IT only appears at certain times of the year and is often associated with snow, but it is not Santa Claus.

Rather, it’s the Pembrokeshire Dangler and this is the reason that the Met Office has issued a yellow weather warning for Snow and Ice.

The Met Office weather warning reads: “Wintry showers will feed southwards across southwest Wales and parts of Devon and Cornwall through Wednesday and Thursday, moving well inland on brisk northerly winds. Some snow accumulations will be possible in places, especially overnight and/or farther inland away from the immediate windward coast.

“Whilst some places will see little or no lying snow, where showers are most frequent accumulations of 2-5 cm are possible, and perhaps up to 10 cm in a few isolated spots, more especially on hills above 200 m elevation in Pembrokeshire and west Carmarthenshire.Gusty winds and hail may accompany some of the showers, and where showers persist and/or snow partially thaws and refreezes overnight, this will bring a risk of ice.”

The Pembrokeshire Dangler is a weather pattern that creates a line of showers running north to south across the Irish Sea. It often brings snow in late autumn and winter, when the sea is still warm but very cold Arctic air moves in overhead.

It forms when northerly winds are squeezed between the Rhins of Galloway and the Antrim Plateau. Local land breezes then strengthen the effect, causing winds from both sides of the Irish Sea to meet. This meeting point sets up a line of rising air that creates strong, repeated showers. As these showers pass over warmer water, they grow even more, leading to long-lasting downpours or snowfall over Pembrokeshire, as well as parts of Cornwall and west Devon.

On November 25, 2005, the Pembrokeshire Dangler gave 20 centimetres (7.9 inches) of snow across Bodmin Moor and across parts of northwest Devon, particularly around Barnstaple, causing considerable disruption.

Exactly five years later on November 25 2010 another Pembrokeshire Dangler event caused three to four centimetres (1.2–1.6 inches) of snow in the Bodmin area.

Afternoon: Rain.

Evening: Wintry showers.

Overnight: Sleet showers with snow in parts of Cornwall possible, particularly on higher ground.