South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
234 PM EDT Mon Jul 06 2026

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

Forecast Bulletin 06 July 2026 at 1835 UTC:

Across the mid-latitudes...

For the next three days, expect a dynamic upper level pattern
across Chile. Starting on Monday, a frontal boundary will be
moving into southern Chile where it will be accompanied with
strong northwesterly low level winds. This flow will support the
transport of moist air into the region and leading to above normal
precipitable water values. Beginning on early Tuesday morning, an
upper level jet streak max will become orthogonal to the local
topography over southern Chile, favoring the intensification of
divergence in the region. Precipitation chances will be increasing
on Monday with the arrival of the frontal boundary, where enhanced
total precipitation maxima is likely across southern Chile. By
Tuesday, expect elevated precipitation maxima across southern
Chile when the mid-to-upper level dynamic is anticipated to become
more favorable for the development of cumulonimbus. The upper jet
streak max will be exiting east on Wednesday, leading to the
decrease in mid-to-upper level dynamic support across Chile. At
the same time, expect the weakening surface frontal boundary and
accompanying atmospheric river to continue propagating northward
along the Pacific coast of Chile. Thus, expect a gradual decrease
in rainfall accumulations for Wednesday across southern Chile.

On Wednesday, the frontal boundary will re-project into the
north-central Patagonia region of Argentina and the lowering
pressure values associated with the arrival of the upper jet
streak max will support moisture pooling and the development of
mid-level shortwave troughs. These conditions will increase
chances for snow showers across the southern regions and rain
across the northeastern region of northern Patagonia.

Across subtropical South America...

A pre-existing cold front is currently across far southern
Bolivia, Paraguay, and southern Brasil. The frontal boundary will
lose its definition during the day across Bolivia and Paraguay but
will remain intact across southern Brasil for the rest of the
forecast cycle, slowly moving up the Atlantic coast. Precipitable
water values will remain above normal in the vicinity of this
surface feature but daily precipitation accumulations will be
light as the precipitation will be mainly driven by surface and
mid-level processes.

Across the tropics...

A series of low level troughs and tropical waves will be moving
across the region for the next three days that will support the
initiation and sustenance of convection and showers. An important
tropical wave is currently in the vicinity of the Guianas and is
expected to move into eastern Venezuela for Tuesday. By Wednesday,
the tropical wave will be arriving into western Venezuela where it
will also tap with an increasingly diffluent upper level wind flow
pattern. This will lead to the increase in upper divergence in the
region for Wednesday. This region will also be highly unstable,
helping support deep convection. Thus, expect enhanced total
precipitation maxima in the vicinity of this tropical wave for the
next three days. Meanwhile, west of the Ecuadorian and Colombian
Andes, there will be daily moderate total precipitation maxima due
to the presence of high precipitable water values. Local effects
and orographic enhancement will support the initiation of
convection. Across the rest of the tropics, expect daily diurnal
showers and thunderstorms.

Tinoco-Morales...(WPC)