There are a number of software programs that will cruise the Web on your behalf and alert you when an aurora is likely. Several are mentioned in the article "Satisfy Your Auroral Longing."
The Space Environment Center of the National Oceanographic and Atmospheric Administration (NOAA) uses current satellite passes and statistical data to estimate the position and intensity of the auroral oval in close to real time. This is the best source for predictions of auroral activities in the short term. Their auroral map lets you check on the current state of Northern or Southern Hemisphere auroral activity to see if there might be a display this evening.
The Solar Terrestrial Dispatch page contains a wealth of information about what's going on in the near-Earth environment. Use this Web site to make your own auroral-activity forecast.
The Space Weather Bureau at NASA's Marshall Space Flight Center gives daily reports of geomagnetic activity and the probability of solar flares. The Bureau has branched into another medium with SpaceWeather Phone. Sign up for their service and, for a fee, they'll call you when things are happening in the sky, including displays of the northern lights.
The University of Alaska Geophysical Institute offers weekly auroral forecasts and real-time all-sky photographs when its camera is taking data.
Two other prediction tips are worth mentioning.
- Look the night after a good aurora is reported. Often magnetic storms last longer than 24 hours.
- Look 27 days after a major display; sometimes a region of solar activity lasts more than one solar rotation (which is about 27 days long) and comes around to aim at Earth a second time.