NOAA issues G2 geomagnetic storm watch May 15–16

The National Oceanic and Atmospheric Administration’s Space Weather Prediction Center forecast a G2, or moderate, geomagnetic storm for May 15-16 as a stream of fast solar wind reached Earth. NOAA’s public dashboard on Friday showed G2 conditions forecast for May 15 UTC, with G1 conditions forecast for May 16 and May 17. The agency’s three-day forecast said the greatest expected three-hour Kp index for the May 15-17 period was 5.67, which corresponds to G2 on NOAA’s scale. NOAA said the disturbance could produce auroras farther south than usual if geomagnetic conditions strengthened overnight. ### What exactly did NOAA forecast for the night of May 15-16? NOAA’s Space Weather Prediction Center said on May 15 that “G2 moderate” geomagnetic storm conditions were predicted for the May 15 UTC day. The same NOAA forecast products showed a step down to G1, or minor, geomagnetic storm conditions for May 16 and May 17 UTC. The three-hour Kp index is one of the main public measures used to describe geomagnetic activity, and NOAA’s May 15 forecast put the peak expected value at 5.67. (swpc.noaa.gov) On NOAA’s scale, that is enough for a G2 classification. ### What was driving the storm? NOAA’s forecast products and related space-weather reporting pointed to a high-speed solar wind stream tied to a coronal hole on the sun. (swpc.noaa.gov) SpaceWeather.com reported that a co-rotating interaction region had already reached Earth and that faster solar wind behind it could push conditions from G1 to G2. NOAA’s enthusiast dashboard on May 16 showed solar wind speeds in the roughly 658 to 738 kilometers-per-second range. (swpc.noaa.gov) A February NOAA storm alert described the same kind of setup, saying G2 levels were likely associated with a coronal-hole high-speed stream and noting winds above 700 kilometers per second at L1, a monitoring point between Earth and the sun. That alert was for a different event, but it described the same mechanism NOAA forecasters were tracking in mid-May. (spaceweather.com) ### How far south could the aurora move? NOAA’s aurora dashboard is the agency’s public tool for checking whether the auroral oval is expanding southward in near real time. The dashboard does not list states in the excerpt available here, but NOAA says stronger geomagnetic storms can make auroras visible at lower latitudes than usual, depending on cloud cover, local darkness and how the storm develops. (swpc.noaa.gov) SpaceWeather.com said high-latitude auroras were favored as the solar wind arrived, while broader public reports on Friday cited chances extending into parts of the northern United States if the storm reached the upper end of NOAA’s forecast range. NOAA’s own products advised users to monitor the aurora dashboard for the latest viewline and short-term forecast. (swpc.noaa.gov) ### Did moonlight help or hurt viewing conditions? May 16 brought a new moon, reducing moonlight during the overnight viewing window in North America. Timeanddate.com’s May 2026 lunar calendar lists the new moon on May 16, including a U.S. time of 3:01 p.m. for U.S. territories, which means the moon was effectively absent from the night sky for much of the aurora window. (spaceweather.com) Dark skies do not guarantee visibility. NOAA’s aurora products and public guidance still depend on the storm’s intensity, local weather and whether the auroral oval expands far enough south to reach a viewer’s horizon. ### What disruptions can a G2 storm cause besides auroras? NOAA’s public dashboard said weak or minor degradation of high-frequency radio communication was possible on the sunlit side of Earth, with occasional loss of radio contact. (timeanddate.com) The same dashboard said low-frequency navigation signals could be degraded for brief intervals. (swpc.noaa.gov) NOAA’s alerts, watches and warnings page says its bulletins are intended to describe expected impacts from solar activity on Earth’s environment. For this event, the agency’s public-facing products pointed to communications and navigation effects rather than major infrastructure disruption. ### Where should people check next? (swpc.noaa.gov) NOAA’s Space Weather Prediction Center updates its homepage, aurora dashboard and three-day forecast as conditions change. The May 16 forecast cycle was already posted early Saturday UTC, and NOAA’s dashboard continued to show real-time solar wind and geomagnetic readings as the event unfolded. (swpc.noaa.gov 1) (swpc.noaa.gov 2)