Update 11/18/2015
SWPC has increased the official G1 storm watch period to two days. They are now calling for 36 hrs of KP=4+ with a 15 hrs period of KP=5+ possible. You can see the updated forecast on the NLN 3-day AuroraCast Clock, and track the KP live on our current KP real-time chart.
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Original post
Spaceweather forecasters are sure there will be some geomagnetic effects, including aurora, from recent activity on the Sun, but won’t know how much until the solarstorms arrive at Earth. Aurora hunters should be alert for the possibility of a good show. The forecast is complicated because there were multiple events on the Sun over the last few days and the models have produced varied results. The official forecast is for about 6 hours of G1 storming (KP=5) on Wednesday, but it could be more… or less.
On November 15, a minor coronal hole was pointed towards Earth. The high speed wind stream from that hole is expected to arrive on the 18th. This is a new CH so there is no historical data on how strong the wind stream will be. Here’s an image of that coronal hole (the dark area center-Sun in the northern Hemisphere):
Then, on November 15 & 16, a pair of filament eruptions launched from just south and west (to the right) of the coronal hole. The first was 21 degrees long, the second was 19 degrees, both produced CMEs. LASCO imagery appears to show a miss to the SW for the first filament, and a slight partial halo for the second. A partial halo means the CME may hit Earth with a glancing blow. Here’s a zoomed in image of the pair of filament eruptions in SDO AIA 304:
All together, the events make a complicated forecast. The high speed stream alone could produce G1 storming, or it may barely be noticeable as it arrives. The first filament will likely not impact Earth as it’s ejecta is too far west. The second filament on it’s own likely would only have a minimal impact – WSA Enlil modeling is showing a low density on arrival. However, if the high speed stream is moderately strong, it could activate the magnetosphere to the point where any disturbance, including the glancing blow, could elevate KP readings to G2 level.
The take home message: aurora hunters have to wait and see. There’s a chance that KP=4 is the highest it gets in this storm, or it could reach KP=6. Keep your camera gear ready, prepare for disappointment, but hope for the best.
Happy Hunting!