959
FXUS20 KWBC 101917
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
317 PM EDT Thu Sep 10 2026

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

Forecast Bulletin 10 September 2026 at 1915 UTC:

Over the next three days, there is an enhanced chance of
significant rainfall across portions of southeastern Brasil and
portions of northeastern Argentina. At times, strong thunderstorms
could be expected across the aforementioned region. The rest of
Brasil is expected to observe generally benign weather, though
some isolated thunderstorms are possible across western Brasil
this afternoon and evening (Thursday). Showers and a few
thunderstorms are forecast across portions of Bolivia on Friday
and Saturday, but the storms are not expected to be as strong as
the ones expected in Brazil, they will also be relatively short
lived.

A high pressure ridge in the lower levels will keep most of
eastern to central Brazil relatively dry for the next few days.
This will also cause the SALLJ to develop and provide good
moisture to southeast Brasil. The low level winds will then shift
to a southerly  direction across central South America Friday and
Saturday, causing moisture to pool and increase the chances of
rain over Paraguay and Bolivia in the coming days.

Considering this moisture advection and pooling in the lower
levels, it is also worth mentioning that the mid and upper levels
will be conducive for thunderstorm development across the
southeast portions of Brasil. Everything will work together to
provide this persistent environment for thunderstorm development
over the area. This is due to a trough in the mid and upper
levels, along with a jet, providing ventilation and divergence in
the area. The mid level trough will bring cooler than normal mid
level temps to the area, which will also increase the chances of
hail.


Much more benign weather is expected across Chile and the
mountains of Argentina. There is some moisture moving in, but the
impact is expected to be mainly that of light to moderate rain
with mountain snow in some areas. The rain is expected to remain
mainly in the order of 15mm or less, with then some mountain snow
across central and southern Chile.


Alamo...(WPC)





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