An unusual winter storm is bringing rain, thunderstorms, strong winds and mountain snow to northern Chile, including parts of the Atacama Desert, one of the driest environments on Earth.
REPORTES | El desierto de Atacama, en Chile, registró una rara nevada en zonas altas como el llano de Chajnantor y el Observatorio ALMA (a casi 3.000 metros de altitud), alcanzando temperaturas de -12°C y sensación térmica de -28°C.
— APRA ARAUCANíA 👍🏽🇨🇱 (@aprachile) August 17, 2026
Una tormenta invernal se acercó desde la zona… pic.twitter.com/ePEjkQWGWh
The episode is affecting areas from Arica y Parinacota and Tarapacá southward through Antofagasta, Atacama and northern Coquimbo on Tuesday, August 18.
Rainfall totals may appear small compared with storms elsewhere, but they are highly unusual for Chile’s hyper-arid northern coast. Dirección Meteorológica de Chile observations show measurable rainfall at stations where August precipitation is normally extremely limited.
The risk became reality at Puerto Viejo, in the coastal commune of Caldera, where heavy rain activated normally dry ravines and sent a flow of water, mud and debris downslope toward the settlement. Chile’s SENAPRED issued an emergency SAE evacuation message on August 17 for people near ravines and steep slopes after a mass-movement event was reported in the area. The episode illustrates why rainfall totals that would appear modest elsewhere can become dangerous in the Atacama: hard, sparsely vegetated ground promotes rapid runoff, while steep quebradas concentrate that water into fast-moving debris flows with little warning.
URGENTE – ATACAMA ⚠️ Se registra un aluvión en la localidad de Puerto Viejo, comuna de Caldera.
— Red Geocientífica de Chile (@RedGeoChile) August 17, 2026
©️ Video compartido por la comunidad de RedGeoChile. pic.twitter.com/vaYFmdycne
At Arica, annual rainfall has already reached 6.5 mm (0.26 in), compared with a normal accumulation of only around 1.8 mm (0.07 in) by this point in the year.
Cut-Off Low is the Main Driver Behind the Unusual Atacama Weather
The meteorological driver is a baja segregada, or cut-off low, moving across northern Chile.
A cut-off low forms when a pocket of cold air aloft becomes separated from the main upper-level circulation. In this case, the system has moved unusually far north, creating strong atmospheric instability over regions that normally experience extremely stable and dry conditions.
Cold air high in the atmosphere combined with comparatively warmer air below encourages stronger vertical motion and the development of showers and thunderstorms.
Increíble pero cierto 🤯
— Arica Es Bacán (@arica_es_bacan) August 18, 2026
Cae nieve en el pueblo de #Putre . Desde el año 2018 que no ocurría este fenómeno. ❄️#arica #aricayparinacota #aricaesbacán #chile #parati pic.twitter.com/magqBtDM7z
The same cut-off low is also producing unusually wintry conditions across higher parts of Atacama, with snow reaching elevations where it is far less common. The freezing level was forecast to fall to around 2,200 meters (7,200 feet), while mountain areas could receive up to 25 cm (9.8 in) of snow per day through Wednesday. The snowfall is another sign of the unusually cold air associated with the cut-off low, which has created a striking mix of weather across the region: rain and thunderstorms over the hyper-arid desert and coastal areas, mud and debris flows through normally dry ravines, and significant snowfall over the higher terrain.
Meteored forecasts highlighted an elevated risk of electrical storms and hail across Antofagasta and Atacama as the core of the cut-off low moved overhead on Tuesday. Mountain areas are cold enough for precipitation to fall as snow, while strong winds can create blowing snow at higher elevations.
Small Rainfall Totals, Can, In Fact, Cause Problems
In the Atacama, rainfall does not need to be extreme to become hazardous.
The desert’s exceptionally dry soils, steep terrain and normally dry channels, known locally as quebradas, can respond rapidly when concentrated rain falls over their catchments.
Water may run across hard desert surfaces rather than immediately soaking into the ground, concentrating runoff into channels and producing localized flash flooding or debris flows.
El paisaje del altiplano cambió por completo tras el paso de un sistema frontal que llevó humedad y precipitaciones a la Región de Antofagasta. Viviendas, caminos y montañas quedaron cubiertos por un extenso manto blanco.https://t.co/tsl1LaiieM pic.twitter.com/gqxooOGJnh
— debate.do (@midebate) August 18, 2026
Fresh Chilean reporting on Tuesday documented activated quebradas and road disruption across northern regions as authorities continued monitoring the system.
Conditions along the northern coast should gradually improve later Tuesday as the system moves through, although precipitation may persist over higher terrain into Wednesday morning.
