Solar Cycle Twenty-Five, the May Two Thousand Twenty-Four G-Five Geomagnetic Storm, and What Space Weather Actually Costs When You're Flying WAAS Approaches to Minimums

In May 2024, a series of extreme solar events caused widespread WAAS GPS degradation across North America and Europe, downgrading active LPV approaches to LNAV minimums with little warning. The culprit was a G-5 geomagnetic storm - the highest category on the geomagnetic storm scale - driven by Solar Cycle Twenty-Five, which has tracked significantly above its predicted intensity. This is not a theoretical risk. It is an operational reality that IFR pilots flying glass cockpits need to plan for right now.

What Happened During the May 2024 Geomagnetic Storm

Beginning around May 10, 2024, the sun produced a series of X-class solar flares - the strongest intensity category in the flare classification system - from a sunspot region designated AR 3564. Those flares were followed by coronal mass ejections (CMEs): massive bubbles of magnetized plasma launched from the solar surface at speeds between 1,000 and 3,000 kilometers per second.

When those CMEs reached Earth, they interacted with the planet’s magnetic field. That interaction is a geomagnetic storm. Scientists measure intensity using the Kp index, a scale from zero to nine. The May 2024 events reached Kp 9 - a G-5, the maximum category.

The last G-5 storm before this was October 2003, the Halloween storms. That event knocked out power transformers in South Africa, disrupted communications aboard the International Space Station, forced airline polar route reroutes, and caused GPS receivers worldwide to report unexplained position errors. The May 2024 storm matched that intensity - during a period when general aviation is more GPS-dependent than at any point in history.

Notably, the CME arrived at Earth several hours earlier than NOAA’s Space Weather Prediction Center forecast. That is not a criticism of the scientists - it is a data point about the state of the science. Space weather forecasting is roughly where terrestrial weather forecasting was in the 1960s. We know the storms exist and are coming. Precise, go/no-go timing predictions remain out of reach.

Why Solar Storms Disrupt GPS

GPS signals do not travel through vacuum all the way to your antenna. They pass through the ionosphere - a layer of the upper atmosphere sitting roughly 40 to 600 miles above the surface that is ionized by solar radiation.

Under normal conditions, the ionosphere causes small, predictable delays in GPS signal propagation. The GPS system accounts for those delays using mathematical models, and your receiver gives you an accurate position. During a geomagnetic storm, the ionosphere becomes turbulent - it heaves and scintillates, meaning signal strength fluctuates rapidly and unpredictably. Signal delays become irregular. The correction models that GPS receivers and WAAS rely on simply cannot keep up with what the ionosphere is doing in real time.

During the worst phase of the May 2024 storm, some GPS receivers in central Europe reported position errors of several miles. These were the most extreme cases and were short in duration, but they occurred.

How WAAS Works - and What Happens When It Fails Mid-Approach

The Wide Area Augmentation System (WAAS) is what makes LPV approaches possible. WAAS operates a network of precisely surveyed ground reference stations across North America. Those stations continuously measure ionospheric distortions and broadcast corrections to GPS receivers via geostationary satellites.

Under normal conditions, WAAS takes horizontal GPS accuracy from roughly 10 meters down to around 1 meter and vertical accuracy to below 3 meters - the precision that enables LPV minimums comparable to a Category I ILS.

When the ionosphere goes turbulent, WAAS integrity monitoring does exactly what it is designed to do. It detects that the correction data is unreliable, determines it cannot guarantee approach accuracy, and flags affected regions as outside the protection level. The GPS unit annunciates the problem. In Garmin equipment, the approach downgrades: LPV becomes LNAV/VNAV, or drops to LNAV only. Minimums change - in the middle of the approach.

If the weather was marginal for LPV but above LNAV minimums, the flight may continue. If it was marginal for LPV and below LNAV minimums, the pilot has a decision to make with limited time and limited options.

The FAA issued GPS NOTAMs throughout the May 2024 storm event. Those NOTAMs were technically in the system. They were also broad geographic warnings, issued with limited lead time, and changing rapidly as the storm evolved faster than models predicted.

Why This Matters: Solar Cycle Twenty-Five Is Not Finished

Solar Cycle Twenty-Five officially began in December 2019, as defined by the Solar Cycle Prediction Panel, a joint group from NOAA and NASA. Early predictions suggested an average or slightly below-average cycle. Those predictions were wrong.

Solar Cycle Twenty-Five has tracked above its predicted activity levels since roughly 2022. Solar maximum was expected around 2024 or 2025. The prediction community’s honest position is uncertainty - we may have already passed the peak, or may still be approaching it. What is clear is that the frequency and intensity of geomagnetic storms increases around solar maximum.

