South America Pattern Change Ahead

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Fig. 1: GFS 15-day upper air pattern forecast across South America.

South America discussion: A pattern change is indicated for the second half of January. Previously, a semi-permanent upper trough was located southeast of Brazil and enhancing historic rainfall for that nation the past couple months. The GFS 15-day outlook indicates a pattern change (Fig. 1). An upper-level ridge crests just-off the far southeast coast of Brazil. The new climate pattern through the remainder of January will feature a northern shift of the Argentina/Paraguay hot weather, a drier pattern for Brazil and much needed wet periods across Argentina.  

The searing heat lasts into the weekend in Argentina. However, a series of cold front(s) break down the heat with scattered showers and thunderstorms this weekend. A more organized wet weather event is focused on Tuesday when potential for several in. of rain is expected (Fig. 2). The wet weather pattern lasts through both the 6-10-day and 11-15-day periods (Fig. 3-4) due to the moist tropical fetch southward into Argentina on the back side of a subtropical high-pressure area just offshore southeast Brazil.

Fig. 2-4: GFS rainfall forecasts for next Tuesday and the medium-range across Argentina.