Ag Weather Forum

Favorable South America Rain Outlook

Mike Palmerino
By  Mike Palmerino , DTN Senior Ag Meteorologist
Moderate to heavy rain is featured throughout the South American crop belt from Argentina through central Brazil during the days leading up to Christmas Day. (NOAA graphic by Nick Scalise)

Timely and beneficial rains are indicated for most of South America's crop areas this week, including the dry sectors of Argentina and southern Brazil.

The rain would be useful. Concern has been building in the past few weeks due to very warm-to-hot and dry conditions in Argentina and southern Brazil. These conditions have a possible relationship to a weak La Nina event in the Pacific Ocean. However, the forecast has a change developing, with the heat and dryness giving way to scattered showers and thunderstorms and more moderate temperatures during December 19-25.

In the period ending Dec. 26, almost all major corn and soybeans areas in South America will pick up moderate to heavy rainfall. This is in addition to moderate to heavy rain of up to 3 inches that already occurred in about 60% of the central Argentina crop region during the Dec. 15-17 weekend. This development promises to be less stressful to developing corn and soybeans, and favors the remaining planting in Argentina. This rainfall prospect, if it verifies, should maintain favorable growing conditions through the end of the month.

Close attention will also be given to whether La Nina conditions can re-establish hot and dry weather in Argentina and southern Brazil during January. Our latest calculation of the sea surface temperature departure in the eastern equatorial Pacific for the first half of December was minus 1.0 degree Celsius. This is down from the minus 0.8 degree Celsius departure observed during the month of November.

Meanwhile, the barometric component of the Pacific El Nino-La Nina event known as the Southern Oscillation Index (SOI) has shown some weakness and slippage from La Nina readings. The 30-day average SOI on Dec. 19, was plus 4.37, which is well below the La Nina threshold of plus 8.0. The longer-range 90-day average was barely at the La Nina threshold at plus 8.05. The daily calculation by the Australia Bureau of Meteorology (BOM) of minus 6.18 was actually leaning toward the El Nino category. La Nina continues to be a weak event.

Michael Palmerino can be reached at



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