The northern lights could become visible across parts of the northern U.S. this week as a fast-moving stream of solar wind from a large coronal hole reaches Earth.
Unlike some of the strongest aurora displays of recent years, this week’s event is not being driven by a coronal mass ejection. Instead, forecasters are monitoring a recurrent coronal hole, an area where the sun’s magnetic field opens into space and allows faster solar wind to escape.
Geomagnetic activity is expected to increase late on Tuesday, July 21 and continue into Wednesday, July 22. A G1-class, or minor, geomagnetic storm is considered likely, potentially bringing aurora into view from northern-tier U.S. states close to the Canada border.
The short summer nights (and this week’s first quarter moon) may make faint aurora harder to see, with lingering twilight reducing the contrast required to spot a glow low on the northern horizon. The forecast comes as noctilucent clouds are being seen in the northern hemisphere, and a comet brightens.
Northern Lights This Week
According to a forecast by space weather experts at the National Oceanic and Atmospheric Administration, “By late on 21 Jul, unsettled to active conditions are likely, with a chance for G1 (Minor) levels near the end of the period. By 22 Jul, unsettled to active periods are expected, with G1 (Minor) storm levels likely as the negative CH HSS moves into a geoeffective position.” A CH HSS is a coronal hole high-speed stream, a flow of fast solar wind that can disturb Earth’s magnetic field when it reaches a favorable, or geoeffective, position.
The UK Met Office’s Space Weather Operations Center is forecasting a similar scenario, stating: “The main feature of interest is a large, recurrent coronal hole which may give wind speeds around 450 km/s on Day 2 (21 Jul), increasing to 700 km/s on Day 3 (22 Jul), although with some uncertainty in timing.” The forecast adds that there’s an increasing chance of a G1 geomagnetic storm on July 21-22 as the anticipated coronal hole fast wind arrives.
The agreement between NOAA and the UK Met Office suggests forecasters expect a relatively modest space weather event, but enough to give observers across northern-tier U.S. states a chance of seeing the northern lights if skies are clear — and the solar wind’s magnetic field turns southward as it reaches Earth.
Northern Lights Forecast For The U.S.
A G1 geomagnetic storm can sometimes make the aurora visible from northern U.S. states, particularly from dark locations close to the Canadian border.
Potential viewing areas may include parts of Washington, Idaho, Montana, North Dakota, Minnesota, Wisconsin, Michigan, Maine, Vermont and New Hampshire. However, widespread visibility across the central or southern U.S. is not expected under the current forecast.
Aurora visibility will depend on the strength of the solar wind, cloud cover, local light pollution and the orientation of the interplanetary magnetic field. The latter, known as Bz, is one of the most important factors. When Bz points south, it can connect more efficiently with Earth’s magnetic field, allowing energy and charged particles to enter the magnetosphere. A sustained period of southward Bz could make the aurora brighter and push it farther south than expected. If Bz remains northward, however, the resulting display may be weak or restricted to higher latitudes.
Skywatchers should look toward the northern horizon during the darkest part of the night. A location away from streetlights and other sources of light pollution will offer the best chance of seeing faint aurora.
Aurora Alert: Latest Updates
Aurora forecasts can change quickly after a high-speed solar wind stream reaches Earth. To check visibility in real time, use NOAA’s 30-minute aurora forecast or download apps such as Aurora Now, My Aurora Forecast or Glendale Aurora for up-to-the-minute alerts and live solar wind data.
Smartphone cameras using Night Mode or a long-exposure setting may detect faint green, red or purple aurora before the colors become obvious to the naked eye.
Better Space Weather Forecasts May Be On The Way
Space weather is caused by activity on the sun, including solar flares and coronal mass ejections eruptions of magnetized plasma that travel through space. When these eruptions reach Earth on the solar wind, they can trigger geomagnetic storms capable of disrupting satellites, communications, navigation systems and power grids.
Space weather forecasts like this could become much more accurate within a few years. Presented at the Royal Astronomical Society’s National Astronomy Meeting this week in Birmingham in the U.K., the European Space Agency plans to launch its HENON CubeSat mission in early 2027 carrying MAGIC, a U.K.-built instrument designed to measure the solar wind’s magnetic field much farther from Earth than current spacecraft. Today, forecasters often have as little as 15 minutes to assess the severity of an incoming geomagnetic storm. HENON aims to increase that to as much as two or three hours, giving satellite operators, power companies and communications networks far more time to prepare for potentially disruptive space weather.
Wishing you clear skies and wide eyes.