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FXSA20 KWBC 111917
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
317 PM EDT Tue Mar 11 2025

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

South America Forecast Bulletin 11 Mar 2025 at 1915 UTC:

Across the South American continent the general rainfall pattern
over the next 3 days will have significant rainfall coverage north
of latitude 15S. However, today and Wednesday, the combination of
a few factors  will cause showers and thunderstorms across
portions of Northern Argentina into Southern Bolivia today and
Wednesday but drying significantly for Thursday. South of latitude
35S, the general pattern will be dry with the exception of the
southernmost tip of Chile or a few showers are possible for the
next couple of days with minimal rainfall accumulation.

There is an upper trough with axis from east of the Falkland
Islands into North Central Argentina. Although the associated low
pressure will continue moving East, a portion of the trough will
become positively tilted and will have an axis that will extend
from around La Pampa and Buenos Aires into Cordoba  and Santa Fe
of Argentina on Wednesday. This trough will gradually deepen,
becoming a low pressure by Thursday night, with its center near
Uruguay and southeastern Brasil. There is also an upper ridge in
the Southeast Pacific that will move into southern Chile and
Argentina by Wednesday morning. By Thursday morning the ridge will
extend from the northern Patagonia to just east of the Falkland
Islands as it continues to move East. Meanwhile, a short weight
trough in the upper levels will move into Austral Chile and
Argentina late Wednesday into Thursday. Across Northern South
America there will be an upper high pressure entering northeast
Brasil and extending west into western Brasil today. That said,
most of northern South America, particularly Brasil, will be under
a high pressure in the upper levels. It is also worth mentioning
that there will be a nearly stationary low pressure in the east
Pacific near 28S/75W. Having a high pressure over Brasil and the
low across the eastern Pacific, as well as the deepening trough
over northeast Argentina will tighten the pressure gradient in the
upper levels across north to northeast Argentina, Uruguay and
southeast Brasil, producing an upper level jet which will support
thunderstorm potential.

The mid and upper levels are fairly vertically stacked, meaning
that the mid levels will also have a high pressure over Brasil,
which will provide some stability over most of the country.
However, areas in the periphery such as southern Bolivia to the
southeast into Uruguay and southeastern Brasil will have stronger
mid-level winds which will provide support for shower and
thunderstorm development.

As far as available moisture, across the northern half of South
America, that is north of Argentina Chile and Uruguay, the
precipitable water will be near to above normal, except for
portions of central to eastern Brasil from Mato Grosso to the east
as well as northeastern Brasil, which will have below normal
precipitable water today and Wednesday. Moisture will increase
across Mato Grosso on Thursday but most of the northeast quadrant
of Brasil will remain with near to below normal moisture on
Thursday. Southern South America, mainly Argentina, Chile and
Uruguay as well as the Rio Grande do Sul state of Brasil, will
observe mainly near to below normal moisture for the next 3 days.
That being said, there is a narrow band of moisture extending from
central Argentina into Uruguay today and Wednesday but it will dry
for Thursday. Another narrow band of moisture will move from south
of north through the Patagonia on Thursday.

In terms of rainfall accumulation amounts today, northern Brasil
as well as portions of southern Bolivia, Paraguay, and
southeastern Brasil can observe rainfall maxima up to 50mm, but
possibly higher across isolated portions of Bolivia and Paraguay.
Another section near Cordoba and Santa Fe of Argentina may receive
up to 50mm of rain. Other areas north of 20S can receive maximum
rainfall of up to 25 to 35mm. On Wednesday, there is a local
maximum of rain expected across southern Bolivia into northern
Paraguay where the daily maximum rainfall can reach 70mm, while
there is also a small section of coastal southeastern Brasil that
may receive up to 60mm. Elsewhere, north of 28S the daily rainfall
is expected to max out between 25 and 45mm, with northern Brasil
and northern Peru being on the higher end of the range.
Essentially, the vast majority of eastern Brasil, except for areas
along the east coast of Brasil, are expected to receive little to
no rain. Thursday is expected to be a little bit drier, with no
area in the continent being forecast over 45mm, although isolated
amounts over that are possible. That being said, most areas north
of 20S are expected to have daily rainfall Maxima between 25 and
45mm, with central to southern Peru into Bolivia and portions of
northwestern Brasil being on the higher end of the range. Most of
Eastern Brasil will observe little to no rain. Elsewhere, some
areas are expected to receive rain with maximum amounts somewhere
in the middle near 25 to 35mm. Most areas south of 35S are
expected to receive little to no rain over the next 3 days.



Alamo...(WPC)

$$