346
FXUS20 KWBC 271851
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
251 PM EDT Mon Apr 27 2026

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

Forecast Bulletin 27 April 2026 at 1845 UTC:

Over the next three days, the most significant rainfall across
South America is expected across southeastern Brazil, Colombia,
and the Amazonian regions of northern Peru, including the eastern
slopes of the Andes. Additional areas of enhanced precipitation
are expected across west-central Brazil, the Guianas, and portions
of northern Brazil, where totals may exceed 50 mm. Across the
southern half of Chile, liquid equivalent precipitation of 40 mm
or more is expected, particularly over the Andes, where much of
this will fall as snow.

A key feature through the period is a stationary front extending
from the southeast Atlantic into southeastern Brazil, then
westward along the Brazil-Paraguay border into Bolivia. This
boundary serves as a focus for low-level moisture convergence and
will support persistent rainfall across southeastern Brazil, with
totals locally reaching up to 60 mm and a risk of severe weather
on Tuesday into Wednesday.

Today into early Tuesday, the heaviest rainfall is expected across
northern Peru and northeastern Ecuador, where scattered showers
and thunderstorms will produce 20-40 mm, with locally higher
amounts. Across much of Brazil, convection remains more scattered,
with totals generally in the 15-30 mm range, as forcing remains
weak away from the frontal zone. Along the stationary front over
southeastern Brazil, convection begins to gradually organize late
in the period as moisture convergence increases and upper-level
support improves.

On Tuesday into Wednesday, the stationary front becomes more
active across southeastern Brazil. Persistent moisture convergence
along the boundary, combined with increasing upper-level
divergence, supports 30-60 mm, with localized higher amounts
possible. The risk of severe weather increases late Tuesday into
Wednesday, particularly near the Brazil-Paraguay border, where
instability and upper-level forcing overlap. Elsewhere, central
Brazil continues to see scattered convection with 20-35 mm, while
isolated maxima near 30-60 mm are possible across southwestern
Colombia.

Across southern Chile, a surge of Pacific moisture and strong
westerly flow supports widespread precipitation exceeding 40 mm
liquid equivalent, with snowfall across the Andes, especially in
terrain-favored areas.

Wednesday into Thursday, the stationary front remains in place
across southeastern Brazil, continuing to support rainfall totals
of 40 mm, with locally higher amounts possible. Convection may
become somewhat less organized later as upper-level support
weakens, but moisture convergence along the boundary sustains
rainfall through the period.

Across tropical South America, convection remains active but
generally scattered, with 20-30 mm and isolated maxima exceeding
40 mm, particularly along the eastern slopes of the Andes in Peru,
and across parts of western Colombia and Ecuador. Across southern
Chile, precipitation continues with 10-30 mm liquid equivalent,
and mountain snowfall persists due to continued upslope flow and
cold air in place.

Alamo...(WPC)



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