436
FXUS20 KWBC 111805
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
205 PM EDT Thu Jun 11 2026

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

Forecast Bulletin 11 June 2026 at 1805 UTC:

In Chile...

An upper level jet streak max is currently propagating over
southern Chile and is expected to be present in this region
through Friday afternoon. During this period, the jet streak max
will be perpendicular to the orography and coastline. Anticipate
enhanced divergence with this feature for Thursday and Friday. In
the low-to-mid levels, there will be a closed low pressure system
that will also be supporting a surface frontal system. Meanwhile,
precipitable water values will continue to increase through the
day on Thursday and this moisture plume will be accompanying the
frontal boundary. For Thursday, expect the cold front to converge
into Aysen and Los Lagos during the day and for it to continue
moving across the southern Chile region on Friday. The cold front
will lose propagation speed and will transition into a stationary
front once it reaches the state of Biobio. This stalling is being
influenced by a semi-zonal mid-to-upper level wind flow and the
presence of a slow moving mid-to-upper trough west of the region.
The day with the greatest precipitation impact will be on
Thursday, when the mid-to-upper level dynamic will be the most
favorable for ascent and divergence. Expect enhanced total
precipitation maxima across Aysen and Los Lagos for this period.
For Friday, a moderate total precipitation maxima is likely in
Biobio and Araucania, which is where the frontal boundary will be
located. Thereafter, the precipitable water values will decrease
with the weakening of the long fetch moisture plume and it will
lead to a decrease in precipitation accumulations.

In central South America...

Another region of interest is south Brasil and Paraguay. In the
upper levels, a positively tilted upper trough, that is embedded
within the subtropical and polar upper jet streams, will support
jet streak maxes along its exit regions. Though, the polar upper
trough will lose definition during the day. These two features
will move eastward in tandem and will enhance upper divergence
from Paraguay through the south Brasil/Uruguay border. In the
mid-levels, the trough embedded with the subtropical jet stream
will be over south Brasil. The axis of the mid-level trough will
be exiting the continent starting on Friday night. Thus, between
Thursday and Friday night, expect enhanced divergence in the
region and for the destabilization of the vertical column, leading
to increasing chances of severe weather. At the same time, a broad
ridging pattern will be present across north-central Brasil, which
will support the transport of moist tropical air into the
subtropics. Precipitable water values will thus be above normal
across much of the region for the next three days.

At the surface, expect the development of a surface frontal
boundary for Thursday afternoon. On Thursday evening, a cold front
will be located from central Bolivia, extending across Paraguay,
and southern Brasil, though the cold front will quickly lose its
definition across Bolivia on Friday. Starting Friday afternoon,
the propagation speed of the cold front will increase and it will
begin propagating northward across Brasil. On Friday evening, the
cold front will be located across the Pantala and Parana basin
regions of Brasil and Serra do Mar. By Saturday, the front will
still be traversing the northern coastline of Serra do Mar. To the
west, the enhancement in southerly low level winds will debilitate
the frontal boundary and thus disorganize its structure. Also
Saturday, another low level trough will be developing over
center-west Brasil with the arrival of a shortwave mid-to-upper
level trough embedded within the polar jet stream. This will lead
to an increase in precipitation chances across Pantanal and Parana
Basin regions of Brasil.

With respect to precipitation accumulations, the period with the
greatest precipitation impact will be on Thursday when the
mid-to-upper level regime will be most favorable for ascent and
divergence. Enhanced total precipitation maxima are likely in Rio
do Sul and Serra Gaucha. Thereafter, expect moderate total
precipitation maxima in the vicinity of the front. Meanwhile along
the low level trough in Paraguay/center-west Brasil, expect
moderate total precipitation maxima.

In the tropics...

Expect the traversal of low level troughs and tropical waves for
the next three days. These features will provide cyclonic
circulation and moisture convergence, yielding an increase in
precipitation chances. Meanwhile along northern Guianas, the
proximity of the Intertropical Convergence Zone (ITCZ) will
continue to support the traversal of moisture plumes and troughs.
Expect daily light to moderate total precipitation maxima for the
next three days in this region in association with the ITCZ.

Off the coast of Colombia and northern Ecuador, northwesterly
winds at upper levels are dominating and are being influenced a
closed cyclonic system located between Ecuador and Peru; the
trough axis will be across the Amazon region and will be
converging with an upper ridge extending from eastern Brazil on
Thursday. Starting on Friday evening, expect a shift to upper
level winds from the north over northwestern South America, which
will be accompanied by areas of upper divergence in the Amazon
regions of Ecuador and Peru and much of Colombia. At mid- and
low-levels, the wind is predominantly easterly, transporting
higher moisture content into Colombia and northern Ecuador; this
will generate an increase in precipitation accumulations for
Friday and Saturday, particularly across the Amazon and coastal
areas of Colombia, as well as northern Ecuador and mountainous
zones.


Tinoco-Morales...(WPC)
Macas...(INAMHI)




$$