Overview
- NOAA and the UK Met Office forecast a CH HSS-driven disturbance that is likely to raise geomagnetic activity to about Kp 4 late Tuesday, July 21, and near Kp 5 into Wednesday, July 22.
- NOAA’s predicted viewline covers 12 states including Alaska, Montana, North Dakota, Minnesota, Maine and northern parts of Washington, Idaho, Wisconsin, Michigan, New York, Vermont and New Hampshire.
- This event is driven by a coronal hole high-speed stream, not a coronal mass ejection, so forecasters expect a longer but generally milder storm with low risk of major infrastructure disruption.
- Actual visibility will hinge on the interplanetary magnetic field’s Bz orientation plus local factors like cloud cover, light pollution and short summer twilight that will make faint aurora harder to see.
- Observers should watch NOAA real-time aurora products and apps, choose dark north-facing sites between about 10 p.m. and 2 a.m., and use night-mode or long-exposure photography to reveal faint displays; longer warning lead times are expected in future from missions such as ESA’s HENON.