South America Forecast Discussion - International Desks NWS Weather Prediction Center College Park MD 259 PM EST Mon Mar 03 2025 GFS data at ftpprd.ncep.noaa.gov/data/nccf/com/gfs/prod/ South America Forecast Bulletin 3 Mar 2025 at 2000UTC: In Mid - Latitude South America †In central Argentina, an upper trough, located across the central Chilean Andes on Monday afternoon, will begin to traverse central Argentina by Monday evening through Tuesday morning. During this period, expect an increase in upper divergence across this region. Thereafter, a series of shortwave upper and mid level troughs will move across the region and sustain upper divergence and vorticity advection, respectively, during their passage. This dynamic upper level regime will support meandering surface troughs. Another feature of interest is a vertically stacked high pressure system, which will continue to enhance northerly winds into central Argentina, where moisture convergence is expected along and ahead of a meandering surface trough. Note, precipitable water is above average and will help favor higher precipitation chances for the next three days. The period of greatest precipitation impact is Monday morning through Tuesday morning, where expect a total precipitation maxima of 30 - 60mm to be accompanied by a slight risk for severe weather. In Chile, starting Tuesday evening, an upper jet streak will begin to enter into austral Chile, increasing upper divergence across the region through Tuesday evening. During this same period, in the low levels, a strong occluded low pressure system will also help sustain strong 850 hPa wind speeds that are accompanied by a long fetch moisture plume. These conditions will favor moisture convergence and orographic effects across this region. This moisture plume will quickly move northward, and expect a significant decrease in 850 hPa wind speeds by Tuesday afternoon. Thus, the period of greatest precipitation impact will be Monday morning through Tuesday morning, where a total precipitation maxima of 20 - 35mm is possible in south austral Chile. Thereafter, another long fetch moisture plume will begin to impact central Chile starting Wednesday morning through Thursday morning, favoring a total precipitation maxima of 15 - 20mm across central Chile. In Tropical South America†An upper level trough, with an axis at 19S 57W on Monday afternoon, will begin to lose definition starting Tuesday afternoon. Another feature of interest is a broad upper ridge extending across west Bolivia and south Peru. These two features will continue to favor upper diffluence and speed divergence across central Bolivia. In the northern periphery of the upper ridge, easterly winds will continue to dominate through the forecast cycle, favoring upper diffluence and divergence in Ecuador and north Peru. In this region, in the lower levels, the wind flow direction will become more westerly after Tuesday afternoon, yielding to an increase in moisture convergence and orographic effects. Expect the greatest precipitation impact to be from Wednesday morning through Thursday morningwhere a a total precipitation maxima of 30 - 60mm is likely. Another region of interest is north - central Bolivia, where the upper level regime will favor divergence through the forecast cycle. In the lower levels, persistent moisture advection will favor an increase in moisture convergence and orographic effects across this region, where expect a daily total precipitation maxima of 20 - 35mm for the next three days. Elsewhere in tropical south america, the ITCZ and NET will continue to favor diurnal convection. Note, the ITCZ has become disorganized across the Pacific Basin. Elsewhere, a series of low level troughs will propagate across the region and will be accompanied by moisture convergence, helping yield to higher total precipitation maxima across the Amazon Basin. In northeast Brasil, the ITCZ and low level troughs will continue to favor higher total precipitation totals for the forecast cycle. Morales...(WPC)