South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
234 PM EST Wed Mar 05 2025

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

South America Forecast Bulletin 5 Mar 2025 at 1945UTC:

In Mid - Latitude South America...

In Central Argentina, in the low levels, a strong South America
Low Level Jet (SALLJ) will begin dominating central South America,
helping channel into central Argentina, yielding above average
precipitable water for the next three days. In the upper levels,
speed divergence and upper diffluence will remain favorable ahead
of the passage of an upper trough, which will begin moving across
the Chilean Andes and into west - central Argentina by Wednesday
afternoon. This trough is expected to exit into the Atlantic Basin
by Thursday morning. During this period, anticipate a surface
stationary front to be present across the La Pampa  - Buenos
Aires, south Cordoba - Santa Fe, and east Cuyo provinces. Along
and ahead of this front, low level moisture convergence will be
favorable, yielding to a total precipitation maxima of 25 - 50mm
from Wednesday morning through Thursday morning.

Starting Thursday evening, another slow moving potent upper and
stacked mid level trough will begin to propagate across the
central Chilean Andes. The increase of upper level wind speeds
will also favor the rotation of the atmosphere in the lower
levels, and help induce frontogenesis across central Argentina.
After Thursday evening, expect the development of a fast moving
cold front across central Argentina. By Friday evening, the front
will be across north - central Argentina. Ahead and along the
front, expect an increase in moisture convergence, which is being
enhanced by the SALLJ. These conditions will yield a total
precipitation maxima of 35 - 70mm from Thursday morning through
Friday morning across south - central Argentina with a slight risk
for severe weather. By Friday morning through Saturday morning, a
total precipitating maxima of 30 - 60mm is possible, with a slight
risk for severe weather across central Argentina.

In Chile, at the upper levels, through Thursday evening, expect an
increase in wind speeds, which is associated with a strengthening
upper jet streak that is ahead of a potent upper trough. This will
favor an increase in upper divergence across central Chile through
Thursday evening. At the low levels, a long fetch moisture plume
will continue to impact this region, with winds speeds being
favorably strong through Thursday morning. This moisture plume
will weaken thereafter as it quickly propagates northward. Through
Thursday morning, a total precipitation maxima of 20 - 45mm is
possible. Thereafter on Thursday through Friday morning, the
aforementioned propagating potent upper trough will also be
accompanied by mid - level vorticity advection. A slight increase
in moisture, associated with a weak moisture plume, will enhance
moisture convergence and favor orographic effects on Thursday
evening. These conditions will yield to a total precipitation
maxima of 20 - 45mm from Thursday morning through Friday morning.

In Tropical South America...

In the upper levels, a feature of interest is a broad ridge
resembling the Bolivia High centered at 14S 81W on Wednesday
afternoon. This ridge will favor speed divergence for the next
three days across east Peru and Bolivia. In central Bolivia, a
pre-existing surface trough will persist through Friday morning
and favor an increase in moisture convergence. These conditions
will yield a daily total precipitation maxima of 20 - 45mm.

Another region of interest is Ecuador and Colombia, where at the
upper levels, expect an increase in easterly wind speeds, favoring
speed divergence for the next three days. In the mid - levels, the
wind flow direction will also begin to shift to a more westerly
direction after Wednesday evening. Expect shear after Thursday
morning, limiting the potential for deep convection. In the low
levels, moisture convergence will be most favorable through
Thursday evening, before the wind direction begins shifting to a
more east and west direction. Thus, expect the greatest total
precipitation maxima to occur from Wednesday morning through
Thursday morning, with a maximum of 30 - 60mm possible.

In northeast Brasil, the interaction between the easterly trades
and ITCZ will continue to favor convergence across this region.
Also, series of low level troughs and associated moisture
convergence will further increase precipitation potentials. These
conditions, coupled with upper divergence, will favor daily total
precipitation maxima of 25 - 50mm from Wednesday morning through
Friday morning.

Elsewhere in Tropical South America, the ITCZ and NET will
continue to favor diurnal convection across the region. In the
low, mid, and upper levels, anticipated an overall increase in
easterly winds after Thursday morning, which will favor a
moistening of the atmosphere. For the next three days, expect a
series of low level troughs, accompanied by moisture convergence,
to favor higher precipitation totals across north Brasil and the
Amazon Basin.


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