Snow fall examples
This chart shows high pressure centred over Scandinavia with cold air from Eastern Europe affecting the UK. It had been a very cold week before the Atlantic weather front attempted to cross the UK from the west. With the front encountering such cold air, any precipitation fell as snow.
Snow fell widely across the UK with many areas recording 5 to 15 cm, with 25 cm falling across parts of South Wales.
The closely-spaced isobars indicate strong south-easterly winds, which gave drifting snow in places, further maximising disruption.
A few days before this snow event high pressure had been centred over Scandinavia with cold easterly winds affecting the UK. The night of 4 February 2012 brought a series of weather fronts from the Atlantic.
The cold, dense air was reluctant to move away. The coldest temperatures were across the east of the UK. The precipitation from the weather fronts fell as sleet and then rain across the west of the UK. Further east the precipitation fell as snow and 15 cm fell in parts of Norfolk and Suffolk.
A lot of snow events in the UK are caused by milder air coming up against cold air, some areas get rain and some get snow.
Deciding on the exact boundary between the rain and snow can be difficult.