A very large sunspot issued five Earth-directed coronal mass ejections on Thursday, leading the NOAA Space Weather Prediction Center to issue a watch for G4 geomagnetic storm conditions Friday afternoon to Sunday. This is the highest alert category issued by NOAA since 2005.
A G4 storm on NOAA’s scale corresponds to a Kp index value of 8. Under these conditions, the northern lights or aurora borealis could be seen on the northern horizon as far south as Northern California and Alabama. Aurorae may be seen near to directly overhead the Pacific Northwest and Great Lakes with much of Canada (especially Western Canada) likely to experience significant displays.
Having five coronal mass ejections back to back is a remarkably rare event. Readers may remember a double-ejection event in March 2024. Coronal mass ejections are eruptions of material from the Sun, typically originating from sunspots. The sunspot area that generated these ejections is also remarkable – it is estimated to span an area 16 times the diameter of the Earth.
This size puts it on par with estimates of the sunspot area that generated the Carrington Event. While aurorae are typically confined to polar regions, this one in 1859 was strong enough to generate them well into the tropics. Reports of northern lights came in from places like Cuba, Hawaii, and Colombia.
The impeding solar storm is not the same strength as the Carrington Event despite having been spawned by a sunspot area of similar size. The Sun will rotate the current sunspot area to face away from Earth in the coming days.
Coronal mass ejections also create radio blackouts and problems with electrical grids. A G5 storm in 2003 caused power outages in Sweden and damage to electrical infrastructure in South Africa. A large storm in 1989 knocked out power to nearly all of Quebec.
https://ingallswx.files.wordpress.com/2024/05/img_2612-1.png?w=984HRDPS modeled cloud cover for 00:00 PDT Saturday. (WeatherBell)The weather in the Northwestern United States and Western Canada looks ideal for aurora viewing on Friday night. A few scattered high clouds are possible, along with spots of low-level stratus in some coastal areas, but mostly clear skies are forecast. This is thanks to a ridge of high pressure in place over the region.
If you’re in Canada or the northern half of the United States, you can improve your chances of seeing the northern lights Friday night by finding a dark location outside of a city or town with a clear view to the north. Aurora displays are also possible Saturday night.
Note that there is a level of uncertainty with these kinds of forecasts, just like those predicting “normal” weather conditions. Observed Kp numbers aren’t likely to exactly match the NOAA forecast but they should be close. Some uncertainty is also inherent in the timing of the solar storm.
Sunspot frequency varies based on the 11-year long sunspot cycle. Sunspots are the origin of events like this, thus having more sunspots present increases the chances of a geomagnetic storm producing aurora above Earth’s mid-latitudes.
The Sun is currently near the peak of its current cycle. The Space Weather Prediction Center notes that over the course of April 2024 there was an average of 137 sunspots present on the Sun compared to less than 1 for several months during the last minimum in 2019-2020 and 146 in February 2014.
February 2014 represents the peak of the last sunspot cycle. The ongoing maximum is forecast to continue to early 2026 before declining toward the next minimum. While sunspots, geomagnetic storms, and mid-latitude aurora are more common during the peak of the sunspot cycle, occasional storms do strike the Earth around the minimum.
The featured image is of an aurora display in Estonia in 2022. (MaximBilovitskiy/Wikimedia)
