We were in Voukatti, Finland for 10 days this past February. Voukatti is not as far north as Lapland. We had cloud cover for 9 of the 10 days.
Here is a northern lights resources:
Where do Northern Lights mostly occur?
The occurrence of auroras depends on the latitude of the observer. The
Northern Lights form an oval band around the magnetic poles of the
Earth. At a distance about 2500 km from these poles, the probability
for seeing auroras is almost 100 %.
The northern parts of Fennoscandia belongs to the maximum auroral
zone. In the coast of Ice Sea in North-Norway you will see auroras
almost every evening when the sky is clear enough. When moving
southwards, the frequency of auroras decreases. In Sodankylä every
second night is an auroral night, in Helsinki every 20th. These are
statistical rules giving the average extent of auroras. When the
Earth's magnetic field is very disturbed, the auroras can spread all
over Europe for a couple of hours.
The best time to see auroras is between 9 p.m. - 1 a.m. local time.
The best months are February - March and September - October. During
summer months you cannot see aurora due to light nights.