The northern lights may be visible this Thursday, June 4, through Friday, June 5, from northern U.S. states and Canada after forecasters at the National Oceanic and Atmospheric Administration predicted up to G4-strength geomagnetic storms.

A bright waning gibbous moon will rise after midnight and brighten the pre-dawn sky, potentially interfering with faint aurora. It’s also worth stressing that space-weather forecasts often change rapidly.

According to NOAA , isolated periods of G1 geomagnetic storming are expected overnight on Thursday due to three separate sources of solar wind disturbances that may all reach Earth around the same time, increasing the chances of aurora.

On Friday, a G3 or even G4 geomagnetic storm could bring auroras to mid-latitudes, affecting as many as 23 states.

The U.K.’s Met Office advised that geomagnetic activity is expected to increase sharply on June 4, with G1–G3 (minor to strong) geomagnetic storm conditions (Kp 5–7) likely and only a very slight chance of isolated G4 (Severe; Kp 8) intervals. The Kp index measures global geomagnetic disturbance and provides a rough indication of how far from the poles aurora may become visible.

Northern Lights Alert: Triple Disturbance

Forecasters are monitoring a possible coronal mass ejection launched from the sun on May 30, a co-rotating interaction region (where fast solar wind compresses slower-moving material ahead of it) and a high-speed solar wind stream flowing from a hole in the sun’s corona (its outer atmosphere). Any one of these can trigger auroral activity, but when they arrive in close succession or overlap, their effects can reinforce each other, increasing the likelihood of geomagnetic disturbances — and aurora.

A series of X-class solar flares on the sun on June 3 were followed by two or even three CMEs, which are expected to reach Earth on June 5, according to Spaceweather.com . They came from a sunspot that unexpectedly began to erupt.

Northern Lights Tonight: Where And When

A G4 geomagnetic storm may mean the aurora is visible from many U.S. states, likely on the northern horizon. States with the potential to see northern lights include the northern parts of Washington, Idaho, Montana, Wyoming, North Dakota, South Dakota, Minnesota, Wisconsin, Michigan, New York and Maine. States farther south also with a chance include Oregon, Nebraska, Iowa, Illinois, Indiana, Ohio, Pennsylvania, Massachusetts, Connecticut, Rhode Island, Vermont and New Hampshire. However, states farther north will always have the best odds.

A useful way to see what may soon become visible in North America is to check aurora webcams around the world . It’s also worth checking SpaceWeatherLive.com , as well as apps such as Aurora Now, My Aurora Forecast, SpaceWeatherLive or Glendale Aurora, which provide live solar wind data.

Aurora Alert: Forecasting Aurora

The sun’s roughly 27-day rotation is a critical factor for predicting Northern Lights, as it brings active, aurora-producing sunspot regions back into view from Earth. However, 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: Understanding Intensity

Aurora-chasers frequently use the Kp index to predict the intensity of a geomagnetic storm, but for aurora displays, the crucial factor will be the orientation of the interplanetary magnetic field embedded within the solar wind. If its north-south component, known as Bz, turns southward (negative Bz), energy from the solar wind can couple much more efficiently with Earth’s magnetic field, allowing geomagnetic activity to intensify rapidly. A sustained southward Bz of −5 nT or stronger usually signals an imminent display of aurora.

Observers in northern U.S. states and much of Canada are on the cusp of a seasonal challenge — in the lead up to the June solstice, nights become very short, with twilight persisting for much of the night. That limits darkness and makes aurora more difficult to see — even if geomagnetic conditions become favorable.

Wishing you clear skies and wide eyes.