SWPC has posted a G1 for late July 31 and early August 1, 2015. This watch is due to the arrival of a high speed solar wind stream coming from a group of coronal holes pointed towards Earth. The predicted peak of activity coincides almost directly with the second full Moon of July, a blue moon, which will make viewing aurora difficult unless this proves to be a very strong storm.
The three coronal holes that are contributing the predicted increase in solar wind speed are visible in the combined 211, 193 and 171 wavelengths from July 29. In this image taken by the SDO observatory NLN has added arrows pointing to the coronal holes that appear as dark areas.
Generally, increases in solar wind speed is are more predictable coming from coronal holes. They rotate with the Sun and so solar scientists have data from the previous rotation. Additionally, the flows out from a coronal hole are more consistent and even than in a solar flare. Together, these give forecasters higher than normal confidence in the models and predicted timeline. For this solar storm, SWPC is predicting KP=5, or G1 storming, in the final 3-hour period of 7/31, and the first 3-hour period of 8/1. This timeline translated to between 5PM to 11pm on July 31 central time.
This image shows the predicted 3-hour maximum KP values for the two days of the current storm watch (click image to enlarge)
The storm will coincide almost directly with the full Moon. This is the second full Moon of July making it the first Blue Moon since August 20, 2013. While that is neat and interesting, the full moon will brighten the entire sky and will make viewing this aurora difficult.