High Pressure, or to give it its correct title, an anticyclone, generally brings us fine weather. But that is not always the case.

It is formed by air descending through the atmosphere which, as it does, warms up reducing the humidity of the air, thinning out the clouds and often producing sunshine, but it also a bearer of bad tidings for the gardener at this time of the year because it can give damaging night frosts.

There are two types of high pressure that regularly visit our shores, one that is semi-permanent and the other which can move quickly, but give a fine interlude in between two rain bearing weather fronts.

I discussed the formation of the semi-permanent highs in " Weather and The General Wind Circulation " and showed that they were often centred around 30 degrees north. The one which we see most of all is called the " Azores Anticyclone" You will see it on the weather map tantalizingly close and often behind the Weather Presenter.

I have been asked many times why the Weather Presenter hides the high pressure, and my answer is that if they do not move to one side to show you it, then it will have no bearing on the immediate weather.

Sometimes the vertical temperature profile of from the ground upwards around high pressure, shows that as you ascend the air gets warmer, which is the reverse of normal, giving a temperature inversion, so if any cloud is formed by moist air rising up from the surface, it can often get trapped there and spread out to cover the whole sky.

At the surface, the winds around an area of high pressure blow clockwise in the northern hemisphere, and slightly outwards from the centre, so as the High moves across the country the wind direction changes and this is important to decide what type of weather you will get from it.