Our trial data explained - what does this forecast mean?

Date and time

The forecast table gives you an overview of the weather forecast at a specific location, for the next seven days. We provide a long-range 28-day forecast for the UK as a whole. You can find it underneath the forecast table, below the map and flood warnings.

The time displayed in the table shows the forecast data for that specific moment in time, on the hour, for most quantities. For example, a temperature of 10°C shown at 10:00am is the temperature we expect at that moment. The weather symbol, chance of precipitation, and wind gusts are not included in this. These represent the period starting at the time shown, up to the next period. Showers and wind gusts may happen in a location between the hourly times shown. Showing it this way means that they show in the forecast.

Weather symbols

The symbols on the forecast are automatically updated when there is new information available. We use the most recent observation data from across the UK and around the world. This helps to make the forecasts as accurate as possible.

Our 7 day forecast page also has regional information lower down the page. It is helpful to read this along with the forecast.

Chance of precipitation

For example, a 70% chance means a 7 in 10 chance that precipitation will fall at some point during that period.

Precipitation means falling water (rain, sleet, snow, hail or drizzle).

We show the chance that at least 0.1mm of precipitation will fall within 1 hour, on the hourly forecast. Or 0.3mm within 3 hours on the 3 hourly forecast. This precipitation may fall across the whole time or fall in a short sharp burst. The weather symbol can help show the difference between light and heavy precipitation.

Temperature

The number in the coloured bars shows the air temperature at that time. You can select which units to show in Settings (Celsius or Fahrenheit).

Feels like

Feels like temperature takes into account wind speed and humidity. This makes it easier to understand how the temperature will feel.

Temperatures in day tab 

These are the maximum (highest) temperature that is forecast for the day and the minimum (lowest) temperature that is forecast at night. Day is from 9am to 9pm and night is the following 9pm to 9am.

Sometimes the highest temperature for the day will be higher than the temperatures shown in the table. This is because it is the highest temperature forecasted to be reached that day. This may occur between the hourly or three-hourly temperatures shown in the table.

Wind direction and speed

The speed shows the average wind speed expected at that point in time. This is the mean (average) wind speed you may encounter, though in reality the wind will strengthen and lull above and below this value.

The arrow shows the direction that the wind is blowing. The letter shows the direction the wind is blowing from (on a standard 16-point compass rose).

For example, an arrow pointing upwards indicates a wind blowing from the south to the north. The letter S indicates that it is a southerly wind.

NNW would indicate a wind blowing from the north northwest.

The Beaufort scale, is a measure for describing wind intensity. It is based on observed sea conditions, but is also used to describe wind conditions on land.

Wind gust

This value represents the highest wind speed between the time shown and the start of the next period.

Strong winds are shown in bold and represent speeds of 25 knots (or 29 miles per hour) or above.

Visibility

Visibility measures the distance at which an object can be clearly seen.

Humidity 

Humidity is the amount of water vapour in the air. If there is a lot of water vapour, the humidity will be high. The higher the percentage of humidity, the wetter it will feel outside. A value of 100% indicates that the air is saturated and no more water can evaporate into it.

UV

This is an index, developed by the World Health Organisation, called the 'Solar UV Index'. It shows the strength of the sun's ultraviolet (UV) radiation. The index is split into categories (Low, Moderate, High, Very High and Extreme). We have included advice about what you need to do to stay safe in the sun for each category.

UV index	UV summary	Exposure category	Advice
		No significant UV	It's safe to stay outside.
		Low	You can safely stay outside. Consider sunscreen in direct sunlight.
		Moderate	Take care during midday hours and do not spend too much time in the sun unprotected. Sunscreen advised.
		High	Seek shade during midday hours, cover up and wear sunscreen.
		Very high	Avoid being outside or seek shade from 11am to 3pm. Shirt, sunscreen and hat are essential.
		Extreme	Avoid being outside during midday hours. Shirt, sunscreen and hat essential.
		No data

Sunrise/sunset

Sunrise or sunset is the moment when the top of the sun’s orb is level with the horizon. This would be when looking at it from sea level with nothing in the way and with perfect conditions.

We do not use observational data because these results can be affected by:

• how high or low the observer is, compared to sea level
• whether there is something blocking the view of the horizon 
• atmospheric composition, temperature or pressure

We use mathematical equations to work out the time of sunrise and sunset. These equations come from the Global Monitoring Laboratory. This means that you may see this moment at a slightly different time from the forecast.

