501
FXUS20 KWBC 051853
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
252 PM EDT Fri Jun 05 2026

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

Forecast Bulletin 05 June 2026 at 1900 UTC:

For the next three days, expect an active upper-level pattern
across north-central South America. Currently, there is a
mid-to-upper level shortwave trough crossing Buenos Aires and it
will support surface to low level troughing. The greatest
precipitation chances will occur during the day on Friday and
decrease thereafter as the upper trough continues to exit into the
Atlantic and the moisture content will decrease. By Saturday,
another upper level trough, which currently has an axis near 83W,
will be moving into the continent. Expect the increase in upper
diffluence and divergence across northern Argentina with the
arrival of the upper trough. In the low levels, there will be an
increase in northerly low level winds as well, which will be long
fetch and extend from the deep tropics. This pattern will allow
for the transport of moist tropical air into the mid-latitudes and
subtropics.

A surface cold front will also begin to develop across far
northern Argentina starting late on Saturday after the upper
trough moves east of the Andes. The cold front will enter northern
Paraguay and southern Bolivia on Monday morning. Thus, expect an
increase in precipitation chances starting Saturday afternoon
along the frontal boundary and continuing into Monday. Light
precipitation accumulations are likely for Saturday and moderate
accumulations are likely for Sunday in the vicinity of the frontal
boundary. Along with frontogenesis, cyclogenesis is expected to
begin on Sunday morning. This system will continue moving to the
northeast, moving across the Mesopotamia region of Argentina and
Uruguay from Sunday into Monday. Precipitation chances will
increase in Uruguay after Monday morning as the system moves
overhead.

Other regions being indirectly affected by the aforementioned
upper trough will be the Andean foothills of Bolivia and Peru.
With the decrease in pressure values to the south, there will be
an increase in north-northwesterly low level winds across the
southwest Amazon basin. This will lead to localized orographic
effects and moisture convergence. Overall, daily precipitation
accumulations will be light in this region.

In the tropics, for the next three days, the low level wind regime
will be a significant contributor for precipitation processes. On
Friday, a tropical wave will be arriving in the afternoon, leading
to the increase in moisture convergence and low level cyclonic
rotation. Though, the highest precipitation accumulations will be
confined to the northern coasts of the region. This region will
also see amplified upper divergence due to the presence of upper
diffluence. By Saturday, the tropical wave will be moving into
Guyana and far eastern Venezuela. On Sunday, expect it to be
traversing across central and western Venezuela. Expect an
increase in precipitation chances and daily enhanced total
precipitation maxima in the vicinity of this wave.

Another region of interest is along the Pacific coasts of Colombia
and Ecuador. Expect weak westerly low level winds to continue to
converge into the region, leading to an increase in orographic
effect and moisture convergence. The region will remain moist for
the next three days as well, where precipitable water values will
be exceeding 50mm. Thus, expect daily moderate to enhanced total
precipitation maxima. Note that a low level ridge will also be
developing along the equator, off of the coast of Ecuador. This
will reinforce the increase in northerly low level winds into
Ecuador and far northwestern Peru.

Across the rest of the region, expect multiple low level troughs
and moisture plumes to traverse the region, leading to the
enhancement in moisture convergence. This will yield light total
precipitation maxima for the next three days. Otherwise in
nordeste Brasil, there will be a continuous moist plume converging
into the continent, enhancing moisture convergence. This will lead
to moderate total precipitation maxima as well for the next thee
days. Otherwise, expect seasonal conditions elsewhere.



Tinoco-Morales...(WPC)





$$