South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
255 PM EDT Tue Jul 14 2026

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

Forecast Bulletin 14 July 2026 at 1900 UTC:

In the mid-latitudes...
A surface frontal boundary, with a cold and warm extension, is
currently moving into southern Chile and is being accompanied by
strong low level north-northwesterly wind speeds and precipitable
water values reaching 30mm. The cold front will remain in the
region for Wednesday and by late Thursday evening, another frontal
system will begin to move into the continent. Note that the front
will extend as far south as the Aysen-Los Lagos region by the end
of the day on Thursday with the accompanying surface low pressure
system moving into this region. Though, the higher precipitable
water values will remain across central Chile. For Thursday,
precipitable water anomalies will be over two standard deviations
above normal across north and central Chile.

These frontal boundaries and low level patterns are being
supported by a very dynamic upper level pattern. Currently, there
is a semi-stationary broad mid-to-upper level troughing pattern
off the Pacific coast of southern Chile. Multiple shortwave
troughs will be embedded within this upper trough. The first
shortwave trough is expected to develop a negative tilt during the
day on Tuesday, leading to a further enhancement in upper
divergence across central Chile. Expect the passage of another
upper level shortwave trough for Wednesday. By Thursday, the upper
trough will gain an eastward propagation speed as an approaching
and potent subtropical upper jet streak max begins to move into
northern Chile. This upper trough will remain off the coast of
Chile for the rest of the work week, continuing to elevate
divergence in the region.

The aforementioned conditions will yield elevated precipitation
maxima for the next two days across southern Chile. By Thursday,
there will be an uptick in precipitation accumulations across
Aysen and Los Lagos due to the presence of the low pressure system
and the general increase in precipitable water values. Expect
enhanced total precipitation maxima in this region. The highest
precipitation accumulations are expected for central Chile,
extending as far north as 30S.

With the arrival of the potent jet streak max into the continent,
anticipate the undulation of the upper level wind flow downstream,
particularly over the Rio de la Plata region. Starting on
Wednesday and continuing through Friday, expect the daily
development of upper level shortwave troughs in the region. The
increase in the mid-to-upper level wind speeds will also lead to a
drying trend across the leeward foothills of the Andes (Argentina,
Bolivia) due to the enhanced subsidence in the region. Meanwhile
in the low-to-mid levels, a broad ridging pattern is currently
present across southern Brasil that is supporting the sustenance
of the South American Low Level Jet. This pattern is contributing
to an increase in moisture transport into the Rio de la Plata
region. With the development of the upper level shortwave troughs,
there will also be an increase in moisture pooling in the region,
yielding precipitable water values of up to 30mm. Starting early
Friday morning, expect the intensification of a surface low
pressure system and the presence of a frontal boundary. With
respect to precipitation, expect an increase in light showers and
thunderstorms across Rio de la Plata after Wednesday afternoon and
widespread showers and thunderstorms for Thursday in the same
region.

In the subtropics and tropics...
A cold front will continue to slowly propagate along the coast of
Bahia for Tuesday and is anticipated to lose its definition on
Wednesday; though, its remnants will continue to impact the
precipitation pattern in the region. This cold front is being
accompanied by an upper level trough that will support upper
divergence for Tuesday. The trough axis will begin moving into the
Atlantic during the day on Tuesday and its direct effects will
decrease in the region. Thereafter, expect a low level ridge to
develop off the coast of central Brasil, which will support
onshore (easterly) wind flow and the transport of moisture into
the coasts of Bahia and Espirito Santo for Wednesday and Thursday.
With respect to precipitation, expect the development of showers
and thunderstorms in the vicinity of the front and its remnants
for the next three days, where precipitation accumulations will
remain on the moderate side. By Wednesday, there will be an
increase in isolated showers and thunderstorms across the coast of
Bahia where light precipitation accumulations are likely.

Another region of interest is Venezuela, Colombia, and the
northwest Amazon. A tropical wave is currently moving across
Venezuela and is expected to cross the Andes by the evening today.
Expect an increase in instability and moisture with the passage of
the wave. At the same time, there is a ridge located over the
central Amazon that is promoting easterly low level winds to the
north. This wind direction will help transport moisture into the
region and will be persistent through the rest of the forecast
cycle. These conditions will yield enhanced moderate precipitation
maxima across Colombia and Venezuela for Wednesday. Thereafter,
expect daily light accumulations in the region, especially in the
vicinity of low level troughs and surface convergence zones.




Tinoco-Morales...(WPC)