NOAA’s Space Weather Prediction Center (SWPC) reports that geomagnetic storm watches are in effect through December 11, due to the effects of a direct coronal mass ejection (CME) collision with the Earth’s magnetosphere from December 9 until December 11. The CME eruption was associated with a C7 solar flare erupting from Sunspot Region 2790 on December 7.

Arrival of a shock wave associated with the CME is possible late on December 9, initially resulting in a G1 (minor) geomagnetic storm. As CME effects continue, geomagnetic disturbance is likely to increase, especially if the magnetic field carried with the CME rotates to a southward orientation, causing magnetic reconnection with Earth’s opposite polarity magnetosphere. The potential for stronger storm levels exists, and a G3 (strong) geomagnetic storm level watch is in effect for December 10. A G3 storm level can result in intermittent HF radio conditions, with the possibility of aurora borealis appearing as far south as Illinois and Oregon.

CME-related geomagnetic disturbances are forecast to continue through December 11, likely resulting in G2 (moderate) geomagnetic storm levels; another geomagnetic storm watch has been issued accordingly. In a G2 storm, HF radio propagation can fade at higher latitudes, and aurora has been seen as far south as New York and Idaho.

While SWPC forecasters are fairly confident that the CME will arrive at Earth, the timing and geomagnetic storm intensity are less certain. Visit the SWPC Current Space Weather Conditions web page for updates. (See also www.solarham.net/geo_forecast.htm and www.swpc.noaa.gov/products/wsa-enlil-solar-wind-prediction.)