Signs of autumn

  • A diagram showing the overhead sun at the equator on Wednesday 23rd September 2015. Photo credit: Przemyslaw Idzkiewicz.

    Minimum temperatures on the night of the 21st of October 2017. Credit: Meteogroup.

    Shallow mist near the Quaggy river. Credit: Meteogroup.

    Shallow mist near Feltham. Credit: Meteogroup.

  • Signs of autumn
    23.09.2017 14:44

    On Friday, the Equinox took place at 20:02 pm. Astronomically the Equinox is the moment in which the plane of Earth’s equator passes through the centre of the Sun’s disk. The equinox marks the point when the duration of day and night is almost equal over the planet. From now until the next equinox in March there will longer periods of darkness over the Northern Hemisphere.

    In parallel, some signs of Autumnal weather were spotted this week with hints of the first overnight frost, mist and fog patches. As an example, once a frontal system cleared during Thursday night the sky cleared across much of the UK. Temperatures dropped away and it was a cold start to the day. The minimum temperatures were -1.2°C in Altnahrra, Sutherland, 1.3°C in Benson, Oxfordshire and 2.9°C in Katesbridge, County Down in Northern Ireland. Another interesting weather element that morning was shallow mist, formed due to an inversion, i.e. an increase in temperature with height, very light winds and a good moisture source. In autumn or winter, a temperature inversion occurs when the air close to the ground is colder than a layer above and this may trap pollutants, there could be mixture of fog and pollution, leading to smog.

    Over the next few days, the UK will be a battlefield between synoptic systems.  An extensive and intense area of high pressure over Scandinavia and a deep area of low pressure to the south of Iceland will bring a moderate southerly airflow across the UK. The Foehn effect will take place in Scotland, keeping relatively mild and dry for the time of the year. However, a change will occur on Wednesday with low pressure systems in the Atlantic pushing in, bringing bands of heavy rain at times, showers and possibly strong south-westerly winds. Temperatures should remain near or slightly above average.

    Looking ahead until the middle of October and having in mind that the medium-range forecast is always difficult, here it is an extended outlook. Especially from the 5th to the 11th of October there is a good deal of uncertainty since currently the mean weather models are struggling to determine the exact track of the ex-hurricane Maria as it moves over mid latitudes. Temperatures should remain near average with northern parts of the UK seeing wetter conditions than the south. From the 12th to the 18th of October, there are no hints for a cold scenario, although a few frosty nights are possible. Normal average precipitation indicated on the medium-range charts means that wet conditions will be mixed with drier interludes. However, there are indications of a risk of one or two strong wind events through this period.

    As we recommend usually, it is better to follow the weather on the daily basis by following us on Twitter, Facebook and our apps to keep up to date.

    By: Mario Cuellar