388 

FXUS20 KWBC 181938

PMDSA 



South America Forecast Discussion - International Desks

NWS Weather Prediction Center College Park MD

337 PM EDT Mon May 18 2026



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



Forecast Bulletin 18 May 2026 at 1930 UTC:



The next three days will feature a predominantly tropical

convective pattern across South America, while much of

extra-tropical South America remains comparatively dry aside from

periods of precipitation across southern Chile. Over the full

72-hour period through Wednesday night into Thursday morning, the

heaviest accumulated rainfall is expected across Colombia,

Ecuador, northern Peru, southern Venezuela, and portions of the

western Amazon Basin, where totals of 75-150 mm are forecast with

localized accumulations exceeding 200 mm, especially across

portions of central and western Colombia.



For today and tonight, a broad upper-level ridge remains

established across tropical South America, supporting widespread

convection in its periphery across Colombia, Ecuador, northern

Peru, and the western Amazon Basin. The heaviest rainfall is

expected across central and western Colombia, northeastern

Ecuador, and northern Peru, where daily totals of 30-60 mm are

expected with localized higher maxima in stronger thunderstorms.

Additional scattered convection will extend eastward across

southern Venezuela, the Guianas, and northern Brazil with totals

generally between 15-30 mm.



Farther south, most of subtropical and extra-tropical South

America remains under a relatively dry pattern. Limited

precipitation is expected across southeastern Brazil and Paraguay,

where isolated to scattered convection will generally produce less

than 15-30 mm. Across southern Chile and southern Patagonia, a

Pacific trough and associated frontal system will support light to

moderate precipitation, with snowfall likely across the higher

elevations of the southern Andes.



On Tuesday and Tuesday night, the tropical convective pattern

remains active across northern South America. The heaviest

precipitation continues to favor western Colombia, northwestern

Ecuador, and northern Peru, where persistent moisture convergence

and upslope flow along the Andes will support rainfall totals of

25-50 mm with locally higher amounts. Additional convection across

southern Venezuela, the Guianas, and the western Amazon Basin will

continue producing widespread totals between 15-45 mm.



Across subtropical South America, isolated convection persists

from southeastern Brazil, although rainfall amounts remain limited

with most areas receiving up to 15-30 mm. Farther south, southern

Chile remains the only portion of extra-tropical South America

experiencing organized precipitation as frontal systems move

through the far southern cone. Light to moderate rainfall and

mountain snowfall are possible across austral Chile and southern

Patagonia.



By Wednesday and Wednesday night, tropical South America continues

as the primary focus for convection. Widespread showers and

thunderstorms persist across Colombia, Ecuador, northern Peru,

Venezuela, and portions of northern Brazil, with daily totals

generally between 20-40 mm and isolated maxima above 60 mm,

especially near the eastern slopes of the Andes and across western

Colombia.



Meanwhile, much of central and southern Argentina, Uruguay, and

central Chile remain comparatively dry under stable conditions and

limited moisture availability. Across austral Chile and southern

Patagonia, little to no precipitation is forecast.



At upper levels, a broad ridge remains anchored across tropical

South America through the period, supporting persistent tropical

convection despite generally weak upper-level flow. In contrast,

the southern cone remains dominated by strong westerly flow and

embedded troughs south of the continent, although the strongest

dynamics and moisture remain displaced well to the south over the

Southern Ocean. As a result, the most active weather through

Wednesday night will remain concentrated across tropical South

America, while extra-tropical regions experience relatively

limited precipitation outside of southern Chile and Patagonia.



Alamo...(WPC)











$$