Dry lightning is absolutely real, and it is one of the most dangerous weather phenomena for wildfire ignition. The term refers to lightning strikes that reach the ground while producing little or no measurable rainfall, typically defined by meteorologists as less than 2.5 millimeters of rain at the surface.1Environmental Research: Climate. Meteorological and geographical factors associated with dry lightning in central and northern California It forms the same way any thunderstorm lightning forms, through charge separation inside towering clouds, but the rain that falls never makes it to the ground. The result is a bolt of electricity striking bone-dry terrain with no accompanying moisture to dampen the fire risk.
What Makes Lightning “Dry”
All lightning requires the same basic ingredients: moisture rising into the atmosphere, unstable air that lets clouds build vertically, and ice particles colliding inside the cloud to generate electrical charge. In a typical thunderstorm, the rain that forms in the cloud reaches the ground and wets the surface, making it harder for a lightning strike to start a fire. Dry lightning happens when the atmosphere below the cloud base is so warm and dry that the falling rain evaporates before it ever touches the ground. Meteorologists call this evaporating rain “virga,” and you can sometimes see it as a hazy curtain hanging beneath a cloud that never reaches the earth.
This setup is most common in regions with high cloud bases, meaning the bottom of the thunderstorm sits far above the ground. The western United States, parts of Australia, central Brazil, and other semiarid landscapes are particularly prone because their low surface humidity and high temperatures create a deep layer of dry air between the cloud and the terrain. A thunderstorm can be dumping rain at 20,000 feet, generating plenty of electrical activity, while the ground below remains parched.
In central Brazil, researchers examining lightning-caused wildfires found that when cloud-to-ground lightning was matched to actual fire starts, the average precipitation at the surface was less than 1 millimeter, compared to about 6 millimeters for general cloud-to-ground lightning in the same region. Relative humidity near the fires averaged around 48 percent versus 57 percent for lightning events that did not cause fires.1Environmental Research: Climate. Meteorological and geographical factors associated with dry lightning in central and northern California The pattern is consistent: the drier the air below the storm, the greater the chance that a strike will land on fuel ready to burn.
Why Dry Lightning Is So Effective at Starting Fires
Not every lightning strike is equally good at igniting vegetation. Researchers have identified a particular type of electrical discharge called a “continuing current” that is especially dangerous. Most lightning is a rapid pulse lasting only a fraction of a second, but continuing-current flashes sustain their electrical flow for tens to hundreds of milliseconds after the initial stroke. That prolonged contact with the ground deposits far more energy into whatever it hits, making ignition much more likely.
A study examining thousands of lightning-ignited fires in North America found that the probability of a fire starting was significantly higher when the lightning flash carried a continuing current lasting more than 10 milliseconds. The researchers even documented one fire-igniting flash with a continuing current lasting roughly 400 milliseconds, associated with a visible optical signal that persisted for two to four seconds.2Journal of Geophysical Research: Atmospheres. On the Role of Continuing Currents in Lightning‐Induced Fire Ignition That is a remarkably long time for electrical energy to be pouring into a single point on the ground.
A separate large-scale analysis of nearly 5,900 lightning-ignited wildfires found that continuing-current flashes make up less than 10 percent of all lightning in North American summers, yet they are responsible for a disproportionate share of fire starts. The probability of ignition from a continuing-current flash is considerably higher than from ordinary cloud-to-ground lightning without that sustained flow.3PubMed Central. Variation of lightning-ignited wildfire patterns under climate change When this kind of flash lands in a dry-lightning scenario, where there is no rain to wet the fuel, the combination is extremely effective at starting fires.
Holdover Fires and Delayed Detection
One of the sneakier aspects of dry lightning fires is that they do not always flare up immediately. A lightning strike can smolder in duff, roots, or deep organic soil for days before producing visible flames or smoke. These are called “holdover fires,” and they pose a real problem for fire managers because the eventual fire can appear far removed in time from the lightning event that caused it.
Research on lightning-ignited wildfires in the western United States found that holdover fires, detected two to five days after the igniting strike, actually occurred with higher precipitation at the time of the strike, averaging about 5.1 millimeters, compared to about 2.5 millimeters for fires detected promptly.4Geophysical Research Letters. Lightning‐Ignited Wildfires in the Western United States: Ignition Precipitation and Associated Environmental Conditions That sounds counterintuitive until you think about it: a strike that occurs during a wetter storm may only smolder underground, suppressed by the rain, then emerge days later when conditions dry out. The initial moisture delays the fire rather than preventing it. This means even a thunderstorm that technically delivers some rain can set a time bomb in the landscape.
