Horses graze in a paddock with fog enveloping the trees behind them, near Leith Hill in Surrey, south west of London, Monday, January 23, 2017. Thick fog has caused numerous flight delays and cancellations at London Heathrow and other area airports. The Met Office issued a severe weather warning for London and most of southern England as driving conditions were also hazardous and slippery. (Photo by Matt Dunham/AP Photo)
