Imagine a storm that rumbles with thunder and intimidating lightning flashes, but not a single drop of rain falls. Dark clouds loom menacingly over a landscape already scorched by days of extreme heat, while lightning streaks across the sky without expected downpour.
This is not the script of a science fiction movie, but the reality of dry storms, one of the most dangerous and misunderstood weather phenomena of our time.
These events, which may seem harmless due to their lack of rain, are in fact one of the leading natural causes of forest fires worldwide.
Their deceptive nature hides a complex chain of atmospheric processes that, combined with increasingly frequent and intense heatwaves driven by climate change, are turning vast swathes of the planet into powder kegs waiting for a spark.
What are dry storms? The paradox of the electric sky
A dry storm is a meteorological phenomenon characterised by the presence of intense electrical activity accompanied by little or no precipitation actually reaching the ground.
This definition contains a fundamental paradox: the term “dry” describes only the outcome at the Earth’s surface, not the process occurring within the thunderstorm cloud.
From the perspective of atmospheric physics, all storms are initially “wet” phenomena. They are formed by the condensation of water vapour and generate precipitation within them, just like any conventional thunderstorm. The crucial difference lies in what happens to that rain as it descends to the ground.
In a dry storm, the precipitation that forms in the upper layers encounters, on its way down, a layer of extremely dry and warm air in the lower and middle levels. This “invisible barrier” causes raindrops or hail crystals to evaporate completely before they can reach the ground.
The most distinctive visual feature is the ‘virga’, filaments or curtains of precipitation that hang at the base of clouds but vanish into thin air before reaching the ground. This phenomenon, known colloquially as ghost rain, is visible evidence of a potentially very dangerous storm.
These storms are characterised by significant thunderstorms with intense lightning and thunder, little or no surface precipitation, the presence of virga, and violent wind gusts known as “blowdowns” that can exceed 100 km/h.
Heat waves are the perfect fuel for dry storms
The relationship between dry storms and heat waves is not simply a meteorological coincidence, but a dangerous synergy that creates the perfect conditions for large-scale natural disasters.
Heat waves act as a catalyst on two fundamental fronts. On the one hand, they perform atmospheric preparation: the intense and persistent heat creates strong instability in the lower layers of the atmosphere, generating powerful updrafts that feed the formation of storm clouds. At the same time, high temperatures create that distinctive vertical structure with very warm air at the surface and a layer of dry air at mid-levels – the perfect recipe for rain to evaporate before reaching the ground.
They also transform the landscape in a potentially lethal way. Days or weeks of extreme heat and low humidity dehydrate vegetation, dry out the soil and reduce the moisture content of forest fuels to critically low levels. This process transforms the territory into a veritable “powder keg” that needs only a spark to ignite.
The interaction between these phenomena can create particularly dangerous vicious circles. Unlike wet storms, which provide thermal relief with their rain and cold currents, dry storms do not interrupt the heat pressure.
In extreme cases, they can trigger “heat bursts” or powerful downdrafts that warm rapidly due to compression, leading to sudden temperature spikes of over 10°C within minutes, often accompanied by hurricane-force winds.
Global warming is intensifying this dangerous synergy. A warmer atmosphere holds more water vapour, intensifying the entire hydrological cycle. This results in more intense rainfall in some regions, but also in more rapid evaporation. In aridity-prone areas such as the Mediterranean, this leads to more severe droughts and more flammable landscapes.
Modelling indicates that climate change will make heat waves become more frequent, intense and longer-lasting, creating the ideal conditions for dry storms to become the new summer normal.
The many dangers of a seemingly harmless dry storm
The lack of rainfall in dry storms can create a deceptive sense of safety, one that can prove deadly. Beneath their seemingly harmless appearance lies a chain reaction of interconnected dangers far more serious than they appear.
The most direct and devastating hazard is dry lightning, cloud-to-ground lightning strikes that occur without the natural protection of rain. Lightning can heat the surrounding air up to 30,000°C, and when it strikes vegetation previously dried out by heat, ignition is almost instantaneous.
In a wet storm, subsequent rain often extinguishes these small outbreaks before they spread. In a dry storm, the fire is free to establish and grow. Smouldering fires may also burn slowly for hours or days with no visible flame, only to break out suddenly when weather conditions change.
Dry storms can also produce blowdowns, intense downdrafts capable of generating straight-line winds exceeding 120 km/h. Dry blowdowns occur when air cools due to the evaporation of virga, while warm blowdowns result from air masses heating up through compression as they descend.
These powerful winds can topple trees, damage infrastructure, and, in wildfire conditions, act like massive bellows, rapidly fanning the flames and triggering explosive fire spread.
The third major risk is severe deterioration of air quality. Powerful winds can stir up enormous amounts of dust and sand, creating dust storms that reduce visibility to zero and carry particles hazardous to the respiratory system. Fires started by dry lightning also generate smoke laden with particularly dangerous fine particles, capable of entering the bloodstream.
This smoke can travel hundreds of kilometres, affecting air quality in cities far away from the original fire.
The true danger lies in how these threats are interconnected: lightning ignites the fire, powerful blowdown winds escalate it into a firestorm, and together they unleash an air quality crisis that can linger for weeks and impact millions of people.
Spain experienced a clear example of this phenomenon in 1979, in the Ayora-Enguera region (Valencia). During an intense heatwave, a fire sparked by dry lightning tore through approximately 44,000 hectares. This event remains a historic illustration of the destructive chain reaction that climate change is increasingly turning into a new reality for vulnerable areas like the Mediterranean.