NOAA's Space Weather Prediction Center has issued a strong G3 geomagnetic storm warning for June 4 through to June 5, as multiple coronal mass ejections (CMEs) barrel toward Earth. Forecasters say some of the incoming eruptions may merge before arrival in a phenomenon known as a "cannibal CME," which could further intensify the storm's impact on Earth.This is great news for aurora chasers, as during G3 geomagnetic storm conditions auroras can become visible in mid-latitudes as far south as Illinois and Oregon, according to NOAA.The incoming storms were launched by a series of powerful eruptions from the active sunspot region 4455, which fired off an M9.3 flare, an M7.7 and an X1-class flare all within 24 hours of each other. NOAA forecasters anticipate the resulting CMEs to arrive at Earth from mid-to-late June 4 through June 5.When will the northern lights be visible? The best time to look for the northern lights will be after dark on June 4 into the early hours of June 5.According to NOAA forecasters, the strongest geomagnetic activity is expected during the evening and overnight hours, with G3 (strong) conditions possible between 2 p.m. and 5 p.m. EDT (1800-2100 GMT) and again between 8 p.m. and 11:00 p.m. EDT (0000-0300 GMT June 5).Moderate G2 storm conditions are expected outside these peak periods.