448
FXUS20 KWBC 052051
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
351 PM EST Thu Mar 05 2026

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

Forecast Bulletin 05 March 2026 at 2045 UTC:

The latest model guidance continues to insist that over the next
three days, the areas with the most consistent rainfall will be
over a significant portion of Brazil, Peru, northwestern Bolivia,
western Ecuador and western Colombia. For Brazil, the areas with
the highest rain could be in isolated sections of Acre and
Amazonas, the eastern sectors of Mato Grosso, most of Para into
Amapa, and many sectors of eastern Tocantins and Maranhao with
bordering states. The GFS model continues to be very aggressive
with an area of over 125mm across northern Para into Amapa over
the next 24 hours, but the ECMWF model continues to be shy. It
pays to know that recent observations confirm that the GFS model
has been handling that particular situation better, therefore we
will side with the GFS model and forecast the higher amounts of
rain over the area. That said, the expected rainfall in that area
will be highest today into Friday, then lower amounts are forecast
on Saturday and Sunday. The expected rainfall over north central
Argentina will be due to thunderstorms activity near low-level
troughs and moisture convergence, with 3-day accumulations that
would be mainly up to 100mm but isolated higher is possible.

For today and tonight, convection over Brazil is expected across
many sectors, but northern Para into Amapa - mentioned earlier -
would have significant rainfall, as well as southern Para and
portions across eastern Tocantins and nearby states. The shower
and thunderstorm activity expected across the Amazon Basin will
once again be largely driven by abundant moisture, diurnal
heating, and low-level convergence.

Friday into Saturday, there will be a cold front across Argentina
into Uruguay. But the most active sections will be north of 30S ,
where significant shower and thunderstorm activity is forecast.
Several low level troughs will cause convergence across tropical
South America, and the Bolivian high causes a relative upper level
jet in its southern periphery, over northern Argentina into
southeastern Brazil and Uruguay. The rainfall totals would be up
to 70mm over northwestern Argentina, while lower amounts of rain
are expected elsewhere, but the rainfall coverage overall will be
widespread. That being said, a significant portions of Para in
Brazil could observe as much as 125mm in scattered thunderstorms
with significant low-level moisture convergence near troughs. The
scattered thunderstorm activity is expected to continue through
the weekend into Sunday. There will be enough moisture to help
fuel efficient rainfall production over tropical South America,
particularly across the aforementioned areas of Brazil.

In the mid to upper levels, in the rest of today into tonight, a
weak trough will be moving into northern Chile and Argentina. Some
divergence and diffluence is expected over northern Argentina
tonight and Friday, which will contribute to the development of
thunderstorms in that region. A pronounced ridge will be moving in
late Friday into Saturday into the southern half of the continent,
which will keep things fairly stable and dry, but another trough
will move in late in the weekend, contributing to rainfall
development late Saturday into Sunday.


Alamo...(WPC)


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