Heathrow has been one of the most delayed airports in the world for most of Saturday, 7 November, with roughly a third of its departures leaving late as a fog warning that covered London overnight turned into a full day of disruption.
The Met Office issued a yellow fog warning for London and the South East that ran from Friday evening into Saturday morning, saying visibility could fall below 100 metres in places. By midday, flight-tracking data showed about 220 of Heathrow's roughly 610 scheduled departures had already left late, according to aviation site The Contrail, which has been tracking the disruption through the day. Paris Charles de Gaulle has had a similarly rough day, though it is not clear fog is the cause there.
The fog first settled over London overnight into Saturday morning, with the Met Office warning visibility could drop below 100 metres in the worst-affected spots before clearing to mist and haze, the Evening Standard reported. At the time that warning was issued early Saturday, schedules at Heathrow and Gatwick appeared to be running close to normal, but delays built through the day as the knock-on effects of reduced visibility rippled through the schedule.
Fog causes this kind of lasting disruption because air traffic control has to space aircraft further apart on both approach and departure when visibility is poor, cutting the number of landings and take-offs the airport can handle each hour. Even once the fog itself lifts, aircraft and crews that have fallen behind schedule can take hours to catch up, which is why Heathrow's delays built through Saturday rather than clearing with the morning mist.
Forecasters quoted by The Contrail say fog could return to the London area on Saturday evening, which would risk dragging delays into the night and potentially into Sunday's early departures. Heathrow has not reported cancellations tied directly to the fog, and the disruption so far has been measured in delay minutes rather than scrubbed flights.
This follows an earlier Met Office warning for the same fog spell, which this site reported on Saturday morning before the scale of the day's delays was clear.
What this means for your journey: if you are flying from Heathrow today or tonight, check your flight status directly with your airline before leaving, since delays are running well above normal. See our /parking/ guide if you are driving in, or /public-transport/ for Elizabeth line and Underground options if fog is also slowing the roads.