How extreme could a solar storm get?
The short version
Every geomagnetic storm SolarStormAlert has ever reported on has topped out at G5 (Extreme) — the ceiling of NOAA’s own scale. Two historical reference points sit above what any storm in the modern satellite era has produced: the 1859 Carrington event and the 774 AD “Miyake” event, named for the physicist who first identified its signature in tree-ring radiocarbon data. This piece states what is actually known about both — magnitude and likelihood together, each figure carrying its own cited uncertainty range — and what SolarStormAlert does if conditions ever move in that direction.
How rare is a Carrington-class event
The 1859 Carrington event is the best-documented severe geomagnetic storm in the instrument era, estimated at roughly X45 in flare terms. Published space-weather research estimates the recurrence rate for a storm of that scale at roughly once every 100 to 200 years — genuinely rare within a single lifetime, but not implausible: Solar Cycle 25’s declining phase, 2026–2028, is the historical window when the largest G4+/G5 events have tended to land, based on the pattern from Cycles 23 and 24 (NOAA Space Weather Prediction Center Solar Cycle 25 progression). Magnitude and likelihood, stated together: a storm of this scale is physically well-characterized, and genuinely uncommon.
How rare is a Miyake-class event
The 774 AD event is an order of magnitude larger again. Its flare magnitude is estimated at ~X230–X285 — peer-reviewed, high-confidence work published in The Astrophysical Journal (IOPscience) — with X255 as the midpoint of that cited range, not a settled figure in its own right. Events at this scale are exceedingly rare: the tree-ring radiocarbon record shows only two well-documented occurrences, 774 AD and 993 AD. No instrument existed to measure either directly; every physical estimate for them — flare class, associated geomagnetic response — is reconstructed from indirect evidence, and every number below carries that same reconstruction-based uncertainty.
For context on scale: Carrington’s ~X45 and Miyake’s ~X230–X285 are separate, distinct ranges — the Miyake range sits roughly 5–10 times higher, not a variant of the same event class.
What “extreme” means in physical terms
NOAA’s G-scale tops out at G5 (Extreme) — Kp 9.0 and above — which is the geomagnetic response level associated with a Miyake-class event’s reconstructed magnitude. G5’s documented, source-cited effects (the same definitions this dashboard’s Kp/G-scale glossary uses): grid systems may experience voltage control problems and protective-system trips, some grids may experience complete collapse or blackouts, and aurora becomes visible at unusually low latitudes. The step below, G4 (Severe) — Kp 8 — is documented separately: widespread voltage control problems possible, protective systems may mistakenly trip parts of the grid, but full collapse is not part of G4’s documented effect set. A Carrington- or Miyake-class event sits at or above the G5 threshold, not partway into it; there is no higher NOAA rung to place it on.
What SolarStormAlert does about it
SolarStormAlert delivers this today as a free email alert: subscribe at a G-scale floor of G3, G4, or G5, and a source-cited notification arrives the moment NOAA’s own G-scale call crosses that floor — the same alert path for a Carrington- or Miyake-class event as for any other G5 crossing, since both sit at or above the G5 threshold already covered, not a separate “extreme event” tier with its own rules. Mobile push notifications, including a planned iPhone Critical Alert option for premium subscribers, are not part of that alert path yet; per the how it works page, push delivery is planned for a future release. The dashboard’s live Kp reading and forecast are always one tap away, sourced directly from NOAA SWPC.