South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
306 PM EST Wed Feb 04 2026

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

Forecast Bulletin 02 February 2026 at 1945 UTC:

On Monday, deep convection is expected over much of the tropical
portion of South America as moisture is converging over portions
of Brasil, Bolivia, Peru, Ecuador, and south Colombia. In the
upper levels of the atmosphere, the Bolivian High is dominating
the region, favoring convection over a large portion of the
continent. In part, associated with the positive phase of the
Antarctic Oscillation, expect upper level troughs to remain to the
south, limiting any northward propagation of frontal boundaries in
the lower levels. As such, much of the precipitation over the
tropical region will be affected by the diurnal cycle. In
addition, the region is experiencing close to seasonal and above
normal amounts of precipitable water, particularly in portions of
southeast Brasil and along the foothills of the Andes Mountains in
Peru and Bolivia. Of note on Monday, a shortwave upper level
trough is propagating over northern Argentina, bringing unstable
conditions from central Bolivia, Paraguay, and into southern
Brasil. By activating the South American Low Level Jet, enhanced
moisture advection into these regions will favor heavy
precipitation and deep convective conditions on Monday. The
Pantanal region of Brasil can expect maxima of 50-100mm,, while
the Parana Basin can expect maxima of 40-80mm. From the Selva Alta
in Peru through the Yungas in Bolivia expect maxima of 35-70mm.
Similar totals are expected in northern Peru, Rio de
Janeiro/Espirito Santo, and across Mato Grosso and Tocantins due
to significant moisture convergence in the lower levels. On
Tuesday, these condition are expected to continue in south Brasil
and along the foothills of the Andes Mountains, while dry air is
advected into northeast Brasil. With this decrease in moisture to
the north, expect moisture to converge in regions that will
already see heavy precipitation on Monday. The Cerrado region can
expect maxima of 35-70mm, while the Pantanal can expect maxima of
40-80mm. The southern portion of Brasil can expect generalized
maxima of 25-50mm, with a potential for localized higher amounts.
Along the Selva Alta and the Yungas, the advection of moisture
along the SALLJ will continue to interact with the terrain and
favor maxima of 35-70mm on Tuesday. By Wednesday, a retrograding
upper level trough enters the eastern Brasil region, interacting
with the Bolivian High and assisting with the advection of drier
air into the region from the Central Atlantic. With this upper
trough, the presence of the Bolivian High weakens over east
Brasil, favor lower precipitation totals on Wednesday from
Tocantins through the Cerrado region and into the Serra do Mar
region. the heaviest precipitation is expected from the Pantanal
through the Parana Basin as the upper level trough that came from
Argentina has now entered south Brasil, providing unstable
conditions. However, with the decrease of moisture in the region,
expect maxima of 30-60mm. to the north, similar totals are
expected as low level moisture converges over the northwest Amazon
Basin.

To the south, weak upper level troughing remains over the
Patagonia and south Chile. With the presence of the Bolivian High
blocking further northward movement, most frontal boundaries
crossing from south Chile are expected to weaken over the central
portions of Argentina. However, the presence of the SALLJ to the
north will favor moisture advection into central Argentina,
favoring moderate precipitation over the next several days. In
addition, frontal boundaries and troughing will favor lift in the
lower levels, and the upper level troughs increase the instability
in the region. On Monday, expect maxima of 15-20mm in the Sur
region of Chile into the northern Austral region. On Tuesday,
moisture converging along a passing front in the Cuyo/Cordoba
region, expect maxima of 20-35mm, similar amounts are expected in
the southern Patagonia. On Wednesday, expect maxima of 20-45mm in
La Pampa region.

Castellanos...(WPC)