Air pollution

The air pollution symbol shows the level of air pollution. This can be from pollutants such as sulphur dioxide, nitrogen oxides and particulate matter. This is taken from 'Daily Air Quality Index' defined by Defra, which is shows average concentration of pollution over a period of time. 

The data shows average pollution levels for regions of the country. This means that there may be areas in the region with higher or lower levels of pollution than the average.

If you have a condition that puts you at risk from higher levels of pollution, please see our advice.

Symbol	Category
	No significant pollution
	Low
	Moderate
	High
	Very high
	No data

Pollen

The pollen symbol shows the level of pollen in the air. We measure pollen levels across the country. We also work with other organisations, (like the National Pollen and Aerobiological Unit) to create a five-day forecast.

The pollen count we show is for regions of the country. This means that the pollen count you see on a forecast is for the whole region, not the specific location.

You can get more information about the types of pollen in your region on our pollen forecast page.

Symbol	Category
	No significant pollen
	Low
	Moderate
	High
	Very high
	No data

Pressure symbols

These pressure symbols are not used on our weather forecast table. You can see them on our Surface Pressure Chart page.

If you want to know more, please see our factsheets on air mass and weather charts.

	Cold Front The leading edge of an advancing colder air mass. The front is usually associated with cloud and precipitation, followed by a drop in temperature and/or humidity once it passes.
	Warm Front The leading edge of an advancing warmer air mass. It often brings cloud and precipitation followed by increasing temperature and/or humidity.
	Occluded front (or 'occlusion') Occlusions form when the cold front of a depression catches up with the warm front. It lifts the warm air between the fronts into a narrow wedge above the surface. Occluded fronts bring cloud and precipitation.
	Developing cold/warm front (frontogenesis) This is a front that is forming due to increase in temperature gradient at the surface.
	Weakening cold/warm front (frontolysis) This is a front that is losing its identity, usually due to rising pressure. Cloud and precipitation becomes more fragmented.
	Upper cold/warm front Upper fronts represent the boundaries between air masses at levels above the surface. For instance, the passage of an upper warm front may bring warmer air at an altitude of 10,000 ft, but it wouldn't bring a change of the air mass at the surface.
	Quasi-stationary front A stationary or slow-moving boundary between two air masses. Cloud and precipitation are usually associated.
	Isobars Isobars are lines on a weather map joining together places of equal atmospheric pressure. Air pressure at the surface means the weight of air pushing down. If you move higher (e.g. walk up a mountain) and measure the air pressure, there will be less air above you. This means that there will be less air pushing down, so the pressure will be lower. It is hard to compare it to measurements that are taken at different heights. It is also difficult if we do not know the height that the measurement was taken at. So, we convert all measurements to the pressure they would be if they had been measured at sea level. This measurement is called mean sea level pressure or MSLP. Areas of high pressure are marked with H on the MSLP map. They tend to mean settled conditions. Areas of low pressure are marked with an L on the MSLP map. They tend to mean unsettled and windier conditions.
	Thickness lines Pressure decreases with altitude (height) and is also affected by temperature. As air gets warmer, it expands, or gets thicker if thought of as a layer in the atmosphere. If we measure the height difference between two standard pressure levels, it will tell us the thickness of the air which provides a measure of its temperature. If the air is cold, that height difference will be small. If the height difference is large, the air is warm.
	Trough An elongated area of relatively low surface pressure. The troughs marked on weather charts may also show an area of low thickness (thickness trough). It can also mean a disturbance in the upper troposphere (upper trough). All are linked to increasing cloud and risk of precipitation.
	Convergence line A slow-moving trough, which is often parallel to the isobars and tends to be persistent over many hours. They are quite common in cold northerly outbreaks down the Irish Sea. They affect west Wales, Devon and Cornwall in particular, but can also be in other areas also. This convergence line can mean hours of persistent precipitation over very localised areas. A few miles down the road it is relatively dry, leading to some heavy snowfall/rainfall. In summer the convergence lines are not as easy to forecast. They can still occur due to sea-breeze convergence, and are over the land, whilst in winter they are over the sea.

Learn more about weather conditions and the UK climate with our factsheets.