When is the famed lemming year going to happen in Finland? When was the last one?

From what I’ve got from a bit of research is that Finnish lapland has 2 lemming species. Most notable is the Norway lemming who lives in the alpine zone on fells in the deep north of Lapland province. Sources say that every 30-35 year Finland has one of the most major surges of lemmings seen anywhere in any arctic regions where they travel in colossal numbers all the way down to the golf of Bothnia and Lapland’s southern border. When did this happen last? I found sources talking about an event in the 60s but i couldn’t find one referencing a time after that. Knowing when the last one happened when will the next? Also does anyone know how regular and of what scale smaller scale migrations are?