The May 2024 event was not an anomaly. There have been multiple G-3 and G-4 events in the twelve months before and after it. G-5 events are rare within any eleven-year cycle, but they are not impossible during this period - and aviation infrastructure has not fully adapted to this reality.

How Airlines Manage Space Weather - and Why GA Lags Behind

For airlines flying polar and oceanic routes, the operational response to major space weather events is relatively well developed. Major international carriers have contractual relationships with commercial space weather services. When a significant storm is forecast, dispatchers are alerted, polar routes are evaluated for rerouting, and alternate HF radio frequencies are pre-selected.

HF radio matters for oceanic operations because it is the primary voice communication method in airspace beyond VHF range. Solar flares produce intense X-ray radiation that ionizes the lower ionosphere on the sunlit side of Earth, absorbing HF radio waves at certain frequencies. During the May 2024 events, transatlantic HF communications were intermittently degraded across multiple frequency bands simultaneously. Some flights operating under reduced vertical separation minima on the North Atlantic Tracks had to request separation via datalink because voice communication was unreliable.

There is also a radiation exposure dimension. During significant solar particle events, high-energy protons accelerated by solar flares can reach Earth within minutes of a flare’s peak. For crews flying long-haul polar routes, the FAA Civil Aerospace Medical Institute has published research showing that career doses are meaningful when accumulated over years. During a major solar particle event, a single transpolar flight can expose a crew to a radiation dose comparable to several chest X-rays. Airlines with polar routes have operational protocols to descend and potentially divert when particle flux exceeds threshold values.

For general aviation pilots, this infrastructure does not exist. Space weather data is not integrated into standard FAA weather briefings. It does not appear in ATIS. It does not surface in ForeFlight or Garmin Pilot unless you actively seek it. That is a gap - and given the current phase of Solar Cycle Twenty-Five, it is a gap with operational consequences now.

Discussions are ongoing at the International Civil Aviation Organization about integrating space weather advisories into standard aeronautical meteorological products. NOAA has been building out the Space Weather Prediction Center’s data products and computational capacity. The European Space Agency has invested in space weather forecasting infrastructure through its Space Safety Programme. Progress is real, but integration into standard general aviation preflight tools is probably years away. Until then, the responsibility falls on the individual pilot.

What IFR Pilots Need to Do Differently Right Now

This is not primarily a technology problem. GPS receivers work correctly during space weather events. WAAS works correctly. Integrity monitoring detects degradation and annunciates it accurately. The problem is the gap between what the system knows and what the pilot knows before departure. That is an information architecture problem - and it is a solvable one.

Brief your alternate approach minimums before every descent when the forecast includes elevated geomagnetic activity. Know your LNAV minimums on every approach you brief. Do not assume the LPV you are planning will be available when you need it. This is the same logic that makes you brief the missed approach before you need it.

Maintain proficiency on non-GPS instrument approaches. During extreme events, it is not only the WAAS layer that degrades - basic GPS position accuracy can degrade as well. A GPS moving map is not an infallible source during active space weather.

If you fly regularly at high latitudes - Alaska, northern Canada, northern Europe - your exposure is higher. Ionospheric disturbances during geomagnetic storms are most severe in polar regions, where Earth’s magnetic field funnels charged particles from the solar wind toward the surface. The WAAS outage footprint during a G-5 storm concentrates at high latitudes first and spreads equatorward as storm intensity increases.

Where to Find Space Weather Data Before You Fly

NOAA’s Space Weather Prediction Center is at swpc.noaa.gov. The site is public and free. The three-day forecast products are operationally relevant and updated continuously. The planetary Kp index forecast is the most useful single number for general aviation purposes.

A Kp forecast at or above 5 (G-1 storm or higher) warrants awareness.
A forecast above 7 warrants active planning for alternate minimums and approach degradation.

SpaceWeatherLive.com provides a consumer-friendly version of the same data with real-time Kp readings and storm alerts. Spending two minutes on that page before an IFR flight to minimums costs nothing.

Key Takeaways

The May 2024 G-5 geomagnetic storm degraded WAAS GPS across North America and Europe, downgrading LPV approaches to LNAV minimums in real time - and arrived hours earlier than forecast.
Solar Cycle Twenty-Five has tracked above predicted intensity since 2022; we are at or near solar maximum, meaning elevated storm risk is ongoing, not historical.
When WAAS integrity monitoring detects ionospheric turbulence, it correctly flags the approach as unavailable - but that annunciation can arrive two miles from the runway.
Space weather data is not integrated into standard FAA briefings or EFB apps; pilots must check swpc.noaa.gov or SpaceWeatherLive.com as a separate preflight step.
The fix is not new technology - it is knowing your LNAV minimums, maintaining VOR/ILS proficiency, and treating a Kp forecast above 7 the same way you treat a marginal weather forecast: plan for degradation before you launch.