A cold snap in Reigate looks to be likely for the weekend: temperatures are due to drop from Wednesday onwards as pressure patterns shift shutting off the balmy warm Atlantic SW airflow we have had since the New Year. A HIGH pressure building to the North combined with a LOW to the South will set up north and easterly winds from the cold continent. In January this could mean snow for SE England and that includes Reigate! The jetstream is shifting to the south of the UK so we will be influenced by Polar air masses for a while. Temperatures will be around 3°C daytime and dropping to around -5°C at night, or even lower in clear skies. Any precipitation could well be sleet or snow and freezing fog is possible in light winds as well (though it actually looks quite breezy so be ready for significant wind chill too!). Not a cataclysmic (Daily Mail style) Arctic blast but a “normal” winter cold snap! There is, however, uncertainty in the models at the moment so keep watching for updates!
The colourful pressure chart above shows pressure patterns for Saturday. The lines show mean sea level pressure (millibars) while the colours indicate pressure in the upper atmosphere at approximately 5000m (note: the colour equates to temperature but do not assume red = warm and blue = cold at the surface, this would not be correct! The blues and greens really show lower pressure at high altitude (500mb = approximately half way up through the atmosphere), while yellows and reds show higher pressure. Forecasting weather using upper atmospheric charts like this one is often used by meteorologists because they show general patterns more accurately than surface pressure charts). The map of the UK shows snow risk for Sunday 13 January.