For fire lookouts and satellite monitoring systems, holdover fires are a headache because they can pop up in remote areas with no obvious connection to recent weather. By the time the fire is spotted, the lightning event that started it may be old news, and the fire has had days to establish itself in difficult terrain.
The 2008 California Lightning Siege
One of the most dramatic examples of dry lightning’s destructive potential occurred on June 20 and 21, 2008, across central and northern California. An unusual weather pattern brought widespread thunderstorms to the region, but the storms produced frequent lightning with almost no rain reaching the ground. More than 1,500 new fires ignited in just two days.5Weather and Forecasting. Using the 21 June 2008 California Lightning Outbreak to Improve Dry Lightning Forecast Procedures Many of those fires grew large, and firefighting efforts stretched into August before all of them were contained.
The event overwhelmed California’s fire suppression resources and became a case study in why dry lightning forecasting matters. Afterward, researchers used the outbreak to refine their prediction tools, looking at what atmospheric conditions preceded the event and how forecasters might identify similar setups earlier. The 2008 siege remains one of the clearest illustrations of how a single dry-lightning event can reshape an entire fire season.
When Fire Creates Its Own Lightning
In a strange feedback loop, large wildfires can generate their own thunderstorms, which then produce additional lightning that can start new fires. These fire-generated storms, called pyrocumulonimbus clouds, form when a high-intensity wildfire generates enough heat and smoke to punch a convective column into the upper atmosphere. The column behaves like a conventional thunderstorm, producing hail, powerful downdraft winds, and even tornadoes, but with one critical difference: it does not typically produce significant rain.6Communications Earth & Environment. Understanding the critical elements of the pyrocumulonimbus storm sparked by high-intensity wildland fire
This means a pyrocumulonimbus cloud can loft lightning bolts onto the landscape while the fire below rages on and the air stays dry. In some cases, the storm’s downdraft winds scatter burning embers over a wide area, creating spot fires kilometers ahead of the main fire front. The fire is, in effect, manufacturing its own dry-lightning engine. These events have been documented with increasing frequency, and some researchers consider them among the most extreme fire-weather phenomena on Earth. The smoke plume from a pyrocumulonimbus can reach the lower stratosphere, injecting aerosols that linger for months.
Detecting Dry Lightning Events
Identifying dry lightning as it happens is essential for getting firefighters in position before small ignitions become large fires. Two main tools handle this. Ground-based networks like the U.S. National Lightning Detection Network (NLDN) detect the electromagnetic pulse from each lightning stroke and geolocate it. These have been operational for decades and provide reliable coverage across much of North America. In recent years, satellite-based instruments like the Geostationary Lightning Mapper (GLM) on the GOES-16 and GOES-17 satellites have added another layer of observation, detecting lightning from orbit by sensing the brief optical flash it produces at the cloud top.7Journal of Geophysical Research: Atmospheres. Comparisons of Lightning Rates and Properties From the U.S. National Lightning Detection Network (NLDN) and GLD360 With GOES‐16 Geostationary Lightning Mapper and Advanced Baseline Imager Data
Nighttime visible satellite imagery offers yet another method: automated algorithms can scan satellite data for lightning flashes and cross-reference them with ground networks. Comparisons between satellite-based detection and the NLDN show general consistency within the expected detection limits of each system.8Weather and Forecasting. Automated Lightning Flash Detection in Nighttime Visible Satellite Data The challenge is not just detecting the lightning but pairing it with real-time precipitation data to determine whether a given strike was “dry.” Radar can estimate rain reaching the ground, but in remote or mountainous terrain, radar coverage has gaps. Combining lightning detection with surface weather stations, radar, and satellite precipitation estimates gives the most complete picture, but it remains imperfect, especially in the vast wilderness areas where dry lightning fires are most common and least accessible.
Climate Change and the Growing Risk
Multiple lines of evidence suggest that dry lightning will become more frequent as the climate warms. Warmer air holds more moisture, which fuels more vigorous thunderstorm convection. At the same time, hotter surface temperatures in semiarid regions mean the air below storm clouds becomes even more effective at evaporating falling rain, widening the gap between the cloud producing precipitation and any moisture reaching the ground.
Climate projections for the western United States point to widespread increases in the number of days per year with cloud-to-ground lightning by mid-century. Under a moderate warming scenario, many areas in the northern part of the region could experience four to twelve additional lightning days per year compared to the period from 1995 to 2022, driven by increases in the atmospheric variables that power thunderstorms.9Earth’s Future. Projections of Lightning‐Ignited Wildfire Risk in the Western United States More lightning days over drying landscapes means more chances for dry strikes.
