Northern Lights Alert: Where And When

A G1 geomagnetic storm may mean aurora seen from northern U.S. states overnight on Saturday, May 16, through Sunday, May 17, likely as a greenish or reddish glow on the northern horizon. That makes it important to be away from urban light pollution in the northern sky, with resources including a light pollution map and a catalog of Dark Sky Places particularly useful.

States with the potential to see northern lights include Alaska and (northerly parts of) Washington, Idaho, Montana, North Dakota, South Dakota, Minnesota, Wisconsin, Michigan and Maine.

If a G2-class geomagnetic storm erupts, aurora may be viewable from states farther south, such as Oregon, Wyoming, Nebraska, Iowa, Illinois, Indiana, Ohio, New York, Vermont and New Hampshire.

Northern Lights Alert: Coronal Hole

The forecast of aurora — for the third night in a row — comes in the wake of a coronal hole, a gap in the sun’s corona, its outer atmosphere. As a result, a fast-moving, turbulent solar wind is escaping from the sun and, crucially, coming straight at Earth.

“Active to G1 (Minor) storm levels are likely to prevail on 16-17 May due to lingering CH HSS influences,” reads a forecast from NOAA. That refers to the coronal hole and a resulting high-speed solar stream. Active levels are also likely on 18 May, 23 May, and 27 May as active regions of the sun turn to face Earth.

As charged particles interact with Earth’s magnetic field, it could spark a geomagnetic storm. As those particles accelerate down magnetic field lines at the north and south poles, they can create ovals of green and red.

Northern Lights Alert: Solar Activity

The geomagnetic activity comes after a recent pause. That’s normal. The sun’s roughly 27-day rotation brings active, aurora-producing sunspot regions back into view from Earth — and that’s exactly what’s happening now.

On May 7, an M2-class solar flare heralded the arrival of an active sunspot. A solar flare — an eruption of electromagnetic radiation — is caused by twisted magnetic fields, typically above sunspots. Sunspots are cooler, darker regions of the sun’s surface that form when clumps of its magnetic field well up from deep within the sun.

In the wake of the May 7 flare came several coronal mass ejections, clouds of charged particles that — if Earth-directed — can cause geomagnetic storms.

Northern Lights Alert: Forecasting Aurora

Calculating whether a CME is Earth-bound, and when it will arrive, can only be done accurately when the CME's effect on the solar wind — the stream of charged particles released from the sun that travels in all directions in the solar system — is measured by NOAA’s DSCOVR satellite, which orbits the sun a million miles from Earth. DSCOVR measures the solar wind’s speed and magnetic intensity, which is critical in calculating how it is about to change. Only then can an aurora display be accurately forecast by NOAA's Space Weather Prediction Center, but there's not much warning — just 30 minutes.

Northern Lights Forecast: Latest Updates

Aurora-chasers frequently use the Kp index to predict the intensity of a geomagnetic storm, but for aurora displays, the interplanetary magnetic field’s Bz component is more important. Bz determines how easily solar energy enters Earth’s magnetosphere. When Bz points north, Earth’s field resists it; when Bz swings south, the two fields connect, allowing plasma to stream in. A sustained southward Bz of −5 nT or stronger usually signals an imminent display of aurora.

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.

Wishing you clear skies and wide eyes.