South America Forecast Discussion - International Desks NWS Weather Prediction Center College Park MD 223 PM EDT Wed Mar 12 2025 GFS data at ftpprd.ncep.noaa.gov/data/nccf/com/gfs/prod/ SOUTH AMERICAN FORECAST BULLETIN 12 March 2025 AT 14:00 UTC ...Climate/Teleconnections Conditions... MJO: The MJO is currently in phase 2. The enhanced convective phase is currently crossing Africa and entering the Indian Ocean Basin. ENSO conditions: La Nina conditions are present, a transition to ENSO neutral is expected from April to May. ...Synoptic conditions over tropical South America... A region of particular interest is Ecuador and the far southwest of Colombia, where warm sea surface temperatures (SSTs), the Pacific Intertropical Convergence Zone (ITCZ) and weak onshore flow at the lower levels along the Pacific ITCZ will likely enhance the sea breeze development, which helps transport moisture inland during the day on Thursday and Friday, to continue driving isolated diurnal convection. This increased moisture supply further supports convective activity over Ecuador and southwest Colombia, contributing to sustained atmospheric instability and cloud formation in the region. This convection is further supported by upper-level divergence, which facilitates the upward motion of air, creating favorable conditions for the development of convective clouds. The transport of moisture by trade winds around the Intertropical Convergence Zone (ITCZ) into the central region of tropical South America, combined with upper-level divergence, plays a critical role in enhancing precipitation along the northern extension of the NET/ITCZ. The trade winds carry warm, moist air from the ocean surface toward the ITCZ, where it converges, rises, and cools, leading to condensation and cloud formation. Upper-level divergence further supports this process by creating a favorable environment for upward motion. This dynamic interaction between moisture transport, lower level convergence, and upper-level divergence will continue sustaining precipitation along the NET/ ITCZ, impacting northwestern Brasil, as well as the southern parts of Venezuela Colombia. The upper-level divergence, combined with the trade winds as they approach the northern coast of South America, from Guyana to northeastern Brasil, will facilitate convergence along the coast. This instability is likely to lead to the formation of convective clouds. Furthermore, the interaction with the sea breeze may enhance the development of these convective clouds during the next 3 days. These systems can spread widely and move inland into the continent. ...Synoptic conditions for Brasil†A persistent and expansive surface high-pressure system centered at Pantanal and Mato Grosso in Brasil will promote moist easterly to, northeasterly winds, that will result in a narrow coastal band of cloud cover around the periphery of the high pressure in the northwestern region of Brasil during the evening throughout the upcoming forecast cycle. ...Synoptic conditions for Bolivia, Paraguay, Uruguay and Argentina... In the upper levels, there is a trough with its axis just east of southern South America, its base being over central Argentina propagating slightly to the north and exiting South America from today (Wednesday) into Thursday morning. In the mid levels, the overall patterns are forecast to be similar to the upper levels, meaning that the troughs and ridges, as well as the high pressure over northern South America are fairly vertically stacked. This pattern will also provide a mid-level jet in the southern periphery of the high pressure, which will provide ventilation along a low-level trough, enhancing shower and thunderstorm potential from southern Bolivia through Paraguay and into southeast Brasil, mainly today (Wednesday) into early Thursday. Easterly winds at the mid and upper levels will enhance moisture influx from the interior of the continent near the Altiplano surface. The upper and mid-level trough will also be a contributor to the enhanced shower and thunderstorm potential over northern Argentina into Uruguay and extreme southeast Brasil. A stationary front over the region northern Argentina and southern Brasil is expected to dissipate by tonight (Wednesday night) . Showers and thunderstorms are expected to develop along the frontal boundary, mainly affecting northwest Argentina and Paraguay (the Chaco region) this afternoon and drying out by Thursday. The northern region of Uruguay and southeastern Brazil will also experience elevated temperatures on Wednesday along the coast due to the development of a frontal boundary to the east. Additionally, local effects, such as sea breezes, will enhance the likelihood of showers and thunderstorms on that day. After that, drier conditions and a more stable atmosphere is expected in those regions from Thursday into Friday As the strong surface high pressure system advances from Thursday evening into Friday, dry and stable conditions will prevail over Argentina, Uruguay, and Paraguay. ...Synoptic conditions for Chile... As the high-pressure system advances toward Chile and Argentina, predominantly stable conditions are expected over the Norte Grande and Norte Chico regions, as well as the central zone from today (Wednesday) into Friday. The stable conditions in the northern and central zones are associated with subsidence induced by the high-pressure system, which suppresses vertical motion and limits cloud development. In the southern and austral regions, conditions will also remain mostly stable, with the development of stratiform clouds. An upper level jet will move into Zona Austral from today (Wednesday) into Thursday morning and it will support the development of stratiform rain, although low-level moisture advection is expected to be limited. For more QPF graphical information: https://www.wpc.ncep.noaa.gov/international/sam_day1-3.shtml Ledesma...(WPC) Alamo...(WPC)