034 FXUS20 KWBC 081917 PMDSA South America Forecast Discussion - International Desks NWS Weather Prediction Center College Park MD 316 PM EDT Wed Jul 08 2026 GFS data at ftpprd.ncep.noaa.gov/data/nccf/com/gfs/prod/ Forecast Bulletin 08 July 2026 at 1920 UTC: A series of frontal boundaries will be moving across austral and southern Chile for the next three days. The first frontal boundary is already moving across the region and is being accompanied by moderate total precipitation maxima. Across austral Chile, there will be a gradual decrease in precipitable water as an occluded front moves into the continent. Meanwhile, a weakening atmospheric river will be accompanying the cold front that will affect southern Chile for Wednesday. At the same time, a mid-level trough is moving overhead and is expected to move east of the Andes and into north-central Patagonia during the day on Wednesday. There will be vorticity advection with this system in Patagonia as well. As the frontal boundary moves across the Andes, it will re-project into Argentina. These conditions will favor broad low level circulation in the region that will support precipitation processes. Thus, expect enhanced total precipitation maxima across southern and austral Chile for Wednesday and the chance for rain and snow in Patagonia, where precipitation maxima will be moderate. On Thursday, another frontal boundary will be moving into the region. An upper jet streak max will also be present in the region that will support upper divergence. Expect precipitable water values to approach 30mm for this period. Thus, expect moderate to enhance total precipitation maxima on Thursday. On Friday, the frontal boundary and accompanying atmospheric river will be weakening, leading to a reduction in total precipitation maxima in the region. Another region of interest is southern Brasil and Paraguay for Thursday and Friday. Currently, there is uncertainty in the development of precipitation across the region. An upper level trough will be amplifying across the region starting on Thursday, which will support the decrease in surface pressure levels in the region. However, there is model inconsistency in the magnitude of the amplitude of the upper level trough. A more amplified upper level trough (ECMWF) will support the development of a weak frontal boundary in the region while a less amplitude solution (GFS) will support the development of a low level trough. Regardless, surface to low level cyclonic circulation will be present in the region for the end of the forecast cycle. Global models are also disagreeing on the moisture content in the region, with the ECMWF a more moist solution and thus higher totals. Overall, expect precipitation chances to increase for Thursday and Friday. Across the tropics, the propagation of tropical waves and low level troughs will continue to maintain daily showers and thunderstorms across the Guianas, Venezuela, and Colombia. Expect moderate total precipitation maxima in the vicinity of these features. Another region of interest is the Pacific coasts of Colombia and Ecuador. The presence of the Caribbean low level jet is helping support the increase of northerly low level winds into the Pacific, which will also be interacting with an enhanced southerly low level wind and leading to zones of low level convergence across Colombia for Wednesday and Thursday. At the same time, the passage of tropical waves across the Caribbean Sea will support the increase in low level cyclonic circulation across the Pacific. Meanwhile, the environment will remain moist for this period as well. Thus, expect enhanced total precipitation across Colombia and Ecuador for the next three days. Though, there will be a slight decrease in precipitation accumulations for Friday as the low level convergence and orographic effects decreaseacross Colombia. However, still expect prevailing and weak westerly low level winds with the development of a low level ridge off the Pacific coast of Ecuador. Tinoco-Morales...(WPC) $$