Was this black Friday for flying due to weather? Hopefully it will start to get better from here on....
I've updated the Wiki with the reality of what happened today, based upon flightradar24.com data as of around 2000 GMT. The data will broadly be accurate, although a few details may be inaccurrate.

Heathrow did the best job of keeping as close as possible to their predicted list of cancellations, but with alomst 200 rotations cancelled there was significant impacts to travel. Most signficant short haul impacts were DUB, EDI, FRA but there were an increased number of long haul cancellations compared to yesterday - as high as 31 including SIN and SFO. BA was responsible for just over half the cancellations at 105 rotations, followed by EI and LH.

199 out of 670 (30%) LHR Departures for 02 Mar - as of 02 Mar 2000 GMT
(was 170 out of 652 (26%) LHR predicted Departures cancellations - as of 01 Mar 2115 GMT)

191 out of 666 LHR (29%) Arrivals cancellations for 02 Mar- as at 2000 GMT
(was 181 out of 652 (27%) LHR predicted Arrivals cancellations - as of 01 Mar 2115 GMT)

Gatwick had to more than double their predicted cancellations during the day, but still managed keep their total cancellations to below 15% of schedule. Here, BA was overtaken by easyJet, Ryanair and AerLingus for the number of flights cancelled and only had to drop 5 flights from the schedule.

55 out of 370 (15%) LGW predicted Departures as of 2000 GMT
(was 20 out of 337 (6%) LGW predicted Departures cancellations - as of 01 Mar 2115 GMT)

52 out of 364 (15%) LGW Arrivals cancelled - as of 2000 GMT
(was 26 out of 354 (6%) LGW predicted Arrivals cancellations - as of 01 Mar 2115 GMT)

London City's schedule was decimated. From a prediction of about 15% of flights being cancelled, that rose to around 70% of rotations not flying. The main destinations affected were DUB, EDI, AMS and ZRH and BA was responsible for just under half of the cancellations followed by Flybe.

105 out of 139 LCY (75%) Departures for 02 Mar - as of 2000 GMT
(was 19 out of 129 (15%) LCY predicted Departures cancellations - as of 01 Mar 2115 GMT)

92 out of 134 (68%) LCY Arrivals cancelled for 02 Mar - as of 2000 GMT
(was 24 out of 135 (18%) LCY predicted Arrivals cancellations - as of 01 Mar 2115 GMT)

I need to defer to others if they wish to keep the Wiki going for the weekend, but hopefully this has been useful to keep tabs on what happened and can be a reference point if/when future Snow and Weather events take place.