The answer is, when it only lasts two days as it's recently done in the UK.

If this was 'Play your cards right' and this was Bruce Forsyth he would very likely being saying: 'You don't get anything for a pair - not in this game'!

Yes, the 1st of July was a hot day at Heathrow and broke the record for the hottest July day in the UK, but one hot day doesn't a heat wave make, you need that to happen for at least five consecutive with maximum temperature 5°C higher that the long-term average.

https://xmetman.wordpress.com/2015/0...t-a-heat-wave/