Hi, Ian.

In the Kingston, Ontario region our normal first snowfall (1cm) occurs
in the third or fourth week of October, though it can occur as early
as the first week of the October and as late as the first week of
November.

Our normal last snowfall (1cm)occurs in the third week of April,
though it has snowed as late as the third or fourth week of May. In
contrast, sometimes it does not snow again after the first week of
April.

The first "plowable" snowfall (5cm+) is usually occurs by the third
week of November, though it can happen as early as the second week of
October and as late as the first week of December.

The last "plowable" snowfall is usually in the last week of March or
the first week of April.

Between mid-March and mid-April the average daytime high increases
from +1 or +2C to +11C.

I guess that except for northern portions of the UK and higher
elevations further south, the occurrence of the first and last
snowfall is highly variable from places to place and from year to
year. I used to live near Philadelphia, USA where the first and last
snowfall (and total winter snowfall) could range widely from year to
year. This is less the case where daytime highs are often below
freezing for three months of the year up here in southern Ontario.

Cheers,

Bob