Global analyses tell a similar story. Machine learning models trained on satellite-observed fire and lightning data show that even over a relatively short span of less than a decade, climate changes have already measurably increased the global risk of lightning-ignited wildfires.10PubMed Central. Global lightning-ignited wildfires prediction and climate change projections based on explainable machine learning models The trend is not uniform; some tropical regions see shifts in ignition patterns that differ from those in boreal or temperate zones. But the overall direction is clear: a warmer planet favors more lightning, drier fuels, and a larger window of time each year during which fires can take hold.
This has implications beyond just counting fires. Lightning-ignited wildfires tend to burn in remote, rugged terrain where suppression is expensive and difficult. They also contribute to the feedback loop of pyrocumulonimbus events described earlier, meaning that more dry lightning can feed a cycle of more extreme fire behavior, more smoke, and more stratospheric aerosol injection.
How Dry Lightning Differs From Volcanic and Dust-Storm Lightning
Dry lightning from thunderstorms is not the only form of lightning that occurs without significant rainfall. Volcanic eruptions produce their own lightning, and the mechanisms are distinct from what happens inside a rain cloud. In a volcanic plume, electrical charge builds through several processes: particles fracturing during the explosion itself, ash grains rubbing against one another as they are swept upward, interactions between ash and water or ice, and even natural radioactivity from the erupted material.11Journal of Volcanology and Geothermal Research. A review of volcanic electrification of the atmosphere and volcanic lightning The result is spectacular lightning within the eruption column and ash cloud, entirely independent of conventional rain-bearing weather.
Laboratory experiments on volcanic ash have confirmed that the size distribution of the particles plays a key role in how much electrical charge is generated. Wider spreads of particle sizes lead to more vigorous charging, because large and small grains exchange charge differently when they collide.12PubMed. Triboelectric charging of volcanic ash from the 2011 Grímsvötn eruption This is fundamentally different from ice-crystal collisions inside a thundercloud, though the end result, a massive electrical discharge through the air, looks similar from the outside.
Dust storms can also produce electrical discharges, though rarely at the scale of volcanic or thunderstorm lightning. On Earth, dust devils and sandstorms generate charge through friction between sand and dust particles. On Mars, the same process is expected to be more intense. Martian dust devils and dust storms are larger, stronger, and more frequent than those on Earth, and the thin Martian atmosphere means electrical breakdown happens at a much lower voltage threshold.13Geophysical Research Letters. Electrical discharges and broadband radio emission by Martian dust devils and dust storms If future missions to Mars carry the right instruments, we may eventually detect Martian “dry lightning” generated entirely by windblown dust, with no clouds or precipitation involved at all.
Common Misconceptions About Dry Lightning
The most persistent misunderstanding is that dry lightning is somehow a different kind of lightning, a unique electrical phenomenon. It is not. The lightning itself is physically identical to any other cloud-to-ground strike. The “dry” part describes the surface conditions, not the bolt. A storm producing dry lightning may look unremarkable on radar at cloud level; it is only at the ground that the absence of rain makes the event dangerous.
Another misconception is that dry lightning only matters in the American West. While California and the interior West get the most attention because of their fire seasons, dry lightning ignites fires across every continent with vegetation. Central Brazil, the Mediterranean, boreal forests in Canada and Russia, and parts of Australia all experience significant dry-lightning fire seasons. The conditions needed, high cloud bases, unstable air, and dry surface fuels, are not limited to any single geography.
People also tend to underestimate how far a fire start can be from the storm that caused it. A thunderstorm cell producing dry lightning can be compact and fast-moving. By the time anyone investigates the ignition, the storm may have moved on or dissipated entirely. Combine that with holdover fires smoldering for days before breaking out, and the connection between a specific lightning event and a specific wildfire can be genuinely hard to trace. This is part of why accurate lightning detection networks and careful post-fire investigation matter so much: without them, many dry-lightning ignitions would be chalked up to unknown causes.
Finally, there is a tendency to think of dry lightning as rare. In absolute terms, most lightning around the world does arrive with some rainfall, so dry lightning is the minority case. But in fire-prone regions during peak fire season, it is remarkably common and accounts for a substantial share of wildfire ignitions. In central and northern California, dry lightning is considered a major source of wildfire starts, and individual events can produce hundreds or thousands of fires in a single outbreak.1Environmental Research: Climate. Meteorological and geographical factors associated with dry lightning in central and northern California Rare in everyday experience, perhaps, but when it shows up, it shows up at scale.