Parts of the UK have experienced warm and humid conditions in recent days, with the combination of higher temperatures and moisture making the air feel particularly muggy.
The main reason has been the source and direction of the airflow affecting the country. High pressure to the south of the UK has helped draw warm, moisture-laden air across England and Wales. With relatively high temperatures allowing the atmosphere to contain more water vapour, humidity levels have remained elevated.
However, the weather pattern is now changing. A cold front is moving south-eastwards across the UK, replacing the warm and humid air with a cooler and fresher north-westerly airflow.
Warm air can contain more moisture
Humidity describes the amount of water vapour in the atmosphere. Warm air can contain more water vapour than colder air, provided there is sufficient moisture available. As a result, a spell of warm weather accompanied by an airflow from a moist source can lead to particularly humid conditions.
Recent temperatures have been relatively high across parts of England and Wales. Combined with the moisture in the air, this has produced the muggy conditions experienced at the beginning of the week.
The warmth alone is not responsible. Some very hot regions, such as deserts, have low humidity because little water is available for evaporation. For the UK, the combination of warm air and moisture is what has made the recent conditions feel so humid.
Why can humidity feel uncomfortable?
In warm and humid weather, sweat evaporates from the skin less readily. This limits one of the body’s main cooling mechanisms, meaning conditions can feel warmer and more uncomfortable than the air temperature might suggest.
Relative humidity is commonly used to describe how close the air is to saturation at a given temperature. Because it depends on temperature, the relative humidity can change during the day even if the actual amount of water vapour remains similar.
Dew point can therefore provide another useful indication of how humid the air feels. It is the temperature to which air must cool before it becomes saturated and condensation begins. A higher dew point indicates that more moisture is present in the atmosphere.
READ MORE: Week ahead: Unsettled and fresher weather
A cold front brings a change
The recent spell of humid weather is ending as a cold front moves south-eastwards. The front marks the boundary between the warm, humid air and the cooler, fresher air arriving from the northwest.
As it crosses the country, the front will bring cloud and outbreaks of rain. The rain may briefly become heavier before gradually clearing southeastern areas. Behind it, sunshine and showers will develop, while north-westerly winds introduce air with lower temperatures and reduced humidity.
This change will be noticeable across England and Wales, where temperatures will be several degrees lower. Values are expected to reach 21 to 23°C at best, while northern England, Northern Ireland and central Scotland will generally be in the high teens. Northern Scotland may reach only 14 or 15°C.
Fresher but increasingly changeable
Although conditions will feel fresher, the weather will remain unsettled. Low pressure will frequently influence northern parts of the UK, bringing bands of rain, blustery winds and heavy showers. Some showers could also be thundery.
Temporary ridges of higher pressure may bring shorter periods of drier and brighter weather, particularly across England and Wales. However, further Atlantic weather systems are expected to bring more rain or showers at times.
The key change will be the loss of the warm, humid air that affected the country at the beginning of the week. As cooler north-westerly winds become established, both temperatures and moisture levels will fall, making conditions feel noticeably fresher even between the showers.
READ MORE: Do changing seasons affect the jet stream?
Chief Operational Meteorologist, Andy Page, said: “Many people will have noticed that it has felt unusually muggy recently, even when temperatures haven't been exceptionally high. That's because we've been drawing in a warm, moisture-rich air mass across parts of the UK, particularly England and Wales. Warm air is able to hold more water vapour, so with both warmth and moisture present, humidity levels have been elevated.
“The good news for those who prefer fresher conditions is that a change is now underway. A cold front moving south-eastwards is replacing that warm, humid air with a cooler north-westerly airflow. As this happens, humidity levels will fall and the air will feel noticeably fresher, even if temperatures don't drop dramatically in all areas.
“We'll still see some showers and blustery conditions at times this week, but for many people the lower humidity will make the weather feel much more comfortable than it has over recent days.”
Keep up to date with weather warnings, and you can find the latest forecast on our website, on YouTube, by following us on X and Facebook, as well as on our mobile app which is available for iPhone from the App store and for Android from the Google Play store.
