FXUS20 KWBC 241932

PMDSA 



South America Forecast Discussion - International Desks

NWS Weather Prediction Center College Park MD

331 PM EDT Fri Oct 24 2025



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



South American Forecast Bulletin for 24 October 2025 at 1930 UTC



The main story today is the potential for severe thunderstorms

from northeastern Argentina to southern Uruguay, associated with a

cold front that is moving north, which will encounter a northerly

low-level jet, causing moisture convergence in the lower levels.

This will also combine with favorable mid to upper level dynamics.

Therefore, Strong thunderstorms, probably producing strong winds,

hail and heavy rainfall may be observed ahead of the cold front

today and into the weekend. This frontal boundary will gradually

move north into Paraguay and Bolivia this weekend.



In the upper levels, there is a broad trough extending from the

southeast Pacific and Austral Chile, all the way up to around 20N.

This trough is tilted west, and will move through central to

southern South America this weekend, while a secondary trough

moves in to Austral South America on Sunday, and another shortwave

trough is expected to enter central Chile. The upper levels also

will have a strong jet that will be particularly pronounced over

northeastern Argentina late tonight into early Saturday, into

Uruguay from Saturday into Sunday. This jet will provide

divergence aloft for the development of thunderstorms over the

area.



The mid levels and the upper levels are relatively well stacked

vertically. The same pattern of troughs are suggested in the mid

levels by the model guidance. That said, the mid level jet over

Argentina is forecast to be over Northern Patagonia tonight into

Saturday. Another mid level jet is forecast to be over

northeastern Argentina and Uruguay for Saturday into Sunday. The

latest guidance also suggests that a very strong mid level jet

will be moving in across Austral South America this weekend.



In the lower levels, a series of frontal boundaries moving into

the southern half of South America. In addition, low level jets

across central South America from the north will be observed

today, but these will shift to southerly jets by Sunday. The low

level jets could bring deep moisture from the north that will

interact with the frontal boundaries, providing plenty of moisture

for the expected strong thunderstorms.



The situation across Tropical South America is expected to be

generally influenced by the diurnal and local effects. The mid and

upper levels are, for the most part, dominated by a high pressure.

There is drier than normal air across the eastern portions of

Brasil, but western Brasil will have higher than normal moisture,

as well as Colombia and eastern and northern Peru. This general

setup will favor for the most significant rainfall to occur over

central to western Brasil. However, there is some rain forecast

across the eastern coast of Brasil from around Espirito Santo to

the Brazilian Nordeste today and Saturday, while most of the rain

would be limited to the coast of Bahia on Sunday.



For the latest available charts please visit:

https://www.wpc.ncep.noaa.gov/international/sam_day1-3.shtml



Alamo...(WPC)







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