The UK is currently under the influence of high pressure, and has been for some days.
But what actually is high pressure and how does it form? The mass of the Earth’s atmosphere causes a pressure to be exerted on the surface, and is measured in units called hectoPascals (shortened to hPa). You may have seen “isobars” on a TV weather map.
These lines represent areas of equal pressure.
The standard pressure at sea level is 1013hPa, but this is not uniform across the planet, and is affected by the ascent and descent of air. When air cools, it becomes denser and begins to descend.
The descending air puts more pressure on the surface below, therefore giving areas of high pressure.
These regions of high pressure are also known as anticyclones, and generally bring dry and settled weather with light winds.
These winds circulate clockwise around the centre of an anticyclone in the northern hemisphere and anticlockwise in the southern hemisphere.
Often it also brings sunny spells, with frosts at night in the winter. However, in some cases it can bring overcast conditions, which can persist for days on end with the high pressure acting like a lid, preventing cloud from dispersing.
This is colloquially known as “anticyclonic gloom”.
Conversely, areas of low pressure (also known as depressions) are formed by air that is ascending.
The rising air causes less pressure to be put on the surface.
The rising nature of the air also causes it to condense into clouds, often bringing rain (or potentially sleet and snow when cold enough).
As a result, areas of low pressure tend to be associated with wet and windy conditions, with the winds circulating anti-clockwise around depressions in the northern hemisphere. In Aylesbury Vale it’s looking likely that we will remain under the influence of high pressure for the next couple of days keeping it dry with some sunny spells.
As we head towards the weekend, there are suggestions low pressure could start to take a foothold with spells of rain at times.
However, it looks relatively mild with wintry weather being kept at bay, although there remains the risk of the odd frost.