A Carrington-class event is a geomagnetic storm on the scale of the one in 1859. It is a natural hazard, not a prediction for 2027. The sources give odds and impacts with wide uncertainty, and the honest answer to "when" is that nobody knows.
What the sources say
NOAA's scale. NOAA's Space Weather Prediction Center rates geomagnetic storms from G1 to G5. A G5 (Extreme) storm corresponds to Kp 9. NOAA says grid voltage control and protective systems can fail widely, some grids may collapse, "transformers may experience damage," and satellites may suffer extensive surface charging and tracking problems. On average, G5 storms occur about 4 days per 11 year solar cycle.
May 2024. NOAA rated the 10 May 2024 storm G5. Press reports described it as the first G5 since October 2003. We could not open NOAA's own comparison page, so treat that detail as reported.
Lloyd's, 2013. Lloyd's report "Solar Storm Risk to the North American Electric Grid," with Atmospheric and Environmental Research, is described in coverage as estimating that 20 to 40 million Americans could lose power for 16 days to two years, at a cost of $600 billion to $2 trillion, with return periods of about 50 years for Quebec level storms and about 150 years for very extreme storms. Outage length depends largely on spare transformers. These figures come from secondary coverage, and critics argue the modelled storm was closer to 1989 than to 1859. We did not read the full report.
What is affected
Power grids (via induced currents in long conductors and transformers), satellites (drag, charging), GPS timing and radio. Data centres and networks depend on all of these.
How to check if you're exposed
- Identify which systems rely on GPS time or satellite links.
- Find out how long your site and your cloud providers can run on backup power.
- Check whether any critical vendor sits in one region.
What to do now
- Document power and fuel assumptions for key sites.
- Keep offline copies of runbooks and contact lists.
- Make sure time sync has a fallback source.
- Test recovery from backups in another region.
Why it matters
The odds are low in any single year and the effects uncertain, but the planning steps match those for ordinary regional outages. NOAA gives forecasts only hours to days ahead.
Try it yourself
Pick your most important service and write down what happens after 72 hours without grid power at your main provider region.
Quick check
How often does NOAA say G5 storms occur?
On average about 4 days per 11 year solar cycle.
Is a Carrington-class storm predicted for 2027?
No. No source we found gives a date. Return periods in the Lloyd's study are long term estimates, not forecasts.
