South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
331 PM EDT Fri Oct 24 2025

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

South American Forecast Bulletin for 24 October 2025 at 1930 UTC

The main story today is the potential for severe thunderstorms
from northeastern Argentina to southern Uruguay, associated with a
cold front that is moving north, which will encounter a northerly
low-level jet, causing moisture convergence in the lower levels.
This will also combine with favorable mid to upper level dynamics.
Therefore, Strong thunderstorms, probably producing strong winds,
hail and heavy rainfall may be observed ahead of the cold front
today and into the weekend. This frontal boundary will gradually
move north into Paraguay and Bolivia this weekend.

In the upper levels, there is a broad trough extending from the
southeast Pacific and Austral Chile, all the way up to around 20N.
This trough is tilted west, and will move through central to
southern South America this weekend, while a secondary trough
moves in to Austral South America on Sunday, and another shortwave
trough is expected to enter central Chile. The upper levels also
will have a strong jet that will be particularly pronounced over
northeastern Argentina late tonight into early Saturday, into
Uruguay from Saturday into Sunday. This jet will provide
divergence aloft for the development of thunderstorms over the
area.

The mid levels and the upper levels are relatively well stacked
vertically. The same pattern of troughs are suggested in the mid
levels by the model guidance. That said, the mid level jet over
Argentina is forecast to be over Northern Patagonia tonight into
Saturday. Another mid level jet is forecast to be over
northeastern Argentina and Uruguay for Saturday into Sunday. The
latest guidance also suggests that a very strong mid level jet
will be moving in across Austral South America this weekend.

In the lower levels, a series of frontal boundaries moving into
the southern half of South America. In addition, low level jets
across central South America from the north will be observed
today, but these will shift to southerly jets by Sunday. The low
level jets could bring deep moisture from the north that will
interact with the frontal boundaries, providing plenty of moisture
for the expected strong thunderstorms.

The situation across Tropical South America is expected to be
generally influenced by the diurnal and local effects. The mid and
upper levels are, for the most part, dominated by a high pressure.
There is drier than normal air across the eastern portions of
Brasil, but western Brasil will have higher than normal moisture,
as well as Colombia and eastern and northern Peru. This general
setup will favor for the most significant rainfall to occur over
central to western Brasil. However, there is some rain forecast
across the eastern coast of Brasil from around Espirito Santo to
the Brazilian Nordeste today and Saturday, while most of the rain
would be limited to the coast of Bahia on Sunday.

For the latest available charts please visit:
https://www.wpc.ncep.noaa.gov/international/sam_day1-3.shtml

Alamo...(WPC)