South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
228 PM EDT Thu Jul 16 2026

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

Forecast Bulletin 16 July 2026 at 1835 UTC:

A dynamic upper level pattern will be supporting the development
and sustenance of multiple surface frontal boundaries that will be
converging into central and southern Chile. On Thursday, expect
the arrival of a cold front into central Chile and an occluded
front into southern Brasil. This frontal system will be
accompanied with a moderate intensity atmospheric river that will
contain precipitable water values that will reach 30mm. Also
anticipate strong low level winds from a north-northwest
component. A secondary cold front, with a weaker gradient, will be
moving into Chile during the day on Saturday. Expect a decrease in
precipitation across south-central Chile by Saturday afternoon as
the cold front moves inland. Meanwhile, the now weakened
atmospheric river will shift northward into north-central Chile
and is expected to meander in this region through Saturday before
losing its definition. Thus, expect elevated total precipitation
maxima for Thursday across central Chile and a decrease thereafter
across the south-central regions. In the north-central regions,
there will be ongoing precipitation through Saturday. Note that
precipitaiton will extend as far north as southern Atacama. There
will be a brief lull in precipitation activity on Saturday. By
late Saturday evening and into Sunday, expect the resurgence in
precipitation chances as another frontal boundary will be
approaching the region.

 In the upper levels, expect enhanced upper divergence across
central and southern Chile that is being sustained by the
interaction between a weakening upper trough and a potent upper
jet streak max. The jet streak max will be embedded within the
subtropical jet and is expected to continue converging into
northern Chile. The jet streak max will be supporting the
development of upper level shortwave troughs across northern
Argentina and Uruguay for the next three days and starting on on
Saturday, the upper level wind speeds are projected to increase
across the region as the jet streak max will begin to extend east
of the Andes. This will lead to a dynamic surface to mid level
response in the region. A series of frontal boundaries will be
developing across northern Argentina and Uruguay. However, the
period with the greatest precipitation impact is expected for
Friday and Saturday. There will be multiple shortwave troughs
moving across the region that will help further destabilize the
environment and enhance ascent in the region. There will be a risk
for severe weather in the region as a result. Note that a broad
ridging pattern across the subtropics will help sustain the South
American Low Level Jet (SALLJ) that will continue to transport
moist air into the region. Additionally, moisture pooling along
the frontal boundary will further enhance moisture convergence. 

A low to mid level ridging pattern will be present across the
western tropical region that will support the transport of
moisture into the western Amazon. The presence of tropical waves
and low level troughs will support the initiation and sustenance
of convection across the region. Expect moderate precipitation
accumulations in the vicinity of these systems for the next three
days. Otherwise, daily diurnal showers and thunderstorms will
occur across the entire region for the next three days.



Tinoco-Morales...(WPC)