South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
137 PM EST Wed Feb 26 2025

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

South America Forecast Bulletin 26 Feb 2025 at 1845UTC:

In Mid - Latitude South America...

In central Argentina, in the upper levels, on Wednesday, upper
divergence will continue to be favorable across east - central
Argentina and Uruguay as an upper trough, located in east -
central Argentina on Wednesday morning, continues to move east,
exiting into the Atlantic by Wednesday evening. From Wednesday
evening through Friday morning, a shortwave upper trough will
traverse the region and will exit into the Atlantic by Friday
morning. Another upper trough will move across the region starting
Friday morning through Saturday morning. This upper level pattern
will help sustain the formation of low level troughs and surface
fronts in the region as well as enhancing upper divergence. In the
mid - levels, a series of shortwave troughs will also be
propagating through the region for the next three days.

A feature of interest from Wednesday into Thursday is a meandering
stationary front, located across Cordoba, Santa Fe, Entre Rios,
and Uruguay on Wednesday morning. Along and ahead of this front,
expect an increase in moisture convergence. The upper levels will
begin to support an increase in upper divergence across Cordoba
and Santa Fe by Wednesday afternoon. Moisture convergence will
also be favorable during this period, yielding to a total
precipitation maxima of 25 - 50mm. Also, pre-existing convection
associated with a shortwave upper trough across east - central
Argentina and Uruguay, will continue to favor higher precipitation
totals in this region through Wednesday evening. A total
precipitation maxima of 20 - 45mm with a marginal risk for severe
weather is possible across the north - east Argentina and Uruguay.

Starting Thursday, the South American Low Level Jet (SALLJ) will
dominate across the region through Saturday morning, increasing
moisture across central Argentina and Uruguay. The upper level
patterns will continue to favor upper divergence across the
region. Moisture convergence will still be favorable along and
ahead of the stationary front, yielding to a total precipitation
maxima of 30 - 60mm from Thursday morning through Friday morning,
and a total precipitation maxima of 35 - 70mm from Friday morning
through Saturday morning with slight risk for severe weather.

In Chile, a series of upper troughs and mid - level shortwave
troughs will continue to traverse central Chile through the next
three days. In the low levels, a feature of interest is an intense
long fetch moisture plume. It is expected to primarily affect
south - central Chile from Wednesday evening through mid-day
Friday. These conditions will yield a daily total precipitation
maxima of 15 - 25mm from Thursday morning through Saturday
morning. Another less intense moisture plume will begin to impact
north - austral Chile on Friday afternoon through Saturday
morning, yielding to a total precipitation maxima of 15mm.

In Tropical South America...

In Bolivia and Paraguay, a stationary upper trough, with an axis
at 22S 60W on Wednesday afternoon, will enhance speed divergence
across east Bolivia and Paraguay. However, this upper trough will
quickly weaken as a potent upper trough, with an axis at 18S 44W
on Wednesday afternoon, continues to broaden and retrograde west,
increasing subsidence across the region. Thus, the period of
greatest precipitation impact will be from Wednesday through
Thursday morning. In the low levels, an increase in northerly flow
will favor an increase in moisture across the region through
Thursday morning will favor a total precipitation maxima of 20 -
40mm during this period.

In northwest South America, through the forecast cycle, an
increase in low level westerlies and the effects of the ITCZ will
help sustain moisture convergence and favor orographic effects
across west Ecuador and Colombia. The period of greatest
precipitation impact will be Thursday morning through Friday
morning, when upper divergence will be most favorable, yielding to
a total precipitation maxima of 35 - 70mm during this period.
After Friday morning, an increase in moisture is possible for
Friday and Saturday, favoring a total precipitation maxima of 30 -
60mm in this region. In northwest Peru, the wind flow will shift
to a more northerly direction, which may help reduce moisture.

Another region of interest is northeast Brasil, where a series of
low level troughs, associated with moisture convergence, and the
ITCZ will continue to favor the development of convection. As the
aforementioned Brasilian upper trough retrogrades, an increase in
upper diffluence is possible in this region. These conditions in
northeast Brasil will yield a total precipitation maxima of 20 -
45mm through Thursday morning, a maxima of 20 - 35mm from Thursday
morning through Friday morning, and a maxima of 20 - 45mm from
Friday morning through Saturday morning.

Elsewhere in tropical South America, the ITCZ and NET will
continue to favor the diurnal convection. Low level troughs will
continue to propagate across the region and will be accompanied by
moisture convergence, helping yield to higher total precipitation
maxima.


Morales...(WPC)
Ledesma...(WPC)