The G4 (Severe) geomagnetic storm watch is now in effect for 1 and 2 June. A powerful coronal mass ejection (CME) erupted from the Sun the evening of 30 May. Confidence in an Earth-directed component is good, but the CME arrival timing is more uncertain due to the current state of the solar wind. It could arrive as early as late morning EDT, to as late as Sunday evening EDT of 1 June. The center of the bulk CME material is anticipated to be just north of Earth, however, Earth will still likely undergo passage of much of the CME material. Arrival will likely lead to immediate geomagnetic disturbances with the potential for G4. Conditions will likely intensify as CME progression continues and G4 levels remain possible on Monday, 2 June. Geomagnetic storm levels will likely begin subsiding by Tuesday, 3 June, with G1-G2 (Minor-Moderate) still possible. These watches represent potential based on our best analyses. We will not know the true nature of this CME’s geomagnetic storm potential until the CME arrives at our solar wind observatories located 1 million miles from Earth. Upon arrival at those spacecraft, we will know the magnetic strength and orientation that are very important to what levels and duration of geomagnetic storm conditions are expected to occur and any appropriate warnings may be issued. As always visit our website for the latest information and updates.