South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
230 PM EST Fri Feb 28 2025

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

South America Forecast Bulletin 28 Feb 2025 at 1930UTC:

In Mid - Latitude South America...

In central Argentina and south Uruguay, in the upper levels,
starting Friday morning, an upper shortwave trough will traverse
across the region, exiting into the Atlantic Basin by Friday
evening, helping enhance upper divergence during this period.
Thereafter, an increase in upper level wind speeds is anticipated
and will favor speed divergence through Monday morning. Note, the
acceleration in the upper flow is likely due to the interactions
between an upper trough across south Brasil, formation of the
Bolivian High, and the formation of an upper ridge in the
Atlantic. This flow will favor the formation and propagation of
mid - level shortwave troughs and the maintenance of meandering
surface troughs. In the low levels, the South American Low Level
Jet (SALLJ) will continue to influence the transport of moisture
into this region through Monday morning, favoring moisture
convergence during this period. The SALLJ will begin to weaken
thereafter due to increasing subsidence associated with the upper
trough across south Brasil. From Friday morning through Saturday
morning, a total precipitation maxima of 20 - 45mm is likely
across La Pampa - Buenos Aires and a maximum of 20 - 35mm in Rio
de la Plata, where a marginal risk for severe weather is possible
in these regions. Note, convection may be most favorable during
Friday. Another period of interest will be Sunday morning through
Monday morning. On Sunday, mid - level vorticity advection will be
most favorable, yielding to a total precipitation maxima of 30 -
60mm accompanied with a marginal risk for severe weather across
the La Pampa - Buenos Aires region.

In Chile, a series of upper troughs and jet streaks will continue
to drive the upper level dynamic regime. Surface fronts
accompanied by moisture plumes will continue to enhance moisture
convergence and orographic effects across southern Chile, yielding
to higher total precipitation maxima in this region through Sunday
morning. From Sunday morning through Monday morning, a potent
upper trough, increasing mid - level vorticity advection, an
increase in low level moisture convergence, and increasing wind
speeds will enhance orographic effects across the region. These
conditions will favor a total precipitation maxima of 15 - 25mm
with a risk for thunderstorms.

In Tropical South America...

In the upper levels, a feature of interest is a potent upper
trough that has an axis at 17S 45W on Friday afternoon. Its axis
is expected to be at 20S 54W by Sunday evening and will likely
lose its definition thereafter. Elsewhere, ongoing convection
across Bolivia will be a contributing factor to the formation of
the Bolivian High by Sunday morning, when its an axis will be
located at 15S 71W. After Sunday morning, the interaction between
these two features will enhance upper diffluence across the north
- central Brasil, yielding to a total precipitation maxima of 25 -
50mm from Sunday morning through Monday morning.

In Bolivia, a mid - level trough will develop across central
Bolivia on Friday and weaken by Saturday morning. Also during this
period, expect an increase in low level moisture, yielding to a
total precipitation maxima of 30 - 60mm from Friday morning
through Saturday morning. Moisture convergence will persist
through the rest of the forecast cycle, helping sustain convection
across this region.

Another region of interest is west Ecuador and Peru. The period of
greatest precipitation impact will be Friday morning through
Saturday morning. During this period, mid - level winds are
expected to decrease, while the westerly low level flow will
continue to favor moisture convergence across the coast of
Ecuador. These conditions will favor a total precipitation maxima
of 40 - 80mm during this period. Starting Saturday evening, expect
an increase in upper level easterly winds, which will help sustain
diffluence and speed divergence across the region through Monday
morning. A total precipitation maxima of 30 - 60mm is possible
from Saturday morning through Sunday morning. By Sunday morning
through Monday morning, moisture convergence will prevail in the
region, however, an increase in mid level wind speeds will favor
an increase in shear, thus yielding to a relatively lower total
precipitation maxima for this period.

In northeast Brasil, a series of low level troughs accompanied
with moisture convergence will continue to impact this region
through the next three days. Note, upper level divergence and
diffleunce will become favorable for Saturday morning through
Sunday morning. From Friday morning through Sunday morning, a
daily total precipitation maxima of 30 - 60mm is possible.

Elsewhere in Tropical South America, the ITCZ, NET, and Southern
ITCZ will continue to favor diurnal convection. A series of low
level troughs will propagate across the region and will be
accompanied by moisture convergence, helping yield to higher total
precipitation maxima across the Amazon Basin. 

Morales...(WPC)