831
FXUS20 KWBC 141829
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
229 PM EDT Tue Oct 14 2025

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

South American Forecast Bulletin from 14 October 2025 at 1830 UTC

On Tuesday, the southern cone of the continent is seeing the
entrance of a frontal boundary and an atmospheric river with
estimated precipitable water levels of 25-30mm in the Sur region
and the southern Central region of Chile. In the mid to upper
levels, the short wave upper troughing within a wider amplitude
trough is expected to enter the region in the overnight hours of
Tuesday into Wednesday, when the advection of vorticity will
assist with the divergent conditions and favor moderate to heavy
precipitation in the region. The Sur region of Chile can expect
maxima of 25-50mm with the chance of mountain snow in higher
elevations. On Wednesday, the atmospheric river continues moving
northward into central Chile, however, the amount of available
moisture is expected to decrease, meaning the precipitation totals
are expected to be between 15-20mm from the Central Chile region
to Los Lagos. In addition, another frontal boundary with an
occlusion is entering in the Austral region, where expect maxima
of 20-35mm in Aysen and north Magallanes. These low level systems
are expected to have the assistance of short wave troughs and
favoring the advection of vorticity. On Thursday, a ridge axis
enters the region in the mid to upper levels, while in the lower
levels, available moisture decreases as winds enter from the west.
Expect maxima of 15mm in the Austral region of Chile.

In the central portions of the continent, on Tuesday, the
precipitation events are expected to the north, in portions of
central and south Brasil and into north Bolivia. A frontal
boundary is weakening over the Parana Basin and south Pantanal and
extends into Espirito Santo by Tuesday evening, while a secondary
weak stationary front enters the Rio Grande do Sul and Serra
Gaucha region. Expect some weak onshore flow to favor maxima of
20-35mm in Espirito Santo. The regions of north Argentina, Uruguay
and Paraguay are expected to remain relatively dry on Tuesday. On
Wednesday, with the assistance of upper level troughing increasing
the baroclinicity and lowering pressures in north and central
Argentina, the South American LLJ is strengthened, bringing
moisture from the north, as well as favoring troughing in the
lower levels over portions of the Chaco Region, south Paraguay,
and into Rio Grande do Sul in Brasil. As such, from south Paraguay
into the Mesopotamia region of Argentina can expect moisture
convergence along low level troughing, favoring maxima of 30-60mm,
with a moderate risk of severe weather, assisted by the advection
of vorticity and shortwave troughs in the mid levels. Central
Paraguay and portions of Rio Grande do Sul can expect a slight
risk of severe weather and maxima of 15-25mm. On Thursday, the
strengthening of the mid level ridge over central Brasil will
favor interactions at the periphery of the mid level trough to the
south over regions of south Bolivia, north Argentina, Paraguay and
into south Brasil. This interaction will enhance short wave
troughs in the area, favoring the baroclinicity, and thus, the
lower levels will see troughing and potential for increasing low
pressure over the Chaco Region into Central Paraguay. The region
can see increase chances of severe weather, while the low level
jets continue to transport moisture from the north. This will
favor maxima of 35-70mm from south-central Paraguay into Formosa
and Chaco-Argentina. The Chaco region from Bolivia into Argentina,
into Central Paraguay, and the Mesopotamia region of Argentina can
expect maxima of 20-35mm.

To the north, in the tropical regions of South America, troughing
and low level moisture convergence along the easterly trade winds
will interact with the diurnal cycle throughout the forecast
period. On Tuesday, the presence of moisture over the Central
Amazon Basin and into Central Brasil, expect maxima of 20-45mm,
with a potential for locally higher amounts. As the pocket of
moisture continues to propagate west on Wednesday, expect maxima
of precipitation over the western Amazon Basin with amounts of
20-45mm. By Thursday, dry air is being advected over eastern and
central Brasil, while moisture is expected along the foothills of
the Andes from central Peru to south Colombia, where expect maxima
of 20-45mm.

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

Castellanos...(WPC)



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