High pressure has dominated the weather across Aylesbury Vale over the last week.
There has been plenty of dry weather with blues skies and sunshine during the day, but then turning cold overnight with widespread frost in the mornings.
Another interesting feature has been the thick fog during the mornings.
However, not everywhere has seen fog - there have been quite big variations with some areas having thick fog while only a mile or two away there are blue skies.
Fog forms when the water vapour in the air cools sufficiently that it condenses.
It usually needs some kind of dust, salt or air pollutant to be in the air for the water vapour to condense around.
The definition of fog is when visibility is reduced to less than 1km.
Mist is similar to fog, but less dense with visibility reduced to between 1-2km.
There are also different types of fog - for example, radiation fog, advection fog, valley fog and freezing fog.
The Aylesbury Vale is relative flat and surrounded by hills.
In still conditions, cold air tends to sink, which means the air in valleys tend to be colder, and cold enough for the water vapour to condense and form fog.
So over the last week, if you had ventured to high ground such as Coombe Hill and Ivinghoe Beacon, you would have enjoyed bright sunshine while having great views of the fog filling the valley below.
So the reason that, even within a short distance, there was a big variation in the amount of fog recently was mainly due to the changes in altitude.
Looking ahead to this week, high pressure will continue to dominate with plenty of dry and settled weather and the risk of further fog at night.