Anticyclones...

Areas of high atmospheric pressure, ie cold sinking air = little or no cloud forming = little or no precipitation*.

Appear very clear on satellite images... On weather maps, closed isobars which are widely spaced and with a gentle pressure gradient between the centre and edge of the anticyclone... therefore, gentle winds blowing out from the centre (clockwise in N. Hemisphere).

In summer

- Lack of cloud = direct insolation = rapid heating... therefore hot (and dry) weather.
- Lack of cloud = rapid cooling at night... relatively cold ground may cause formation of dew and early morning mist.
- Possibility of sea frets along east coast.
- *Convectional rainstorms may occur in the afternoon.

In winter

- Lack of cloud BUT sun at a low angle in the sky so inefficient heating = remains cold all day.
- Rapid cooling at night = formation of mist, radiation fog and frost.
- Temperature inversions may mean that air pollution is trapped.

Remember, stable and slow-moving systems that may stay in more or less the same place for several weeks. Blocking anticyclones over the British Isles will cause depressions coming in from the Atlantic to move northwards and bypass us.