Here are links to the pages, which I've found to be most useful in trying to observe aurora in central and northern Finland. Many other great sites exist, but it makes sense for an amateur to concentrate on a few selected sources and learn how to best interpret their information.

None of these sites is infallible alone, but by combining their data one may be able to get quite close to the truth and be at the right spot at the right time to witness the celestial light show.

SEC's Report of Solar-Geophysical Activity

• A systematic and reliable report of solar and geophysical activity from the leading U.S. authorities, covering the past 24 hours, and including a forecast for the next three days.

Spaceweather.com News Bulletin

• An easy-to-read summary of recent events in the Sun-Earth environment, solar activity and probabilities of spotting aurora. The left-hand column contains real-time solar wind data, including the most recent solar flares. Also included are forecasts for coming solar eruptions and geomagnetical activity.
• There are three equally important parameters to observe: solar wind speed (V_sw), its particle density (D_sw), and the B_z component, which indicates the direction of the Interplanetary Magnetic Field: a minus means the field is pointing south and the 'doors are open' for the solar wind particles to enter the Earth's magnetosphere, whereas a plus means the field is pointing north and 'the doors are closed' for the aurora process to develop.
• Roughly, a speed higher than 400 km/s and a minimum density of approx. 10 particles/cm³ are quite promising figures.
• After a geomagnetic storm aurora photos from around the world are on display at the 'Aurora Gallery'.

Costello Geomagnetic Activity Index

• The so-called Costello index aims to predict the Earth's geomagnetic activity, and thus also the development of aurora activity, for the next three hours. When the Kp index rises above 4 (on a 0...9 scale, storm level =5), there's ample reason to check the northern sky in central Finland as well.

Sodankylä Observatory Magnetogram

• One cornerstone for observing aurora in Finland is the reading of the Sodankylä Geophysical Observatory magnetogram, located in Finland's central Lapland. When the topmost X-component graph is on a brisk rise early in the evening, several hundreds of nT (nanotesla), the circumstances for aurora are getting good.
• Later in the evening, if the X-component reading decreases rapidly, several hundreds of nT, an aurora show has just begun. The larger the drop, the farther south aurora will be visible.

Solar Wind Data From SOHO Spacecraft

• The parameters to observe here are the same as the key ACE satellite data delivered by Spaceweather.com: solar wind speed (V_sw), particle density (D_sw), and the direction of the Interplanetary Magnetic Field (B_z).
• The SOHO spacecraft observes solar wind shock waves 1 to 2 hours before their arrival at Earth. The data is reliable even during magnetic storms.

Statistical Aurora Oval Maps

• Graphical interpretations of the so-called statistical aurora ovals, based on NOAA satellite measurements and statistical counting. The ovals indicate how widely spread the auroras are, and their activity level (blue 0...red 10).
• If early in the evening the northern oval over Siberia looks expanded and is colored orange or even red, activity level being 8...10, the probability is high that an aurora enthusiast in central Finland will have to spend the night out.

Auroras Now!

• Auroras Now! is a service which helps spotting auroras in Finland. The Finnish Meteorological Institute maintains the service, which includes magnetic field alarm systems for Northern and Southern Finland separately and an auroral monitor for Northern Finland.

Weather Forecast From the Finnish Meteorological Institute, Weather Forecast From Foreca (Finland)

• Finally, a simple reminder of perhaps the most critical factor for spotting aurora: ground weather conditions. Even today the fact is that weather at the observation point has to be quite clear, because the faint aurora light can not be seen through clouds.
• Quite often the situation is nerve-wracking: an aurora storm is about to start, but the sky above you is totally cloudy. Naturally, this means packing your gear into a car and driving to a place where the sky is as clear as possible.
• However, a perfectly clear sky is not a necessity for an unforgettable aurora night, since a cloud here and there just create a fine three-dimensional effect, to photographs as well.
• These weather forecast sites will help you in your search for a suitable location in Finland.

Rain and cloud areas over Scandinavia

• This animation from the Finnish Meteorological Institute will help you determine where you might spot a piece of clear sky next.

The rest depends on one's own activity level ;-)