Based on Empirical Space Weather Forecast Tool by University of Graz.
SDO image courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.
SDO 193 Å EUV Image
NOAA SWPC Syntopic Map
DunedinAurora.NZ computer generated CH Map
Coronal holes are natural openings in the solar atmosphere that allow fast flowing streams of solar wind to fan out. When these streams hit the earth they squish our magnetic field and can cause auroral displays. There is a correlation between the size of a coronal hole and the intensity of the solar wind hitting the Earth. At Dunedin Aurora, we have created a computer program that calculates this relationship between coronal hole size to solar wind speed. Once we know this, we can calculate the arrival time of any space weather strong enough to cause an aurora.
Linear approximation is: Predicted windspeed = 394.15 + 423.12 * coronal hole area on meridian
Pearsons correlation |r| = 0.3060
Average Windspeed is 415.7km/s
Space weather transit time is 4.2 days