Évora Researchers Sent 14 Weather Balloons Into Last Winter's Run of Seven Atmospheric Rivers, and Will Fly More This Winter
The storms that gave mainland Portugal its wettest February in 47 years were also a rare chance to measure Atlantic moisture high above the Alentejo. The data feeds the models behind weather forecasts.
Seven atmospheric rivers reached the Iberian Peninsula in less than a month between January and February this year, the Universidade de Évora (University of Évora) said on Sunday. Its researchers sent instrument balloons up through several of them, and they plan to do it again this winter.
Atmospheric rivers are long, narrow bands of water vapour that carry moisture from the tropical and subtropical Atlantic. When one meets a frontal system over land, it can bring days of heavy, persistent rain. "We had an exceptional sequence of atmospheric rivers in that period, with very significant consequences on the ground," Miguel Potes, director of the university's Centro de Investigação em Ciência e Tecnologia para o Sistema Terra e Energia (CREATE, the Earth Systems and Energy research centre), said in a statement sent to the news agency Lusa.
The wettest February in 47 years
The official record shows how unusual that winter was. The climate bulletin for February 2026 from the Instituto Português do Mar e da Atmosfera (IPMA, Portugal's weather and sea institute) found that 241.7 mm of rain fell on the mainland that month, more than three times the 1991 to 2020 average. That made it the wettest February in 47 years and the fifth wettest since records began in 1931. In much of the country rainfall reached three to four times the normal, and more than five times in Mora, Lavradio and Alvalade do Sado.
IPMA linked the worst of it, from 4 to 7 February during storms Leonardo and Marta, to low-pressure systems northwest of the peninsula. Their frontal systems carried large amounts of tropical and subtropical moisture, which the bulletin identifies as atmospheric rivers. Fronts from storms Nils and Oriana followed. By the end of the month, IPMA said, soils in the North, the interior Centre and parts of the upper Alentejo were saturated, and the hydrological year that began on 1 October 2025 was the wettest in 30 years.
In the Alentejo, CREATE's own stations recorded 252.8 mm in Portel, 243.8 mm in Évora and 252.1 mm at the university's Mitra campus, 12 kilometres from the city, all in February. The university said the episodes saturated soils, filled reservoirs and caused floods.
Balloons into the storm
The storms came during an international field campaign that studies the processes behind strong winds, heavy rain and dry-air intrusions over the North Atlantic and the Euro-Mediterranean region, and tests how well weather forecasting models represent them. Évora took part through EUROP, the European University RadiOsonde Partnership. Its team launched 14 radiosondes from CREATE's atmospheric sciences observatory in the city.
A radiosonde is a small instrument package lifted by a helium balloon. As it climbs, it measures temperature, humidity, pressure and wind. The aim, Potes said, was to see what was happening higher up, following the structure of the moisture and how it moved as each system passed.
Why it matters for forecasts
The university says the soundings also feed the numerical models that weather services use to forecast. Potes said that knowing an atmospheric river is on its way is not enough: forecasters also need to predict its path, how much moisture it carries and how that moisture will mix with other air to produce rain.
That matters for anyone deciding when to clear gutters, move a car out of a flood-prone street or postpone a trip. Last winter's run of storms, which began with Storm Kristin in late January, is still being paid for. In September, the European Commission proposed 261 million euros from the EU Solidarity Fund for Portugal, and farmers in 90 councils learned only at the end of that month what they would receive.
The CREATE team of researchers and doctoral students is preparing a new campaign for the coming winter. The university said it will launch more radiosondes as weather systems of interest pass over Évora.
