How Snow Is Formed

Snow is formed when temperatures are low and there is moisture - in the form of tiny ice crystals - in the atmosphere. When these tiny ice crystals collide they stick together in clouds to become snowflakes. If enough ice crystals stick together, they'll become heavy enough to fall to the ground.

How cold does it have to be to snow?

Precipitation falls as snow when the air temperature is below 2 °C. It is a myth that it needs to be below zero to snow. In fact, in this country, the heaviest snow falls tend to occur when the air temperature is between zero and 2 °C. The falling snow does begin to melt as soon as the temperature rises above freezing, but as the melting process begins, the air around the snowflake is cooled.

If the temperature is warmer than 2 °C then the snowflake will melt and fall as sleet rather than snow, and if it's warmer still, it will be rain.

'Wet' snow vs. 'dry' snow

The size and make up of a snowflake depends on how many ice crystals group together and this will be determined by air temperatures. Snowflakes that fall through dry, cool air will be small, powdery snowflakes that don't stick together. This 'dry' snow is ideal for snow sports but is more likely to drift in windy weather.

When the temperature is slightly warmer than 0 °C, the snowflakes will melt around the edges and stick together to become big, heavy flakes. This creates 'wet' snow which sticks together easily and is good for making snow men.


Snowflakes are collections of ice crystals that can occur in an infinite variety of shapes and forms - including prisms, hexagonal plates or stars. Every snowflake is unique, but because they join together in a hexagonal structure they always have six sides.

At very low temperatures snowflakes are small and their structure is simple. At higher temperatures the individual flakes may be composed of a very large number of ice crystals - making a complex star shape - and can have a diameter of several inches.


- Due to its geographical location and exposure to Polar air streams, Donegal is Ireland’s snowiest county on average. In contrast, southern and southeastern coastal counties experience the least snow.

- One of the heaviest snowfalls ever recorded in Ireland occurred not in winter, but in mid-Spring, when up to 2 foot of snow fell in parts of Connacht and north Munster in the space of a few hours on the 1st April 1917.

- The winter of 1946-1947 is probably the snowiest winter on record in Ireland and although the winter of 62-63 was infamously cold, relatively little snow was recorded overall during that season.

- Although January 1982 is famed for bringing heavy snowfalls along parts of the east coast, less documented is the fact that equally heavy and disruptive snowfalls affected many parts of Ulster, Connacht and north Leinster during the previous month (December 1981)

- Based on Met Eireann data, the number of days with observed falling and lying snow in Ireland has decreased by around 10% since 1961.

Info c/o The Meteo Times/UKMO