NOAA forecasters see minor geomagnetic storms as likely on November 17-18 and 27-28

Forecasters at NOAA's Space Weather Prediction Center see minor geomagnetic storm levels, G1 on the agency's five-step scale, as likely on November 17 and 18 and again on November 27 and 28, according to the center's weekly forecast issued at 02:58 UTC on November 9, 2026. They see G1 levels as likely once more on December 4 and 5. The center attributes the expected activity to coronal hole high-speed streams, fast solar wind flowing from dark regions of open magnetic field in the Sun's corona. All dates here are in UTC, as the center gives them.

The center's 27-day outlook, issued the same day, puts the largest Kp index at 5 on each of those six days, against 2 or 3 on most other days through December 5. These are forecasts, and the center issues a fresh outlook every Monday.

What a G1 storm means for skywatchers

Kp measures disturbance in the horizontal part of Earth's magnetic field on a scale of 0 to 9, over three-hour periods, averaged from 13 observatories between 44 and 60 degrees geomagnetic latitude; 5 or more counts as a storm. NOAA's scale sets G1 at Kp 5. At that level, the scale says, auroras are commonly visible at high latitudes, naming northern Michigan and Maine. At G2, or Kp 6, it says auroras have been seen as low in latitude as New York and Idaho, typically around 55 degrees geomagnetic latitude. The scale itself names only places in the United States, alongside geomagnetic latitudes.

A minor storm can also cause weak power grid fluctuations and minor effects on satellite operations, according to the scale, which says such storms occur about 1,700 times in an average 11-year solar cycle, spread over about 900 days. The center issues a watch when the highest Kp forecast for a day reaches 5, a warning when it expects Kp of 4 or more, and an alert when Kp actually reaches 4 or more.

A 27-day rhythm

Coronal holes are cooler, less dense regions of the Sun's corona where open magnetic field lets the solar wind escape faster, the center explains. The longer-lived ones can sometimes survive several of the Sun's roughly 27-day rotations, and their streams can push Earth's field to G1 or G2 levels, occasionally higher.

The new dates fit that rhythm, by our count. NOAA's alerts recorded Kp 5 at 23:59 UTC on October 21, Kp 6 at 19:14 UTC on October 31 and Kp 5 again at 01:17 UTC on November 1, then Kp 5 at 19:45 UTC on November 7 and 02:03 UTC on November 8. Each forecast pair falls 27 days after one of those stretches. The center attributed the November 7-8 storm to a coronal hole high-speed stream; its forecast does not say which earlier storms it expects to recur, so that link is our inference.

Flares and the solar cycle

The Sun also flared last week. Region 4566 produced seven M-class flares between November 2 and 8, the largest an M3.5 that peaked at 18:33 UTC on November 5, according to the center. A coronal mass ejection that came with it was heading too far east to affect Earth. The center expects the region to rotate out of view on November 14 and to return around November 28, when moderate flare levels and a slight chance of a minor radiation storm return with it.

Sunspot numbers are lower than a year ago. In data the center publishes, the monthly mean international sunspot number from S.I.D.C. in Brussels was 45.7 for October 2026, against 114.8 in October 2025; the center's own monthly mean count, from its Space Weather Operations observations, was 61.7, against 107.1. Both October 2026 figures are preliminary, as the center treats every value from the latest six months. On the international series, the highest smoothed value from 2009 onward is 160.9, for October 2024. Those comparisons are ours, from the center's data. The center expects the next cycle, Cycle 26, to begin between January 2029 and December 2032.

How the warnings reach forecasters

The center said on June 30 that NOAA's SOLAR-1 observatory, short for Space Weather Observations at L1 to Advance Readiness, had become its primary source of solar wind data, with the ACE spacecraft as backup until IMAP's I-ALiRT system has 24/7 coverage, and that it had stopped processing DSCOVR data. SOLAR-1's Compact Coronagraph 2, the last of its instruments to be declared operational, reached that milestone in June, and the center said on July 23 that the observatory as a whole was now operational. The next 27-day outlook is due by 15:00 UTC on Monday, November 16. Our guide to the late November sky covers the month's other sights.