South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
1220 PM EST Thu Mar 06 2025

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

South America Forecast Bulletin 6 Mar 2025 at 1730UTC:

In Mid - Latitude South America ...

In Central Argentina, in the mid - levels, the South America Low
Level Jet (SALLJ) will continue to dominate across south - central
South America through Saturday morning, assisting in the increase
of available moisture across the region. In the upper levels, a
strong jet streak will affect south - central Argentina through
Friday morning, helping sustain a surface stationary front across
La Pampa - Buenos Aires provinces, Sierra Cordoba, and northwest
Argentina. An increase of moisture convergence along this trough
will favor a total precipitation maxima of 50 - 100mm from
Thursday morning through Friday morning across La Pampa - Buenos
Aires provinces.

After Friday morning, a slow moving potent upper trough will begin
to traverse the region and will exit into the Atlantic Basin by
Sunday afternoon. This trough will support the enhancement of
upper divergence and help induce frontogenesis. Along and ahead of
the cold front, anticipated an increase in moisture convergence,
which is being assisted by the SALLJ. Starting Friday evening,
expect the development of a fast moving surface cold front across
Cuyo and La Pampa - Buenos Aires provinces. A total precipitation
maxima of 35 - 70mm and a marginal risk for severe weather are
possible during this period. By Saturday evening, the front will
be located across northwest Argentina into south Brasil. Expect a
total precipitation maxima of 50 - 100mm across the Chaco region.
A total precipitation maxima of 25 - 50mm is possible in north
Argentina during the same period of time. Across Rio de la Plata,
a total precipitation maximum of 20 - 45mm is possible.

In central Chile, the period of greatest precipitation impact is
Thursday morning through Friday morning. In the upper levels, a
strengthening upper jet streak will continue to propagate across
the area through Friday morning, followed by the passage of a
potent upper trough. In the mid - levels, vorticity advection will
be most favorable Friday afternoon and evening. At the low levels,
a weakening north moving long fetch moisture plume will mainly
impact central Chile through Thursday afternoon. These conditions
will yield to a total precipitation maxima of 20 - 45mm from
Thursday morning through Friday morning. Thereafter, a subtle
increase in moisture, associated with a weakening surface low
pressure system, will impact central Chile briefly from Friday
morning through the evening. This will yield to a total
precipitation maxima of 15 - 25mm from Friday morning through
Saturday morning. Note, another long fetch moisture plume is
anticipated to impact central Chile after Sunday morning,
supporting higher total precipitation maxima.

In Tropical South America ...

In the upper levels, a feature of interest is the broadening of
the Bolivian High, with an axis of 18S 71W on Thursday afternoon.
Another feature of interest is a weakening trough, with an axis at
10S 59W and 20S 55W on Thursday afternoon, through Saturday
afternoon, favoring speed divergence across Bolivia. Thereafter,
the aforementioned mid - latitude potent upper trough will help in
the development of another trough across south - central Brasil.

An area of interest is Bolivia. From Thursday morning through
Saturday afternoon, the main driving force for precipitation
initiation is the speed divergence associated with the Bolivian
High, a stationary low level trough, and enhanced moisture
convergence. These conditions will favor a total precipitation
maxima of 25 - 50mm from Thursday morning through Friday morning
and a total maxima of 20 - 35mm from Friday morning through
Saturday morning. By late afternoon Saturday, an incoming surface
cold front accompanied by enhanced moisture convergence will begin
to enter northwest Paraguay and south Bolivia. This may yield a
total precipitation maxima of 50 - 100mm from Saturday morning
through Sunday morning in south Bolivia. In central Bolivia, an
increase in moisture and northwest low level winds will also
support orographic effects, yielding to total precipitation maxima
of 20 - 45mm for this same time period.

Elsewhere in Tropical South America, the ITCZ and NET will
continue to drive diurnal convection where conditions are
favorable. Through the next three days, upper level divergence, a
series of low level troughs and an increase in moisture will
continue to yield to higher total precipitation maxima. Across
northeast Brasil, the period of greatest precipitation impact will
be Thursday morning through Saturday morning, when stronger
moisture plumes will be traversing across this region. Expect a
daily total precipitation maxima of 20 - 40mm.


Tinoco - Morales...(WPC)
Ledesma...(WPC)