211
FXUS20 KWBC 151823
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
223 PM EDT Wed Oct 15 2025

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

South American Forecast Bulletin from 15 October 2025 at 1830 UTC

In the higher mid - latitudes...

The axis of an upper level trough is currently traversing the
southern Andes and will be located across southern Argentina after
Wednesday afternoon. In its wake, still expect the sustenance of
an upper level jet streak that will favor jet streak dynamics
through Thursday morning. At the surface, a cold front will begin
to move inland Wednesday afternoon and will be accompanied by
precipitable water values that may exceed 12mm. This subtle
increase in moisture and a favorable upper level regime may yield
total precipitation maxima of 20 - 35mm for Wednesday. Thereafter,
a ridging pattern at all vertical levels will dominate this
region. The interaction between this ridging and the exit region
of a trough, that will be located over the Pacific Ocean on
Friday, will support the development of a surface frontal system.
Ahead of this frontal system, persistent north - northwesterlies
will help drive moisture from the deep tropics into the higher mid
- latitudes. This moisture plume will begin to move into Austral
Chile after Friday afternoon and precipitable water values will
exceed 25mm. Low level wind speeds may exceed 40 knots which may
enhance local and orographic effects.

In the mid - latitudes...

The upper level wind pattern will stay mostly zonal through Friday
evening and wind speeds will be strong. These conditions may
sustain an upper level jet streak and will help in lowering
pressure levels at the surface and favor jet dynamics. During this
period, expect low level moisture transport to extend from the
subtropics and as far south as northern Argentina, where a
stationary front is anticipated to develop starting Thursday
evening. This front will begin to move as a cold front after
Friday evening at the same time as when an upper level shortwave
trough is expected to move into the region. In the mid-levels, a
series of shortwave troughs may propagate across the region,
serving as an additional trigger for the initiation of
precipitation.

From Wednesday Morning through Thursday morning, the region of
interest will be the Mesopotamia region of Argentina and along the
borders with Uruguay, Brasil, and Paraguay. A trough will be
present in this region and an increase in moisture convergence
will begin early Thursday morning. Upper level diffluence may also
positively help enhance upper divergence. These conditions may
yield a total precipitation maxima of 35 - 70mm for Wednesday.
Thereafter, the aforementioned stationary front will continue to
promote moisture convergence. Through Friday morning, the dynamic
region will be primarily influenced by the left entrance region of
a potent upper jet streak. Mid - level shortwave troughs are
expected to develop due to the volatile nature of the upper
levels, adding an enhancement in vertical ascent across northern
Argentina and southern Paraguay. These conditions may favor total
precipitation maxima of 50 - 100mm for this region from Thursday
morning through Friday morning.  The precipitation maxima should
begin to shift northward with the progression of the cold front.
The areas of greatest precipitation impact from Friday morning
through Saturday morning will be the Chaco region, Paraguay, and
extending into southern Brasil. Expect a total precipitation
maxima of 50 - 100mm for parts of the Chaco region and southeast
Paraguay.

In the subtropics...

Across the region, low level troughs and diurnal tropical
convection will be the main driver for precipitation initiation.
In the Amazon Basin, expect a subtle decrease in precipitable
water with passing days. This will lead to a general decrease in
areas with significant precipitation accumulations for the next
three days. The highest precipitation accumulations will occur
across the northwest region of the Amazon, where moisture
convergence will be most favorable. Across the Pacific coast of
Colombia, though moisture will be abundant, low level wind flow
will not be as favorable for moisture convergence. Thus if any
convection does develop, it will be primarily driven by local and
diurnal effects. Otherwise, expect seasonal conditions for the
rest of the region.


For the latest available charts please visit:
https://www.wpc.ncep.noaa.gov/international/sam_day1-3.shtml

Tinoco-Morales...(WPC)



$$