Issued: 1630 Tuesday 19th December 2006
Duty forecaster: Simon Keeling
Care whilst driving in the pre-Christmas rush...
I hate fog! I'm sure this is the thought of most of us, especially motorists, and especially at this time of year when so many have to travel to be with loved ones over the festive season.
We don't get the protracted periods of fog that we used to, probably largely due to the clean air act which removed much of the pollution from out atmosphere in the 1950's. You see, for water vapour (an invisible gas) to become visible (condense) the vapour needs something to form on, we call this a nuclei. The more nuclei in the air, the easier it is for the water vapour to condense into the water droplet we see as fog. The dust particles released by factory smoke increased the number of nuclei available and so fog could more readily form. To see more about how fog forms, see our Fog Weatherfacts.
The Clean Air Act was introduced in 1956, but fogs (or smog’s as they became known) continued for a while as people were given time to convert to cleaner fuel. Since this time, smog has become less of a problem, but if we get high pressure forming over the UK during the winter months, fog is bound to form again.
Near Christmas time many of us are travelling and so the pollutants released by car exhaust fumes once again increase the number of nuclei in the air, assisting the development, and more importantly persistence, of fog.
Conditions are ripe over the coming days for widespread, dense, freezing fog, especially across England, Wales, Ireland and southern Scotland. Take care if you are planning on travelling as these conditions could purist up to, and including, Christmas Day.
Whatever the weather, keep the sun shining!
Simon