Upper Air Pattern Changes: Wetter Argentina

Charts of the day: Current and projected rainfall pattern.

Discussion: During the past 7 days, Central Brazil trends wetter as thunderstorms have percolated. Thunderstorm activity in Argentina has shifted to the primary growing areas in the East while Northern Argentina has gone dry. Marine heat waves (located either side of South America) inspire subtropical high pressure ridging to overachieve. One example is the short-range forecast not only drying Argentina but causing excessive heat. To compensate for the high pressure and attendant dryness and anomalous heat, nearby regions gain low pressure and heavy rain occurring over northwest continent into early next week. In the 6-10-day forecast the subtropical ridge splits and allows low pressure to form over Bolivia forcing the wet weather southward into Argentina.

Week-2 Valid February 16-22, 2025: Wetter Northern Argentina.

Discussion: Staying consistent, ECM 11-15-day forecast is used for the week-2 outlook. Indicated is patchy excessive heat, not hysterical heat as other models indicate. The upper air pattern is configured to support additional heavy rain in Northern Argentina. Note the feast or famine rainfall pattern: Heavy rain or very dry!

Week-3 Valid February 23-March 1, 2025: Thunderstorms in Argentina; Northeast Brazil is wet.

Discussion: Upper ridge over the MHW east of South America dominates. The upper ridge over the MHW west of South America is fading. The upper ridge position favors anomalous heat over Argentina and Southeast Brazil. Wet weather associated with a weak upper low on the central West Coast could force thunderstorm activity into Argentina. East/Southeast Brazil is dry.

Week-4 Valid March 2-8, 2025: Wetter trend Argentina.

Discussion: The upper ridge shifts southward to the east of Argentina while an upper low forms off the Chile Coast. The sensible weather pattern is wetter in Argentina, staying dry in East Brazil, and favoring just Southeast Brazil for anomalous heat.