Rio Grande do Sul. The front should get through much of the wheat areas of southern Brazil, but may not reach into the main corn and soybean growing areas.

Temperatures behind this second front will also be much lower. Temperatures will drop an initial 2 to 4 degrees Celsius (4 to 9 degrees Fahrenheit) as this front moves through, but could drop further as the front pushes farther north into Brazil. The latest run of the European model is attempting to drop temperatures 6 to 10 degrees Celsius (10 to 18 degrees Fahrenheit) below normal across Argentina and southern Brazil. Widespread frosts and potential freezes could have impacts for wheat that may be farther along in parts of Argentina. The temperature drops are not as dramatic for the main wheat areas in southern Brazil and frosts are currently not expected, but growth could be slower.

Drought has been going on in central Brazil for almost the last five months, which happened due to a quick shutoff of precipitation in March as the annual dry season came about six to eight weeks early. Rainfall is desperately needed to allow planting to begin. Corn can be planted at any time now as long as producers are willing to risk some dryness before the start of the wet season. But soybeans are not able to be planted legally until about the middle of September. The front next week is not expected to bring rainfall far enough north to catch much of the corn and soybean areas, but there is some time for other fronts to provide some rainfall during the next month.

Unfortunately, it appears that La Nina is likely to develop in the Equatorial Pacific during the next month or two. That typically causes a delay in the start of the wet season. When La Nina developed in 2020, the wet season rains were delayed by three or four weeks. While soybeans did well and had a record harvest in Brazil, another delay that drastic would set up for poor winter corn conditions yet again. This will be a situation to watch closely.

John Baranick can be reached at


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