Northern Lights May Be Visible Over PA: When To Watch

PENNSYLVANIA — Pennsylvanians could catch a sight of the Northern Lights Saturday night as the National Oceanic and Atmospheric Administration has issued a geomagnetic storm watch for Saturday, noting that the aurora could be visible as low as Pennsylvania to Iowa to Oregon.

The storm is classified as a "G3" or "strong" on the Space Weather Prediction Center's five-point scale, and previously the aurora has been seen as low Illinois and Oregon with a storm of that strength.

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NOAA explains the storm watch was issued as a response to a coronal mass ejection on Thursday, which the agency says "are large expulsions of plasma and magnetic field from the Sun’s corona."

The forecast in the Philadelphia area calls for heavy rain into Friday night, and more rain later on Saturday night, with cloudy skies in some areas potentially obscuring the view.

Light pollution can also make the aurora difficult to spot, and the best bet for viewing is to get away from the city to somewhere with a clear view of the northern horizon.

The Space Weather Prediction Center has a handy explainer for the conditions needed in a particular location to actually be able to see the aurora. Depending on a viewer's magnetic latitude, the geomagnetic activity over a three hour period — measured on a scale from 0-9 — needs to reach a certain threshold for it to be visible.

The prediction center says to pick a city closest to the viewer and note its magnetic latitude. Based on the latitude, the center says to check this map to see how high the geomagnetic activity (Kp) needs to be.

For example, the magnetic latitude of the city closest to Philadelphia is New York (50.6). The Kp needs to be at least 7 for the aurora to be visible that low. At present, NOAA expects a Kp of between 6-7 Saturday night, which should be enough for visibility. Space officials say viewers should check the Kp activity before heading out.

However, the Space Weather Prediction Center cautions that skies also need to be favorable with no interference from the moon or city lights.

Feroze Dhanoa and Lucas Combos contributed reporting and writing for this report.