17 US states could see northern lights this week. Why not Arizona?

In April and May this year, Arizona residents reported an unusual, breathtaking sight in the night sky — a glimpse at the northern lights, also known as aurora borealis. Sightings of northern lights are becoming more common in the United States, but Arizona didn't make the list of 17 states that will be able to view these stunning skies this week.

The northern lights are most often seen in the earth’s northernmost regions as they extend out from the north pole, including in places like Alaska, Canada and Scandinavia, but they have recently been visible to people farther south. These lights are occurring more frequently as the sun reaches a point in its 11-year cycle known as a solar maximum.

This cycle increases the frequency and distance of the geomagnetic storms that lead to auroras, like the late April event when the northern lights could be seen as far as south Tucson. A wider range of the world will be able to view the stunning phenomenon for the next few years, but we are still at the beginning of the cycle as it will reach its peak in 2025.

Where are the northern lights visible in July?

On July 13, the northern lights could appear over 17 U.S. states if the weather conditions are clear.

The natural phenomenon is usually caused by solar winds coming from the sun and Earth's magnetic field, according to the National Oceanic and Atmospheric Administration's Space Weather Prediction Center.

The University of Alaska Fairbanks Geophysical Institute forecasts that auroral activity will be high this Thursday, causing highly active light displays that will be visible farther south than usual in these states:

• Alaska

• Montana

• North Dakota

• South Dakota

• Minnesota

• Wisconsin

• Michigan

• Maine

• Maryland

• New York

• New Hampshire

• Washington

• Vermont

• Idaho

• Oregon

• Wyoming

• Indiana

Why are the northern lights not visible in Arizona on July 13?

Although a strong geomagnetic storm is predicted on July 13, it may not be strong enough to expand into Arizona, according to Alex Young, a meteorologist at National Weather Service Phoenix.

"The more active the electrons are will determine how far south those lights will get," Young said. "Any particular time the northern lights can be seen in Arizona, it would have to be activity levels that are very rare."

The rare glimpse of the northern lights in Arizona this year was due to the severity of the geomagnetic storms where the auroras come from, according to the National Weather Service's Space Weather Prediction Center.

It starts when the sun's corona, or the outermost part of its atmosphere, releases a large amount of plasma and magnetic field, according to the weather service. This phenomenon is known as a coronal mass ejection, called CME for short.

When CMEs interact with Earth's magnetic field, this exchange causes geomagnetic storms.

Depending on a storm's severity, auroras can be visible farther south than usual. The storm that caused the northern lights to appear over Tucson was rated a G4, or severe geomagnetic storm on a scale of 1 to 5.

The geomagnetic storm occurring on July 13 has been predicted to be a G2 level, according to the University of Alaska Fairbanks Geophysical Institute, meaning it would be possible for the northern and eastern edge of the U.S. to see the northern lights.

Storms ranked as a category G4 or G5 would be able to be seen directly overhead at the northern edge of the U.S. and extend into the southern parts, such as Arizona.

When could Arizonans see the northern lights?

Because the solar maximum of the northern lights has not hit its peak yet, there are still many more opportunities within the next couple of years for Arizonans to see the green, red and blue lights without traveling far.

December 2019 marked the beginning of Solar Cycle 25. The cycle is categorized by the sun's natural 11-year cycle, when the sun shifts from relatively calm to stormy, then back again, according to NASA. When the sun is most active, it is freckled with sunspots and called the solar maximum.

These sunspots are associated with higher levels of solar activity, often the indicator that solar flares or coronal mass ejections are likely to occur. Those explosions spew matter into space, which reacts with Earth and causes auroras.

Scientists have forecasted that solar activity will peak in July 2025. As this approaches, more intense and widespread auroras will occur nationwide.

To keep track of when geomagnetic storms may occur and how far-reaching they may be, NOAA operates a short-term forecast with the location and intensity of auroras that is updated multiple times a day.

The Geophysical Institute run out of the University of Alaska Fairbanks also provides forecasts and detailed explanations about auroras.

This article originally appeared on Arizona Republic: Can I see the Northern Lights in Arizona? What to know