Why Our Next Big Solar Storm Warning Could Still Be a Guess

Eighteen months ago, a beautiful auroral display swept across the world, accompanying the first extreme geomagnetic storm in more than two decades. It was a landmark event not just for the spectacle but for what it revealed about our growing global dependence on reliable space-weather forecasting. When another storm drew headlines this month (November 2025), with an early “G5 watch” issued by forecasters, governments and operators activated contingency plans in anticipation of another major impact (the geomagnetic storm scale, G-scale, ranges from one to five, with five denoting the most extreme events). Yet the storm ultimately peaked at only G3, a level we expect hundreds of times in a solar cycle. That mismatch exposed a persistent weakness in how we observe and interpret the Sun.

The November events began with three coronal mass ejections (CMEs) erupting from the same active region over consecutive days. Using direct, head-on observations from the Sun–Earth line, scientists estimated their speeds and trajectories and issued a G4 storm watch for 12 November. When the first CME struck earlier than expected and with stronger parameters than the initial estimate, the risk escalated: successive CMEs often travel faster along the newly cleared path, and the potential for a combined impact grows. A G5 watch was released, triggering international preparedness actions. Power-grid operators revisited protection settings, communications providers reviewed continuity plans, and governments braced for potential disruption.

Then nothing happened, at least not at the predicted intensity or time. The CME did arrive, but just before midnight, and with a magnetic field that was only briefly and weakly aligned in the southward direction needed to strongly couple with Earth’s magnetic system. Without that sustained southward field, even an otherwise fast and dense CME cannot deliver a major geomagnetic storm. The result was a modest G3. This forecasting gap did not arise from poor judgement but from a fundamental observational void: after we watch a CME leave the Sun, we lose sight of its evolution for roughly 99% of the journey to Earth.

The limitations of this “single viewpoint” forecasting have been known for years. We can estimate initial CME speed, but we cannot track how it deforms, interacts with the solar wind or merges with other CMEs en route. Crucially, we cannot determine its magnetic structure, the key factor in storm severity, until the CME reaches the L1 point (Lagrange point 1), only about 30 minutes before Earth impact. Even this narrow window is presently fragile: the DSCOVR spacecraft, one of only two satellites providing L1 measurements, is offline, and ACE is approaching 30 years in space with ageing instruments.

Given the rising global reliance on vulnerable infrastructure: power networks, navigation systems, satellite constellations, living with this degree of uncertainty is no longer tenable. Forecasts that overshoot create costly false alarms; forecasts that undershoot risk real damage. The November mis-forecast was harmless, but it underscored how close we are to the limits of what current assets can deliver.

New capabilities are on the horizon, though they require sustained commitment. The NOAA–NASA SWFO-L1 mission is expected to restore robust solar-wind monitoring from mid-2026, stabilising the 30-minute warning baseline. Far more transformative would be the European Space Agency’s Vigil mission, planned for launch to the L5 Lagrange point in 2031. From that vantage point, Vigil would view CMEs from the side, enabling reliable speed and trajectory estimates and dramatically reducing arrival-time uncertainty. But its path to launch depends on political support through multiple rounds of ministerial scrutiny.

Beyond L5, deeper innovation is needed. A constellation of sensors placed in distant retrograde orbits (DRO) could offer early in-situ magnetic-field measurements, potentially hours, not minutes, before a CME reaches Earth. ESA’s planned demonstration of a DRO spacecraft in 2026, HENON, is a first step, but only that. These observational advances must be matched by improved modelling of CME structure, solar precursors and the complex interactions that determine whether an incoming CME will actually be geoeffective.

Accurate space-weather forecasting will always involve uncertainty, but it need not remain dominated by blind spots. The November storm was a reminder that our current system can predict the possibility of major events yet cannot confirm their true character until it is almost too late. If we want forecasts that are genuinely actionable, capable of guiding grid operators, satellite controllers and governments with confidence, then investment in new vantage points, new missions and new science is essential. Without it, our next “G5 watch” may leave us waiting once again, unsure whether a major storm is coming or whether the sky will stay quiet.