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FXSA20 KWBC 211935
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
235 PM EST Fri Feb 21 2025

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

South America Forecast Bulletin 21 Feb 2025 at 2000UTC:

In the upper levels...

The Bolivian High is expected to broaden across west - central
South America and extend into portions of far northwest Argentina
for the forecast cycle. The high will continue broadening and
begin losing its structure by Sunday morning. To the north, the
upper level easterly flow, associated with the Bolivian High, will
begin to also weaken after Sunday evening. Thereafter, with the
weakening of Bolivian High, expect a reduction of divergence and
diffluence across northwest Tropical South America. To the east, a
trough, with an axis across 29S 55W and 42S 50W on Friday
afternoon, will begin to develop a positive tilt through starting
Saturday morning and remain across southeast Brasil through the
rest of the forecast cycle.

In Mid - Latitude South America...

In Chile, a series of upper shortwave troughs will continue to
traverse south - central Chile through Monday morning. The period
of greatest precipitation impact will be from Friday through
Saturday morning and Sunday morning through Monday morning.
Favorable upper level dynamics conditions are anticipated,
favoring divergence in the region. In the lower levels, an
increase in low level wind speeds and an increase in moisture will
enhance moisture convergence and orographic effects across Austral
Chile. From Friday morning through Saturday morning, expect a
total precipitation maxima of 20 - 35mm with a risk for
thunderstorms. From Sunday morning through Monday morning, expect
a total precipitation maxima of 15 - 30mm.

In central Argentina, in the upper levels, the interaction between
the Bolivian High and upper trough across Brasil will enhance
upper divergence across east - central Argentina starting Saturday
morning through Monday morning. In the low levels, a broad high
pressure system will begin to develop off the Atlantic coast of
Argentina - Uruguay - South Brasil, helping drive a more south -
westerly low level flow across northeast Argentina. The increase
in moisture convergence, coupled with the upper dynamic pattern,
will yield to a total precipitation maxima of 20 - 40mm from
Saturday morning through Sunday morning with a slight risk for
severe weather. From Sunday morning through Monday morning, a
total precipitation maxima of 30 - 60mm is possible with a
marginal risk for severe weather.

In Tropical South America...

A region of interest is southeast Brasil, where the aforementioned
upper trough will help sustain a surface frontal system off the
southeast Atlantic coast of Brasil. As the frontal system moves
farther out to sea, low level winds will become more
northwesterly, increasing moisture convergence and orographic
effects across southeast Brasil. Expect a precipitation maxima of
20 - 35mm through Saturday morning. By Saturday evening, upper
level diffluence and an increase in moisture convergence across
southwest Brasil, southeast Bolivia, and northeast Paraguay will
yield to a total precipitation maxima of 20 - 45mm from Saturday
morning through Sunday morning.

Another region of interest is Bolivia. Through Saturday morning,
low level moisture convergence will persist across the region,
yielding to a total precipitation maxima of 20 - 35mm across west
- central Bolivia. By Sunday into Monday, the aforementioned upper
trough across southeast Brasil will enhance some speed divergence
into southern Bolivia. In the lower levels, expect some moisture
convergence, which may yield to a total precipitation maxima of 15
- 35mm from Sunday morning through Monday morning.

Elsewhere in Tropical South America, the ITCZ, NET, and Southern
ITCZ will continue to favor diurnal convection. A series of low
level troughs associated with moisture convergence will continue
to propagate across the region through the next three days. This
will favor higher maxima precipitation totals across north -
central Brasil, the Amazon Delta, and northeast Brasil. In west
Colombia and Ecuador, expect the low level wind flow to shift more
southwesterly after Friday evening and decreasing moisture
convergence across this region. The period of greatest
precipitation impact will be Saturday morning through Sunday
morning, when upper level speed divergence will be most favorable,
where a total precipitation maximum of 35 - 70mm is possible.
Thereafter, the upper level easterlies are expected to weaken.

In the west Amazon Basin, speed divergence will continue to
contribute to ascent in the region through Sunday evening. Daily
total precipitation maxima of 35 - 70mm are possible starting
Friday morning through Sunday morning. Some uncertainties on the
location of convection from Sunday morning through Monday morning
exists for the west Amazon Basin. However, the upper levels are
less favorable for divergence during this period. This may yield
to lower total precipitation maxima across the far west region of
the west Amazon Basin after Sunday morning.

Morales...(WPC)


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