South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
233 PM EDT Mon Jul 13 2026

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

Forecast Bulletin 13 July 2026 at 1835 UTC:

In the mid-latitudes...
For the next three days, expect an active precipitation pattern
across south and central Chile and continuing through the rest of
the work week. For today, an upper jet streak max is continuing to
drive jet dynamics in the region and supporting the sustenance of
a surface frontal system. This frontal boundary is being
accompanied with above normal precipitable water values and
enhanced north-northwesterly low level winds that will support
moisture convergence. The upper jet streak max will be weakening
by Tuesday but an upper trough, which will be located off the
Pacific coast of southern Chile, will continue to support a
frontal boundary in the region for the rest of the forecast cycle.
Also starting on Wednesday, a potent jet streak max will begin to
arrive into the north-central regions of Chile, increasing
divergence.

The presence of above average precipitable water values and
elevated surface convergence along the front will lead to the
increase in precipitation chances in the region. For today, expect
moderate total precipitation maxima across austral Chile, which
will be primarily influenced by the traversal of the occluded
front. On Tuesday, moderate total precipitation maxima is likely
across southern Chile, leading to coast showers and mountain snow.
For Wednesday, there will be an increased risk for cumulonimbus in
the region with the approach of the upper trough and upper jet
streak max in the same region as Tuesday.

Another region of interest is Rio de la Plata for Wednesday. As
the aforementioned upper jet streak max moves into the continent,
expect the development of an upper level trough across northern
Argentina starting Wednesday evening. At the same time, the South
American Low Level Jet (SALLJ) will be present in the region,
helping transport moist tropical air into the region. Severe
thunderstorms are expected to develop during this period as the
region will be very moist and unstable. The upper trough will help
amplify upper divergence in the region. Higher precipitation
accumulations are expected for Thursday.

In the subtropics and tropics...
An upper level trough is expected to migrate along the central
Atlantic coast of Brasil for the next three days and will maintain
a surface cold front. Low level winds will become increasingly
southeasterly with the approach of the cold front, leading to
enhanced surface convergence in the region and orographic effects.
The highest precipitation accumulations will be along the coasts,
with the regions of precipitation interest propagating northward
with passing days. Expect moderate rainfall accumulations in the
vicinity of the frontal boundary. Another region of interest is
the northwest Amazon. A mid-level ridge will be developing across
north-central Brasil and will enhance easterly low to mid-level
winds into the region. Expect the highest precipitable water
values to be present in this region as well. The presence of low
level troughs and tropical waves will also support the daily
development of showers and thunderstorms across the region.
Meanwhile across the Peruvian jungle, expect the development of
daily showers and thunderstorms that is being supported by the
transport of moisture and locally induced surface convergence.


Tinoco-Morales...(WPC)