South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
223 PM EST Mon Nov 10 2025

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

South American Forecast Bulletin for 10 November 2025 at 1920 UTC

In the southern portion of the continent, the Subtropical Jet
Stream is located over northern Chile, into northern Argentina, as
an upper level closed low is located to the west of Chile over the
Pacific Ocean and weak ridge axis extends along the eastern coast
of Argentina on Monday morning. By the evening hours, the closed
low is finally crossing over the Chile, weakening and becoming a
shortwave trough as it interacts with the Subtropical Jet over
northern Chile and Argentina. As these systems interact,
diffluence increases over the northern Patagonia region and
Central Argentina. In the lower levels of the atmosphere, low
level jets over northern Argentina are transporting moisture into
the central regions of the country, as frontogenesis develops from
the Cuyo Region into Buenos Aires province by Monday night. As a
result, the aforementioned regions can expect moisture convergence
along the frontal boundary and an increased risk of severe weather
with the assistance of the upper level dynamics. In central Chile,
a weakened cold front and occlusion are entering the country and
favoring light precipitation from Araucania to north Aysen. On
Tuesday, the presence of the upper level shortwave trough is
expected to propagate eastward into central Argentina, while still
feeling the presence of the upper level jet stream over
north-central Argentina and Uruguay. This will assist in
propelling the low level cold front to continue north and east
from northwest Argentina into southern Uruguay, and the
development of a prefrontal trough from the Chaco Region extending
into the Lagoa dos Patos region in Brasil. In addition, the low
level jets continue to transport moist air into the region. These
conditions will favor maxima of 20-35mm from south Paraguay into
Northwest Argentina and from Buenos Aires to the Sierra de Cordoba
region, and this includes the risk of severe weather on Tuesday.
In the Austral and Sur regions of Chile, new progressive frontal
boundaries continue to propagate in the region, favoring moisture
convergence along the mountainous region. In the upper level, the
entrance region of the Polar Jet is expected over Austral Chile by
Tuesday evening, which will assist in enhanced precipitation in
the region, with maxima of 20-35mm in Austral Chile. On Wednesday,
in the upper levels, the shortwave trough enters the southern
Atlantic Ocean, while interacting with the upper level ridge to
the north, and thus the jet stream is strengthened from north
Chile through Argentina, into Paraguay, south Brasil and into
Uruguay. The area of increased diffluence is expected over
portions of Paraguay and south Brasil, which will favor
significant troughing in the lower levels over these regions. The
frontal boundary over Argentina is expected to be located from the
border region between Argentina and Paraguay, into the Mesopotamia
region, and into Rio Grande do Sul, by Wednesday evening. While
low level jets were transporting moisture into the region over the
past few days, significant moisture convergence is expected from
the Chaco region into central Paraguay and portions of southern
portions of the Pantanal and Parana River Basin regions of Brasil.
The upper level enhancement from the diffluence associated with
the jet stream and upper level trough will favor severe weather in
the region as well. North Paraguay can expect maxima of 50-100mm
with a slight risk of severe weather. From Chuquisaca-Bolivia to
Salta and Formosa-Argentina expect maxima of 30-60mm with a slight
risk of severe weather. From southern Santa Cruz-Bolivia to Mato
Grosso do Sul-Brasil expect maxima of 40-80mm with a slight risk
of severe weather. From the southern portion of Chaco Region to
south Paraguay expect maxima of 20-45mm with a slight risk of
severe weather. To the south, the presence of the upper level jet
continues over the Austral region of Chile, while a new frontal
boundary enters the region. Expect maxima of 20-35mm with a chance
of snow in higher elevations.

In the tropical regions of South America, the upper level systems
include the continued presence of the Subtropical Ridge over
Brasil. This ridge is located between two upper level troughs, one
to the west over the Pacific Ocean, entering Ecuador and Peru, and
the other trough is located east of Brasilian Nordeste region over
the Atlantic Ocean. The presence of a stationary frontal boundary
over central coastal Bahia will bring heavy precipitation over the
next three days. The amount of available moisture along the
frontal boundary and the continued moist onshore flow in the Todos
os Santos Bay region will favor maxima of 25-50mm on Monday. On
Tuesday, the southeasterly wind speed is expected to increase with
the presence of a low level jet, enhancing the effects of the
moist onshore flow along the coastal region, where expect
localized maxima of 40-80mm. On Wednesday, the wind speed
decreases, however, the moist conditions will persist and favor
maxima of 25-50mm. Over the rest of the tropical region of the
continent, the presence of a moist atmosphere and low level
troughs will interact with the diurnal cycle over the forecast
cycle. As these troughs propagate westward along the easterly
trade winds, deep convection is expected to range from scattered
to widespread from the Amazon River Basin into central Brasil.
These conditions will be enhanced with the presence of an
atmospheric Kelvin Wave that is expected over the region during
this week, favoring deep convection over regions of favorable
conditions.

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

Castellanos...(WPC)