Tracking storms here and now
How forecasters at the Finnish Meteorological Institute put data from EUMETSAT programmes into action
On the weekend of 5–6 August 2023, while people in Finland were basking in a short stretch of hot weather, specialists at the Finnish Meteorological Institute (FMI) in Helsinki were bracing for a major storm.
Weather forecasts indicated a weather system, later named Storm Hans by meteorologists in Sweden, that could bring destructive winds and heavy rain to the Scandinavian peninsula. Some models even suggested it might be the largest convective storm – as it first looked like – to strike in a generation.
The FMI’s headquarters in Helsinki
Image: Courtesy of Sini Jääskeläinen
“When a storm like Hans first appears in the weather models, two feelings hit me at once: terror and excitement,” says Sini Jääskeläinen, an operational forecaster at the FMI, who worked eight consecutive days as Storm Hans approached Scandinavia.
Image: EUMETSAT
“We saw in the forecast models that hot, humid weather systems over southern and central Europe were on a collision course with cooler air masses over Scandinavia,” she explains. “These interactions of energy and humidity often create the perfect conditions for severe convective weather, as we’ve seen in previous events like Storm Sylvi, which struck Finland in August 2010, causing widespread damage.”
Storm tracking
When a major storm is predicted a week in advance, it triggers a chain of activity at the FMI’s forecast centre. Additional shifts are assigned, and meteorologists work around the clock to monitor the storm, coordinate with emergency services, and deliver media briefings.
“There’s a saying that a butterfly fluttering its wings in Peru can cause a sandstorm in the Sahara,” says Jääskeläinen. “When it comes to predicting storms, though, it’s not one butterfly we’re accounting for – it’s an immense number of dynamic factors.”
These factors, she explains, include temperature differences in the atmosphere, humidity levels, wind patterns, sea surface temperatures, cloud formations, and the shape of the land.
“With so many variables, it’s often impossible to predict the exact path of a storm and the possible convective features in a storm’s early stages. And with rare or complex systems, like Hans, this uncertainty can persist right up until the hours before it strikes.
“So, even without certainty about the storm’s trajectory, we had to prepare people as much as we could.”
Severe weather warnings were issued across Finland. People were urged to stay home, airport staff tethered loose equipment to the ground, and emergency services prepared for potential chaos.
“In Norway and Sweden, Hans forced the evacuation of thousands due to severe flooding, with some rivers reaching their highest levels in 50 years,” says Jääskeläinen.
Destruction of the dam in Braskereidfoss, Norway, following Storm Hans
“However, as the storm’s pressure front crossed the Gulf of Finland, its intensity subsided, leaving FMI forecasters with the difficult decision as to whether to downgrade the warnings.
“While the storm didn’t materialise as we initially feared in Finland, satellite and radar data still showed risks of high winds, heavy downpours, large hail, and localised flooding. Given the uncertainties, it was critical to keep the warnings in place. What caused significant disruption in Norway and Sweden could just as easily have impacted Finland.”
“Sandwich” visualisation produced using observations from Meteosat-12’s Flexible Combined Imager on 7 August 2023 at 08:00 UTC. This type of “sandwich” visualisation shows the difference in cloud temperatures: from red for colder parts to blue for warmer parts. It is particularly useful for observing and nowcasting storms and severe weather events as it clearly visualises varying cloud tops that can give information about the storm’s dynamics. On top of the storm in the bottom right corner of the FCI image, it is possible to make out at least three overshooting tops with colder (red) pixels.
Image: EUMETSAT
Towards better nowcasting
The social and economic impacts of severe weather across Europe have risen significantly over the past ten years, with studies indicating that severe storms are becoming both more frequent and more destructive.
“This is a trend expected to continue in the coming decades, driven by climate change – and one of the key challenges for forecasters is to minimise these uncertainties as much as possible,” says Jääskeläinen.
“Predicting the severity and impacts of extreme weather, such as convective thunderstorms, can be exceptionally challenging. One method forecasters use to tackle this is nowcasting – very short-term forecasts that combine numerical weather prediction models with direct observations of atmospheric conditions.
