FXUS20 KWBC 092009
PMDSA 

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
308 PM EST Fri Jan 09 2026

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

South American Forecast Bulletin for 09 January 2026 at 2010 UTC

On Friday, severe weather is expected in the central portion of
the continent with the presence of an upper level short wave
trough crossing north Argentina on Friday into Saturday. The upper
trough is interacting with the Bolivian High to its north, where
enhanced winds are favoring the development of a jet stream in the
eastern side of the trough, as well as favoring the trough to tilt
negatively over north-central Argentina. This will create enhanced
divergent conditions aloft, fueling deep convection and heavy
precipitation to the east, from the Chaco region into Uruguay and
south Brasil. These conditions aloft are enhancing the
cyclogenesis over Uruguay, as well as, frontogenesis over Uruguay
by Friday evening. With the influx of moisture due to the South
American Low Level Jet, expect maxima of 60-125mm over Uruguay
into Rio Grande do Sul and into northern portions of the
Mesopotamia region of Argentina. In the rest of the Mesopotamia
region and into West Uruguay, expect maxima of 40-80mm. These
regions can expect moderate risk of severe weather throughout the
forecast day. To the north, the Bolivian High continues to extend
over much of the region, extending into central Brasil and the
northern Amazon Basin. Expect moderate precipitation over the
region on Friday.

On Saturday, conditions will continue similar to Friday, in
addition to the Cavado do Noreste retrograding into central
portions of Brasil, favoring drier conditions on Saturday in early
Sunday. To the south the upper level shortwave trough continues to
propagate eastward into east Argentina and Uruguay, favoring
divergent conditions aloft over Paraguay and south Brasil. The
presence of moisture from the north will continue to favor heavy
precipitation over the region, with maxima reaching 40-80mm in
portions of the region. In southern Chile, the entrance of various
frontal boundaries will favor trace to light amounts of
precipitation in the Austral region of the country due to a lack
of moisture.

On Sunday, expect the upper level trough in the central portions
of the continent to exit into the south Atlantic Ocean, while its
divergent section begins to exit the region, with the exception of
the northern divergent portion entering south-central Brasil by
Sunday evening. With this set up, expect a decrease in the
enhancement of deep convection in south Brasil, but moderate
precipitation is still expected to extend along a weakening
frontal boundary over south Brasil, as a response to the departing
upper level trough. In addition, a decrease in the transport of
moisture from the north is expected with the absence of the SALLJ,
and thus favoring a decrease in precipitation on Sunday into
Monday. The moisture continues over the western Amazon Basin,
where expect moderate precipitation from south Colombia, along the
western Amazon Basin, and into north Bolivia and the Yungas
region. In southern Chile, similar conditions are expected in the
Austral region as a new frontal boundary is expected to enter by
late Sunday into early Monday, but total precipitation is expected
to remain below 15mm with a chance of mountain snow.

Castellanos...(WPC)


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