South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
301 PM EST Tue Mar 03 2026

GFS data at ftpprd.ncep.noaa.gov/data/nccf/com/gfs/prod/

Forecast Bulletin 03 March 2026 at 2000 UTC:

Over the next three days, the most consistent and reliable
rainfall is expected across portions of central to southern
Brazil, Peru east of the Andes into northwestern Bolivia, as well
as parts of north-central Argentina and western Paraguay.
Additional significant rainfall is anticipated across western
Ecuador and western Colombia. Farther south, periods of rain and
mountain snow are expected across the southern half of Chile.

For today and tonight, the heaviest rainfall is expected across
western Ecuador, where totals of up to 45 millimeters are
forecast, with isolated higher amounts possible. Across central to
eastern Brazil, daily maxima of up to 45 millimeters are
anticipated, while central to southeastern Peru and northwestern
Bolivia can also expect totals near 45 millimeters. A small sector
of north-central Argentina may receive up to 70 millimeters of
rain, accompanied by a slight risk of severe thunderstorms. Across
southern Chile, precipitation will include both rain and mountain
snow.

On Wednesday into Thursday, convection strengthens across eastern
to northeastern Brazil, where rainfall totals may reach up to 80
millimeters. Across northern Argentina, particularly along a
low-level trough, rainfall amounts of 60 to 70 millimeters are
possible, with a marginal risk of severe weather in the vicinity
of enhanced upper-level support. Shower activity also persists
across portions of western and southern Brazil during this period.

By Thursday into Friday, sections in and around Para of Brazil
continue to experience active convection, with daily maxima of up
to 50 to 70 millimeters expected. Northern Argentina may again
receive 60 to 70 millimeters of rain in association with another
low-level trough and favorable upper-level divergence. Daily
showers and thunderstorms remain widespread across the Amazon
Basin, largely driven by abundant moisture, diurnal heating, and
low-level convergence.

In terms of moisture availability, near-normal to slightly
above-normal precipitable water values are expected across much of
Brazil, and along eastern Peru over the next several days. Similar
moisture conditions extend across northern Argentina, northern
Bolivia, western Paraguay, and Uruguay. In contrast, northwestern
Brazil into southern Venezuela will experience a pocket of notably
drier air. Southern Argentina and Chile will generally remain near
to slightly below normal in moisture, with the exception of a
narrow band of enhanced moisture moving northward across southern
Chile, contributing to rain and mountain snow.

At upper levels, a strong jet moves into the southern portion of
the continent, with winds approaching 100 to 150 knots across
southern Chile and southern Argentina. An upper trough extending
into northern Argentina over the next couple of days may enhance
divergence aloft and contribute to the risk of strong to severe
storms in that region. Farther south, another pronounced trough
remains anchored near the austral tip of the continent. Across
tropical South America, winds remain comparatively light beneath a
broad upper-level ridge centered over Brazil, resulting in limited
large-scale dynamical forcing north of approximately 20 degrees
south.

At mid levels, the overall pattern mirrors the upper-level
configuration, with stronger troughing confined to the southern
cone while a broad ridge dominates much of Brazil. This ridge
limits large-scale instability across tropical South America,
although weak troughs are present across western to southern
Brazil and parts of southeastern Brazil. By Thursday into Friday,
a mid-level trough begins to influence northeastern Brazil,
potentially enhancing convective development in that region.

At low levels, several troughs are present over the continent.
Today, a trough is located across southeastern Brazil, while
another extends across northern Argentina west of Uruguay. On
Wednesday into Thursday, a low-level trough extends from southern
Peru and western Paraguay into northwestern Argentina, with
additional troughing across southern and central Brazil. By
Thursday into Friday, troughing redevelops across northern
Argentina into Uruguay, while additional low-level troughs are
present across eastern Brazil and across portions of Bolivia into
western Brazil. These features, in combination with adequate
moisture and upper-level support, contribute to the potential for
stronger convection across northern Argentina and adjacent areas
during each day of the period.

At the surface, a cold front across southern Argentina and central
to southern Chile continues to move east and north. By Wednesday,
a stationary front is expected to become established near and just
north of Buenos Aires and around Uruguay, where it may enhance
low-level convergence and moisture pooling. This boundary remains
stationary through Thursday into Friday.


Alamo...(WPC)