Relief from the unrelenting heat is finally arriving this week across western Europe, with more unsettled conditions bringing the chance of rain. Temperatures are expected to fall back towards the seasonal norm, with some parts of the UK even falling about 3C below normal by Thursday. After such a scorching summer, and with a temperature drop of more than 15C compared with last Thursday’s heat, it may feel surprisingly chilly.

There are signs that some substantial rain could be on the cards for the south of the UK this week as a cold front moves in from the Atlantic on Monday night into Tuesday. As of Monday, parts of southern England had endured 62 consecutive days of no rainfall – this is observed at a Met Office weather station in Wisley, Surrey. Even the last recorded rainfall here on 16 June amounted to just 0.4mm.

The more interesting weather arrives from Wednesday into the weekend, as low pressure moves across the UK, bringing frequent sharp showers and potentially thundery downpour.

After such a prolonged dry spell, even a few substantial bursts of rain will make a noticeable difference to the environment. Continental Europe is also likely to turn wetter as the main cold front sinks southwards into France and Germany on Wednesday. Farther south however, rainfall is likely to be more hit-and-miss, relying heavily on showers and thunderstorms, with this risk really rising from Thursday.

While the heat is subsiding on this side of the Atlantic, the southern US states have extended extreme heat warnings this week. There is also a significant lack of overnight cooling and relief from the heat, with overnight lows not falling much below 27-28C (low 80sF). For perspective, the UK’s highest overnight minimum during the late-June heatwave reached about 22–23C.

High humidity is also contributing to the uncomfortable conditions and is helping push the heat index to such high levels to warrant the extreme heat warnings. The combination of air temperature and humidity produces the heat index, or apparent temperature, which better reflects how hot conditions feel. Apparent temperatures of 31-33C are being modelled as the overnight lows, with the National Weather Service warnings warning of “dangerously hot conditions” as the forecasted daytime heat index values could exceed 46C, especially across Louisiana and Mississippi.