UPDATE – 9/27/2016 03:30 GMT (11:30 EST on 9/26)
SWPC has issued a continuation of the G2 aurora watch through September 30. There are now 72 hours of potential G2 storming predicted. NLN is starting up what promises to be a long duration live-blog post. As of midnight GMT on 9/27 here’s the 2nd and 3rd day AuroraCast forecast showing expected times for G2 storming, and the updated notifications timeline from SWPC.
Excited for this week!
Northern Lights Now – The return of a large coronal hole means the final week of September could be very good for aurora viewers. The Space Weather Prediction Center (SWPC) in Boulder, Colorado has issued a G2 geomagnetic storm watch for Wednesday September 28, when high speed solar wind from the coronal hole is expected to reach Earth. The watch means KP values could reach 5.67 or more. Coronal holes rotate around the Sun every 27-28 days, this is the return of the coronal hole that produced G2 storming from September 1st through 4th. Here is the current SWPC notifications timeline posting the alert:
Geomagnetic storm watches are posted for 24 hours periods. The peak aurora conditions could happen at any time within that period. The predicted timing is based on models that esitmate the of solar wind in interplanetary space and around Earth. There is always a level of uncertainty in predicting space weather. However, with returning nature of coronal holes, the forecasts come with more confidence. In fact, based on data from SDO and STEREO-A it was possible to predict that this coronal hole had survived the rotational cycle and that there there may be a watch posted more than a week in advance of the actual storm. Here is a tweet from NLN’s Twitter feed (please consider following us!) from last week
— Northern Lights Now (@NorthLightAlert) September 23, 2016
In the image below, see the same SDO wavelength image just three days later. As the CH rotates into view, it’s shape becomes clearer and more defined. This gives the space weather models a better chance of accurately forecasting when the high speed winds will arrive at Earth
As of this writing, there are two three hour periods of G1 storming predicted on 9/28 and one period of G2 storming. Given the long duration of this storm during the last rotation, it is very possible this watch will be extended over the next several days. Here is the current NLN AuroraCast graphic for day three: