South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
201 PM EDT Fri Jun 12 2026

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

Forecast Bulletin 12 June 2026 at 1802 UTC:

Across Chile...

A frontal boundary will continue to converge into southern Chile
on Friday and its structure is anticipated to weaken on Saturday.
This frontal boundary is accompanied by a long-fetch moisture
plume that will contain precipitable water values of up to 30mm.
In the low levels, the wind speed will be weakening during the
day, but the direction will remain from the west and northwest,
which will continue to support the transport of moisture into the
region. The precipitation will be primarily driven by the surface
and low level regimes. Thus, the greatest precipitation impact in
southern Chile is expected for Friday. By Saturday, precipitation
impacts will be confined to the higher elevations. Fair conditions
will return for Sunday across southern Chile.

Across the southern austral region of Chile, there will be a
series of surface frontal boundaries moving into the continent
starting on Saturday and continuing into Sunday. There will be an
increase in precipitable water values as well during this period
and low level wind speeds will be exceeding 40 knots through the
weekend. This pattern is being influenced by the presence of a
surface-to-upper level ridging pattern off the Pacific coast of
austral Chile. At the same time, an upper level jet streak max
will be developing overhead and will enhance upper divergence.
Meanwhile in the mid-levels, two shortwave troughs will be
traversing the region and they will be accompanied with vorticity
advection. Thus, moderate total precipitation maxima will be
likely in this region for Saturday and Sunday.

Across Central South America...

An eastward propagating upper trough currently has its axis
entering Brasil. An upper jet streak will be present across its
exit region and it will favor the enhancement of divergence in the
region. The axis of this trough will be exiting the continent on
Saturday afternoon. During this period, expect the presence of a
surface frontal boundary. On Friday, a cold front will be across
southern Brasil. At the same time, there will be an increase in
northerly low level winds along the eastern Andean foothills,
which will lead to the weakening of the frontal boundary structure
in that region for Friday, transitioning briefly into a warm
front. However, by Saturday, a new cold front will develop across
southern Bolivia and northern Paraguay, though its lifespan will
be brief. Once the front arrives into the central regions of
Bolivia on Sunday, its structure will weaken. Meanwhile, the
pre-existing frontal boundary in Brasil will transition into a
meandering stationary front for Saturday and Sunday, being located
across Serra do Mar and Espirito Santo.

With respect to precipitation impacts, on Friday, in the Pantanal
region, a mid-level shortwave trough will be propagating across
the region, providing an enhancement in ascent. Meanwhile, there
will also be an increase in moisture convergence along the
transitioning front. Expect moderate total precipitation maxima in
this region for Friday. Meanwhile along Rio Grande do Sul, there
will be moist onshore flow being supported by an occluded front
off the coast. Expect the development of showers during the day on
Friday and moderate total precipitation maxima through Saturday
morning. By Saturday, another mid-to-upper level shortwave trough
will be moving across the Pantanal region and the Parana Basin. At
the same time, there will be an increase in precipitable water
values along the frontal boundary, which will yield enhanced total
precipitation maxima. By Sunday, expect a decrease in total
precipitation maxima in the region. Another region of interest is
south-central Brasil for Friday , where mid-level confluence will
be present in the low levels, helping support moisture pooling. At
the same time, a low level trough will be developing, further
enhancing cyclonic rotation. This will yield a total precipitation
maxima of 15 - 25mm for Friday.

In Tropical South America...

Meanwhile in the western tropics, there will be an increasing
mid-to-upper level ridging pattern for the weekend. By Sunday, a
mid-level ridge will be centered over east-central Bolivia. This
pattern will support the transport of moisture into the southwest
Amazon Basin and the overall increase in northerly low level winds
into Bolivia and Peru. Also for Saturday and Sunday, expect an
increase in easterly low-to-mid level winds in eastern Colombia,
Ecuador, and northeastern Peru. This will support the transport of
moisture into the high terrain and thus assist in the increase in
precipitation. Enhanced total precipitation maxima are likely in
this region for the weekend. Meanwhile in southern Peru and along
the eastern foothills of the Andes in north and north-central
Bolivia, expect light to moderate total precipitation maxima for
the next three days.

Along the Pacific coasts of Colombia and Ecuador, expect a gradual
increase in precipitable water values, though the low level winds
speeds will be on the weaker side. Meanwhile along the southern
coast of Ecuador, expect an increase in southerly low level winds
that will help confine the highest precipitable water values to
the north and north-central coasts of Ecuador. Expect moderate
total precipitation maxima for the next three days in this region.
Another area of interest is the Guianas where daily showers and
thunderstorms will develop, primarily being influenced by the
presence of the Intertropical Convergence Zone (ITCZ) and the
propagating of Tropical Waves and low level troughs. The highest
precipitation impacts will stay confined to the northern coasts of
the Guianas for the next three days.


Tinoco-Morales...(WPC)