South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
221 PM EST Tue Mar 04 2025

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

South America Forecast Bulletin 4 Mar 2025 at 1930UTC:

In Mid - Latitude South America...

In Central Argentina, starting Tuesday evening through Thursday
morning, two shortwave upper troughs will traverse the region,
favoring upper divergence and diffluence. During this time, a
series of shortwave troughs and a surface stationary front will
help trigger convection across this region. At the 850 hPa level,
the South American Low Level Jet (SALLJ) will continue to
strengthen, helping drive moisture into central Argentina through
the next three days. Ahead and along this front, the subtle
increase in moisture will enhance moisture convergence in the
region. These conditions will favor a total precipitation maxima
of 20 - 40mm from Tuesday morning through Wednesday morning, and a
total precipitation maxima of 25 - 50mm from Wednesday morning
through Thursday morning. Severe weather risks exist during this
period. After Thursday evening, a potent upper trough will begin
to propagate across the Chilean Andes and exit into the Atlantic
Basin by Saturday afternoon. During this period, expect an
increase in divergence during its passage. Frontogenesis is also
anticipated across central Argentina, which will help in the
initiation of precipitation. Moisture convergence will be most
favorable ahead and along the cold front, yielding to a total
precipitation maxima of 30 - 60mm from Thursday morning through
Friday morning with a slight risk for severe weather.

In Chile, from Tuesday morning through Thursday morning, a series
of upper jet streaks will continue to favor upper divergence
across central Chile. The period of greatest precipitation impact
is Wednesday morning through Thursday morning, when a total
precipitation maxima of 20 - 40mm is possible. During this period,
expect a jet streak to move across central Chile ahead of the
passage of a potent upper trough on Thursday, which will yield to
an increase in upper divergence. At the lower levels, a long fetch
moisture plume, accompanied by strong wind speeds, will begin to
impact central Chile by Wednesday morning through Thursday
afternoon, yielding to an increase in moisture convergence and
orographic effects.

In Tropical South America...

In Bolivia, the Bolivian High appears to be developing across
northwest Bolivia and south Peru, where its axis is estimated to
be located at 15S 70W on Tuesday afternoon. It is anticipated to
strengthen towards the end of the forecast cycle. This ridge will
be interacting with a weakening upper trough, with an axis at 18S
57W on Tuesday afternoon, through the next three days. Across
south - east Bolivia, expect speed divergence and diffluence to be
most favorable from Tuesday morning through Wednesday morning.
Thereafter, the upper level flow speed will decrease, but,
divergence will continue being favorable across this region for
the remainder of the forecast cycle. At the lower levels, a
stationary low level trough will remain across central Bolivia,
helping enhance moisture convergence. The greatest precipitation
impact will be from Tuesday morning through Wednesday morning,
where a total precipitation maxima of 30 - 60mm is likely in this
region. From Wednesday morning through Friday morning, expect a
daily total precipitation maxima of 20 - 40mm.

In Ecuador and Bolivia, upper level easterlies will dominate for
the next three days, enhancing upper divergence and diffluence. At
the mid - levels, weak wind speeds will persist through Wednesday
evening and increase after, stimulating an increase of shear after
Wednesday. At the low levels, the wind direction will be mostly
from the west and north through Tuesday afternoon. This will favor
moisture convergence and orographic effects. Thus, these
conditions will yield to a daily total precipitation maxima of 25
- 50mm from Tuesday morning through Thursday morning. After
Wednesday, daily total precipitation maxima will decrease slightly
in Ecuador.

Elsewhere in Tropical South America, diurnal convection will
remain favorable along the ITCZ and NET through the next three
days. Also, a series of low level troughs, accompanied by moisture
convergence, will continue to traverse north Brasil and the Amazon
Basin, yielding to higher daily precipitation maxima. In northeast
Brasil, along the Amazon Delta, expect the period of greatest
precipitation impact from Tuesday morning through Wednesday
morning, when the mid level winds will be weakest. A total
precipitation maxima of 25 - 50mm is possible during this period.



Tinoco - Morales...(WPC)