“Nowcasts are a vital last line of defence for protecting communities from the worst impacts of severe weather. Given the complexities involved, it’s crucial that we have as many tools as possible at our disposal to deliver these forecasts.”
Sini Jääskeläinen uses data from a wide range of sources to produce forecasts
Image: Courtesy of Sini Jääskeläinen
Tracking the development and movement of thunderstorms over Europe using MTG’s Lightning Imager. Every frame shows the accumulated flashes during the past two minutes. Larger and more persistent eastward-moving lightning clusters in the eastern and south-eastern parts of Europe represent mesoscale convective systems. More localised short-lived afternoon thunderstorms appear in Italy and over the Alps. On the last day shown in the animation, a high-latitude outbreak of thunderstorms moving eastward from Finland can be seen. This animation was made using three days’ worth of data, from midnight UTC on 22 June 2024 to 23:59 UTC 24 June 2024.
Video: EUMETSAT
The EUMETSAT-operated MTG-S satellite is scheduled to launch in summer 2025. This is an artistic impression of the Infrared Sounder (IRS) instrument, which will be able to provide information on horizontally, vertically, and temporally resolved water vapour and temperature structures of the atmosphere.
Video: EUMETSAT
These observations will soon be supplemented by data from the Meteosat Third Generation – Sounder 1 satellite, set for launch in summer 2025, which will deliver crucial observations relevant for identifying early convective changes in the atmosphere, such as sudden shifts in temperature and humidity.
“These data will address key gaps in direct atmospheric observations,” says Jääskeläinen, who has attended two specialist training courses aimed at maximising the use of EUMETSAT’s next-generation satellite data, organised by EUMETSAT and the European Severe Storms Laboratory.
“Before attending these courses, I think I underestimated the power of satellite data in forecasting. Now, it’s central to my work. It was incredible to see how accurately we could identify dangerous weather systems just from satellite imagery.
“Storm prediction isn’t something you learn in school – it comes from experience. That’s why training opportunities are one of the most valuable resources for forecasters to make the best use of new data.
“When dealing with something as challenging as storm forecasting, every new stream of data helps narrow down uncertainties.”
Sini Jääskeläinen has taken part in training courses aimed at enhancing forecasters’ skills in making use of data provided by next-generation satellite programmes
Image: Courtesy of Sini Jääskeläinen
Sini Jääskeläinen being interviewed by school children in Vietnam; producing a weather forecast specifically aimed at school children; and leading training courses for meteorologists in Rwanda and Tajikistan, as part of an FMI initiative to improve forecast skills around the world
Images: Courtesy of Sini Jääskeläinen
Capacity building
Jääskeläinen’s work at FMI extends beyond forecasting to teaching meteorology skills to a wide range of people, including professionals in organisations across Finland, young people, and meteorologists involved in FMI’s international projects in Asia and Africa.
“When I started secondary school, my granddad gave me a weather diary, and I filled it enthusiastically for nearly a decade,” she recalls. “With that record, I began looking for annual variations in weather patterns. Later, inspired by a teacher who explained how certain cloud types are clear signs that rain is to come, I fell in love with studying clouds. They’re fascinating because they tell a story about what’s likely to happen in the near future.”
One of the greatest joys of her role, Jääskeläinen says, is sharing this passion to inspire others, particularly in countries that can benefit substantially from more effective use and application of weather data.
“Weather affects everything – such as everyday life, event planning, and emergency services. In places with considerable gaps in resources and knowledge, closing those gaps can make a huge difference,” she says. “We teach meteorologists how to use sounding data, how to work with software tools, and how to recognise the main patterns driving weather and climate in their own regions.
“It’s not just about forecasting,” she adds. “You’re using maths, computing, physics, and communication skills to focus on solutions. You must make difficult decisions based on your expertise and advice from your colleagues. It’s a challenging but incredibly rewarding career.”
Author
Adam Gristwood
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