Interesting Word - Heatwave

A heat wave is a prolonged period of excessively hot weather.  In England and Wales, heatwave conditions are reached when the maximum daytime temperature and minimum night-time temperature rise above the threshold for a particular region.

(The length of time spent above the threshold determines the level.

Level 1: Normal summer conditions.
Level 2: 60% or higher risk that the temperature will be above the threshold levels for two days and the intervening night.
Level 3: Temperature above the threshold for the preceding day and night, with a 90% or higher chance that it will stay above the threshold in the following day.
Level 4: Anything above the other three levels.

Each of the first three levels is associated with a particular state of readiness and response by the social and health services, and Level 4 is associated with more widespread response.

The UK is currently set at Level 3.)