The NOAA Space Weather Prediction Center has issued a G2 geomagnetic storm watch for April 20 UTC (8:00PM EST 4/19 – 8:00PM 4/20 EST), and a G1 storm watch continuing into April 21 UTC. This means we may see Kp values in excess of 6 the first day, and above 5 the second day.
Enlil model runs are predicting two waves of geomagnetic activity. The first wave is expected to peak around 5:00am UTC (1:00am EST), the second wave is expected to arrive about 12 hours later. As always, it is difficult to predict the exact time of CME arrival so either of the peaks could be +/- about six hours.
This timing is perfect for Iceland, most of North America, Southern New Zealand, Austrailia and Tazmania, Northern Russia, and the Scandinavian countries. The long duration of the potential event means all of those locations have a good chance of high KP values happening at or near magnetic midnight.
There were three Earth-directed Coronal Mass Ejections (CMEs) over the last 3 days. Every CME propagates through space at a different speed. Slower CMEs take longer, typically 3 days, to move from the Sun to Earth. Fast CMEs can arrive in as little as 24 hours.
The first CME contributing to this storm left the Sun late on April 15th. This CME was very slow moving and is likely to arrive at Earth in the first wave of geomagnetic activity. There’s a gap in the satellite data, so we can’t say for sure which sunspot region generated the CME, but it likely came from Active Region 2025.
The second CME is associated with the M1 solar flare late on April 16. This flare was located at Region 2035, classified beta-gamma at the time. The ejecta from this flare was moving faster and is expected to arrive around the same time as the CME from the first event.
Finally, the third, biggest, and fastest moving CME was released from Solar Region 2036 April 18th in association in a long duration M7.3 flare. This CME is moving so fast that is it likely that the matter ejected will catch up with the other two CMEs just before, or just after, all three CMEs pass Earth.
The third CME produced a strong asymmetrical full halo in LASCO imagery. In addition, the EPAM (pictured below – click to enlarge), reacted immediately. You can see the proton density increase almost simultaneously with the M7 flare at noon on the 18th. Following the initial shock, there is a consistent increase in the proton density. This indicates there is a CME moving directly toward Earth. We expect the proton density to continue increasing until the leading edge of the CME arrives at Earth. The higher it gets, the higher we expect Kp values to reach when the CME arrives.
Summed up, the geomagnetic events over the next 24 to 48 hours look very promising. Be ready to go out if the KP reaches levels high enough for you see see Aurora.