1 Oct 2013

Potten End Newsletter Article 11

This article originally appeared in the Potten End Newsletter, October 2013.

Potten End Weather

“Don’t knock the weather. If it didn’t change once in a while, 
nine out of ten people couldn’t start a conversation.”
― Kim Hubbard

Weather Fronts

Weather fronts bring a change in the weather and are frequently mentioned in weather forecasts. But what are they?

Weather fronts mark the boundary between two air masses. When the two air masses have different properties; for example, one air mass may be warm and moist while the other might be cold and dry, they produce a reaction in the zone where they meet known as a front.

This reaction is the principal cause of significant weather like showers, thunder showers and related unstable weather. It is caused by air being lifted and condensing in to clouds by the movement of the cold front under the warmer moist air.

The two main types of front are a warm front and a cold front. On weather maps these appear as a line with semi-circles and a line with triangles respectively. The semi-circles and triangles indicate the direction in which the front is moving.

Cold fronts can produce sharper changes in weather and move up to twice as quickly as warm fronts, since cold air is denser than warm air and rapidly replaces the warm air preceding the boundary.

A warm front moves more slowly than the cold front which usually follows because cold air is denser and harder to remove from the Earth’s surface. This also forces temperature differences across warm fronts to be more significant. Rainfall gradually increases as the warm front approaches. Fog can also occur at the head of a warm front.

When a cold front catches up with a warm from, it produces an occluded front. Occluded means hidden. On weather maps this is shown a line with both semicircles and triangles. In an occluded front, warm air is lifted up from the surface, and therefore ‘hidden’. An occluded front can be thought of as having the characteristics of both warm and cold fronts.

In the UK our unique weather is a result of us being an island nation between a large ocean to the west of us, a large land mass to the east of us and our position north of the equator. This means we experience a large number of frontal systems and their associated weather. It is one of the reasons why it is only really possible to forecast up to five days ahead with any degree of confidence.

October Expectations

October is a changeable month weather-wise. In the past, according to our records, we have seen temperatures as high as 25.3ºC (2011) and as low as  -1.7ºC (2008). On average we can expect to see temperatures between 7.5ºC and 15ºC. October can be a wet month with total rainfall between 20mm (2011) and 110mm (2006).