362
FXUS20 KWBC 141929
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
228 PM EST Fri Nov 14 2025

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

South American Forecast Bulletin for 14 November 2025 at 1930 UTC

On Friday, the area of interest is expected over the tropical
region of South America, as large amounts of available moisture
are expected over the west and central portions of the Amazon
River Basin. The active transport of moisture in the easterly
trade winds are accompanied by embedded low level troughs, and
these will be impacted by the diurnal cycle on Friday. Even though
the South American Low Level Jet (SALLJ) is not present, this
moisture will interact with the Andes Mountain regions of Ecuador,
Peru, and north Bolivia. Orographic lift will favor maxima of
30-60mm in north-central Peru, while a trough over the central
Amazon Basin will favor similar maxima. From north Bolivia into
east Peru expect generalized maxima of 20-45mm. In the central
portions of the continent, some of the moisture from the tropical
region remains and with the remnants of a frontal boundary favor
generalized maxima of 20-45mm from Chiquitania-Bolivia to east
Paraguay and portions of the south Pantanal region in Brasil. In
the southern cone of the continent, the upper level Polar Jet is
entering Austral Chile, and with it a lower level frontal boundary
and a weakening atmospheric river with precipitable water values
exceeding 25mm. The exit region of the jet will favor upper level
support, while the orographic lift expected along the Austral
region of Chile will favor for moderate precipitation ranging from
20-45mm in south Aysen and north Magallanes.

On Saturday, an upper level trough from a cutoff low enters Chile
and Argentina by Saturday afternoon, and its divergent side
becomes enhanced as it is associated with an upper level jet to
the south over the Patagonia region. The increased divergence
aloft will provide ample ventilation from Saturday afternoon
through Sunday morning over regions of the La Pampa, through
Cordoba and into the southern Mesopotamia region of Argentina. As
the divergence increases aloft, convergence in the lower levels
will favor the return of the SALLJ from central Bolivia into
Argentina, and with it transporting moisture from the tropical
region into central Argentina. Additionally, this will favor
frontogenesis over Cordoba/Santa Fe. Just to the south, the
frontal boundary that entered Chile on Friday, will propagate into
the north Patagonia region, interacting with the moist air mass to
the north. With these conditions present, the central regions of
Argentina and into Uruguay will see increased risk of moderate
severe weather from Saturday into early Sunday morning. In terms
of precipitation, the northwestern Rio de la Plata region, and
central La Pampa/Buenos Aires region can expect maxima of 30-60mm.
In southern Brasil, the presence of shortwave troughs in the mid
to upper levels, plus the remnants of frontal boundaries, now low
level troughs and the entrance of increased moisture in the region
will favor generalized maxima of 20-45mm along the southern Parana
Basin and into the Serra do Mar region. In the northern regions of
the continent, the moisture advected in the easterly trade winds
continues to interact with the terrain along the Andes Mountains
expect maxima of 20-35mm in Peru, while Amazonas-Brasil can expect
maxima of 15-25mm.

On Sunday, the upper level trough has now pushed northeastward,
with its base in central Bolivia and south Peru, however, this has
enhanced the interaction with the periphery of the upper level
ridging in central Brasil, providing an area of increased
divergence and diffluence from south Bolivia, through Paraguay,
and into south Brasil. The forming frontal boundary is quickly
propagating into north Paraguay and Rio Grande do Sul-Brasil,
interacting with the moisture from the tropical region of the
continent. While the secondary frontal boundary to the south is
expected over north Argentina and over the border region between
Uruguay and Brasil by Sunday evening. The interaction between
these elements will favor a risk of moderate severe weather from
Paraguay through south Brasil, while also favoring deep convection
in the evening of Sunday into early morning hours of Monday. The
northeast Chaco region can expect maxima of 60-125mm with a
possibility of higher total precipitation. The south Pantanal
region can expect maxima of 40-80mm, with potentially higher
amounts. From central Paraguay to Rio Grande do Sul expect maxima
of 30-60mm. In the surrounding regions to the west, along the
Andes Mountains from Bolivia and Northwest Argentina expect
generalized maxima of 20-45mm. In central Bolivia, the moist
transport and SALLJ interacting with the Andes, and the divergence
aloft available for ventilation will favor deep convection and a
potential for maxima ranging from 40-80mm. To the south, a potent
jet streak associated with the western side of the upper level
trough has entered southern Chile. This will enhance the
divergence in the region, while a potent atmospheric river with
strong winds in the lower levels enters Austral Chile, with
precipitable water levels exceed 35mm. This will favor enhanced
orographic lift along the region, and heavy precipitation with
maxima of 40-80mm, with mountain snow from Los Lagos to north
Magallanes. In south Magallanes, expect maxima of 20-35mm.

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

Castellanos...(WPC)


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