During a strong geomagnetic storm watch, aurora activity can be seen well beyond the normal northern latitudes, at times extending as far as Alabama and Northern California. This, of course, is dependent on the strength of the solar energy coupling with the Earth’s magnetic field during the overnight hours and the darkness of the local skies.
The sequence starts at the sun. A geomagnetic storm is formed when a coronal mass ejection, or a solar plasma and magnetic field eruption, reaches the Earth and encounters the magnetosphere. This implies that the geomagnetic storm causes the expansion of the auroral oval, which moves the area of illumination to mid-latitudes, thus increasing the possibility of people witnessing aurora activity in an area where it is not normally seen.
This level of the event is close to the top of the range of scales that are used in the public domain. The NOAA Space Weather Scales classify the intensity of geomagnetic storms from G1 to G5; a G4 watch is the same as G4 Severe, which is usually associated with a Kp of 8. At this level of the event, aurora has been seen as low as Alabama and northern California, as long as there are favorable conditions. This level of the event also describes non-visible effects, which could be even more important than the visible effect: power grids could experience issues with voltage control; spacecraft could experience surface charging and tracking issues; and radio and navigation communications could become weak and intermittent. The key to remember for the real-world application of this event is not to fear but to be aware: the visible effect is the warning sign of a larger issue that could cause problems in the technologies that people use every day without even realizing it until something seems off.
In many instances, the timing will also help to further limit the possibility. Many good aurora prospects will occur around local late evening to early morning hours, and if the best coupling is during daylight hours, the display will likely be obscured from view. A aurora display does not have to be directly overhead to be viewed; during bright displays, it can be seen from as far away as 1000 km.
The forecast products provide important information that doesn’t need any knowledge. The short-term aurora forecasts are made by the OVATION model, which predicts the activation of the auroral oval based on solar wind data in the next 30-90 minutes. Moreover, the overnight outlook maps provide a “viewline” that indicates the southernmost points where aurora activity can be observed on the horizon at the forecast maximum.
Even in the conditions of strong space weather, the observation of the activity may be affected locally by clouds, haze, moonlight, and lighting. In the case of cameras, light is not a problem but a benefit. The night mode of smartphones uses the longer exposure time, and increasing the exposure time and the stability of the smartphone can help in detecting details that are not observable by the naked eye.
Severe storms are also a reminder that preparedness is a general topic, not a technical one. The National Weather Service space weather preparedness guidelines include activities such as preparing an emergency kit and developing a family communications plan, which are all good ideas even if the only effect of the storm is a goofy glow in the winter sky.
