NOAA forecasts geomagnetic activity this weekend

NOAA’s Space Weather Prediction Center forecast minor to moderate geomagnetic storm conditions through Sunday and into Monday, a setup that can improve the chances of seeing the northern lights in parts of the United States. The agency’s May 16 forecast said the strongest expected three-hour Kp reading for May 16 through May 18 was 5.67, which corresponds to a G2, or moderate, geomagnetic storm. NOAA also said the strongest observed three-hour Kp over the prior 24 hours had already reached 6, also a G2 level. The forecast follows increased solar wind tied to a coronal-hole high-speed stream, according to NOAA forecasters. ### What exactly did NOAA forecast for this weekend? NOAA’s May 16 three-day forecast said G1 to G2 geomagnetic storms were likely on May 16, with G1 storm levels likely on May 17. The same forecast showed lower activity by May 18, when Kp values were expected to stay below storm thresholds even as unsettled conditions persisted at times. NOAA’s separate three-day geomagnetic forecast, issued late on May 15, put the probability of a minor storm at 35% on May 16 and 40% on May 17, with a 30% chance of a moderate storm on May 16. (swpc.noaa.gov) The Space Weather Prediction Center said the forecast was updated on a 12-hour cycle. Its plain-language forecast page said the product is issued at 0030 and 1230 UTC, while the geomagnetic forecast page provides deterministic Kp values and storm probabilities for the next three days. ### What is driving the geomagnetic activity? (swpc.noaa.gov) NOAA forecasters said a coronal-hole high-speed stream was behind the expected storm conditions. In the May 16 forecast, the agency said G1-G2 storming on May 16 was likely because of a corotating interaction region associated with a positive-polarity coronal-hole high-speed stream, with G1 conditions on May 17 due to that stream’s persistence. (swpc.noaa.gov) The agency’s forecast discussion issued at 0035 UTC on May 16 said solar wind conditions had already strengthened under the influence of a negative-polarity coronal-hole high-speed stream. NOAA said total interplanetary magnetic field strength rose as high as 17 nanoteslas during the period, while wind speeds increased from about 400 kilometers per second to near 800 kilometers per second by the end of the period. (swpc.noaa.gov) The discussion said enhanced solar wind parameters were expected to continue through May 18. ### Does that mean people in the U.S. could see the northern lights? NOAA’s aurora products say geomagnetic activity can shift the auroral oval farther south, improving visibility at lower latitudes when skies are dark and clear. The agency’s “Aurora for Tonight and Tomorrow Night” page says its North America outlook is based on the OVATION model and uses the maximum forecast Kp between 6 p.m. and 6 a.m. (swpc.noaa.gov) U.S. Central Time. It also says aurora can sometimes be seen from as far as 1,000 kilometers away when the display is bright and conditions are favorable. NOAA no longer publishes the old “viewline” on that experimental product. The agency says the page now shows forecast intensity and location over North America, while its 30-minute forecast provides a shorter-term outlook based on the time it takes solar wind to travel from the L1 observation point to Earth. ### How strong is a G1 or G2 storm in practical terms? (swpc.noaa.gov) NOAA classifies G1 as a minor geomagnetic storm and G2 as a moderate one. The May 16 forecast page said current impacts at the time included weak or minor degradation of high-frequency radio communication on the sunlit side of Earth and brief degradation of low-frequency navigation signals. (swpc.noaa.gov) The agency’s aurora dashboard showed G2 as the latest observed geomagnetic level over the prior 24 hours, with G1 predicted for May 16 UTC and May 17 UTC on the dashboard snapshot returned Saturday. That dashboard also listed a 40% chance of minor to moderate radio blackouts on May 16 UTC and a 5% chance of an S1 or greater solar radiation storm. (swpc.noaa.gov) ### Where should readers check before going outside? NOAA’s Space Weather Prediction Center says its aurora dashboard, 30-minute aurora forecast and three-day forecast pages are the main public tools for tracking conditions. The 30-minute product gives the shortest lead time, while the “Tonight and Tomorrow Night” page translates forecast Kp into a North America viewing map. (swpc.noaa.gov) May 18 is the last day covered by NOAA’s current three-day forecast window, and the agency said updated forecasts are issued every 12 hours. Readers checking conditions later Saturday or Sunday would need the newest SWPC updates, especially if cloud cover and local darkness line up with any renewed G1 or G2 intervals. (swpc.noaa.gov 1) (swpc.noaa.gov 2)