Many Alaskans will have a chance at viewing the aurora borealis tonight as the first of two massive bursts of solar wind en route to Earth interacts with the planet's magnetic field. The National Weather Service's Space Weather Prediction Center is forecasting Kp Index values to reach 5 by 6 (Friday) -- and possibly reach as high as 6 by early Saturday morning.
The Kp Index (ranging from 0-9) measures disturbances in the earth's magnetic field, with 1 being calm and 5 or more indicating a geomagnetic storm. The National Weather Service says a Kp Index of 4 is usually required for the aurora to be visible in the state's largest city, Anchorage. A Kp Index number of 5 or 6, coupled with clear skies in the forecast for Southcentral, means it's likely that Anchorage residents may be able to catch the northern lights this evening.
The Aurora Forecast posted by the Geophysical Institute at the University of Alaska Fairbanks gives Friday's aurora displays an "active" rating of 4 out of 10. The forecast writes, "Auroral activity will be active ... displays will be visible overhead from Barrow to Anchorage and Juneau, and visible low on the horizon from King Salmon and Prince Rupert."