How is v-ta no used?

Question

Could someone explain the construction v-ta no? I saw it in the article title

東京などで雪　１１月に降ったのは５４年前

Answer 1

This の is a nominalizer, but more specifically, this can be understood as a marker that introduces cleft-sentences, which are used to focus some part of the sentence.

• (雪が) 54年前に 11月に 降った。
  Snow fell in November 54 years ago.
• (雪が) 11月に 降った の は 54年前だ。
  It's 54 years ago that snow fell in November. (54年前 is focused)

だ/です at the end is omitted because it's a news title which is expected to be short.

To be clear, this type of の does not have to follow the ta-form of a verb.

• この映画を初めて見ます。
  I see this movie for the first time.
• この映画を見るのは初めてです。
  It's the first time that I see this movie. (初めて is focused)

Answer 2

This の functions as a nominalizer of the sentence

東京などで雪が１１月に降った
Snow fell around Tokyo in November

The rest of the title talks about this sentence:

東京などで雪が１１月に降ったのは５４年前
Snow falling in and around Tokyo in November [was last] 54 years ago

or, more idiomatically,

The last time it snowed in November in and around Tokyo was 54 years ago.

Answer 3

There's not really a special construct going on here, just a sentence modifying a noun, and that noun being replaced by の due to reference locality.

In 「１１月に降った[の]{雪}は５４前」,「の」is used to refer back to 「雪」from 「東京などで雪」, modified by 「１１月に降った」.

As a whole, the headline reads roughly: "Snow in Tokyo and surroundings – First time in 54 years"