South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
316 PM EDT Wed Jul 08 2026

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

Forecast Bulletin 08 July 2026 at 1920 UTC:

A series of frontal boundaries will be moving across austral and
southern Chile for the next three days. The first frontal boundary
is already moving across the region and is being accompanied by
moderate total precipitation maxima. Across austral Chile, there
will be a gradual decrease in precipitable water as an occluded
front moves into the continent. Meanwhile, a weakening atmospheric
river will be accompanying the cold front that will affect
southern Chile for Wednesday. At the same time, a mid-level trough
is moving overhead and is expected to move east of the Andes and
into north-central Patagonia during the day on Wednesday. There
will be vorticity advection with this system in Patagonia as well.
As the frontal boundary moves across the Andes, it will re-project
into Argentina. These conditions will favor broad low level
circulation in the region that will support precipitation
processes. Thus, expect enhanced total precipitation maxima across
southern and austral Chile for Wednesday and the chance for rain
and snow in Patagonia, where precipitation maxima will be
moderate.

On Thursday, another frontal boundary will be moving into the
region. An upper jet streak max will also be present in the region
that will support upper divergence. Expect precipitable water
values to approach 30mm for this period. Thus, expect moderate to
enhance total precipitation maxima on Thursday. On Friday, the
frontal boundary and accompanying atmospheric river will be
weakening, leading to a reduction in total precipitation maxima in
the region.

Another region of interest is southern Brasil and Paraguay for
Thursday and Friday. Currently, there is uncertainty in the
development of precipitation across the region. An upper level
trough will be amplifying across the region starting on Thursday,
which will support the decrease in surface pressure levels in the
region. However, there is model inconsistency in the magnitude of
the amplitude of the upper level trough. A more amplified upper
level trough (ECMWF) will support the development of a weak
frontal boundary in the region while a less amplitude solution
(GFS) will support the development of a low level trough.
Regardless, surface to low level cyclonic circulation will be
present in the region for the end of the forecast cycle. Global
models are also disagreeing on the moisture content in the region,
with the ECMWF a more moist solution and thus higher totals.
Overall, expect precipitation chances to increase for Thursday and
Friday.

Across the tropics, the propagation of tropical waves and low
level troughs will continue to maintain daily showers and
thunderstorms across the Guianas, Venezuela, and Colombia. Expect
moderate total precipitation maxima in the vicinity of these
features. Another region of interest is the Pacific coasts of
Colombia and Ecuador. The presence of the Caribbean low level jet
is helping support the increase of northerly low level winds into
the Pacific, which will also be interacting with an enhanced
southerly low level wind and leading to zones of low level
convergence across Colombia for Wednesday and Thursday. At the
same time, the passage of tropical waves across the Caribbean Sea
will support the increase in low level cyclonic circulation across
the Pacific. Meanwhile, the environment will remain moist for this
period as well. Thus, expect enhanced total precipitation across
Colombia and Ecuador for the next three days. Though, there will
be a slight decrease in precipitation accumulations for Friday as
the low level convergence and orographic effects decrease across
Colombia. However, still expect prevailing and weak westerly low
level winds with the development of a low level ridge off the
Pacific coast of Ecuador.


Tinoco-Morales...(WPC)