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Charts of the day: 90-day rainfall pattern and upper air.


Discussion: Since late July, extreme precipitation patterns have set-up across southwest/southeast Brazil (wet) and northeast Argentina to far southeast Brazil (dry). The wet weather is caused by a persistent upper-level low-pressure trough across Southeast Brazil. Operational models (through 15 days) maintain the upper trough position.

Week-2 Valid October 31-November 6, 2022 (previous below): Cool forecast trends cooler; rains shift into Northeast Brazil.

Discussion: Operational models are too dry, given persistence, across east/southeast Brazil. Consequently, cluster 2 of ECMWF “weeklies” is selected for next week’s forecast which offers the widest aerial coverage of Northeast Brazil wet weather. Argentina is certainly very dry. The upper trough pattern delivers unusually cool weather for early November.

Week-3 Valid November 7-13, 2022: Brazil flips drier; Argentina is hot.

Discussion: The upper trough is offshore Southeast Brazil. The rainfall pattern shifts drier although showers return to Paraguay and (also) generate across Western Argentina. Anomalous heat develops across Argentina thanks to stronger than normal subtropical ridging.

Week-4 Valid November 14-20, 2022: Northeast Brazil turns wet again; Northeast Argentina is dry.

Discussion: The upper trough backs westward slightly propelling wet weather across Northeast Brazil. On the back side of that convective rain, subsidence dries-out Southeast Brazil/Northeast Argentina.