About forecasts on the website and app

8th November 2019 Last updated at 15:42

General information

Last updated: Forecasts are updated as often as hourly. The time each forecast was last updated is displayed, where appropriate.

Actual forecast location: When you search for a location or UK postcode we provide the most meteorologically appropriate forecast. In most cases it will be the closest geographical point, but sometimes the nearest forecast isn't the most accurate if you are searching for a coastal location or one at high altitude. In these instances we provide the most suitable alternative.

Daily forecast

Symbols indicate the predominant weather for the day or night in question, calculated based on a weighting of different types of weather. So if a day is forecast to be sunny with the possibility of a brief shower, then we will see a sunny or partly cloudy symbol rather than a rain cloud. For the purposes of this forecast, 'day' runs from 0600 to 1800 and 'night' from 1800 to 0600.

The maximum temperature is the highest temperature forecast between dawn and dusk, and the minimum temperature is the lowest temperature expected from dusk on the day in question to dawn the next day. You can toggle between Celsius and Fahrenheit from within Settings.

Wind speed and direction

The daily wind speed value is the maximum expected over the course of the day (or night, depending on the time you're viewing the forecast).

Wind direction is based on a 16-point compass: W, SW, SSW, etc. The wind arrow shows the direction in which the wind is blowing.

You can toggle between mph and km/h from within Settings.

Sunrise and sunset indicate when the upper limb of the Sun appears, as refracted by the atmosphere, to be on the horizon.

Hourly forecast

Symbols indicate the weather for the stated time.

Temperatures are forecast for the stated time. You can toggle between Celsius and Fahrenheit from within Settings.

Wind speed and direction are the conditions expected at the time given.

Wind direction is based on a 16-point compass: W, SW, SSW, etc. The wind arrow shows the direction in which the wind is blowing.

You can toggle between mph and km/h from within Settings.

Humidity indicates how much water vapour the air contains compared to the maximum it could contain at that temperature.

Pressure is measured in millibars (mb).

Visibility is based on whether the human eye can see the following distances:

  • Very poor - less than 1km
  • Poor - between 1km and 4km
  • Moderate - between 4km and 10km
  • Good - between 10km and 20km
  • Very good - between 20km and 40km
  • Excellent - more than 40km

Environmental summary

All indices are available for UK locations, and the UV index is also available for some international locations.

UV index

The UV index shows the risk level posed by ultraviolet radiation from the Sun. The risk from UV is greatest when the Sun reaches its highest point in the sky around midday. Thick cloud can greatly reduce UV levels but certain types of thin cloud, surprisingly, can magnify the effect. Points on the index are Low, Moderate, High, Very High, and Extreme.

Pollen index

The pollen index, available from March to September, shows the risk from tree, grass and weed pollen, and fungal spores. Points on the index are Low, Moderate, High, and Very High.

Air pollution index

The air pollution index uses a complex chemistry model to produce a forecast for five main pollutants: sulphur dioxide, carbon monoxide, nitrogen dioxide, ozone and PM10 (particulate matter of less than 10 micrometres). The index shows the combined risk from these pollutants. Points on the index are Low, Moderate, High, and Very High.

Maps

Time

The time shown on the map is local to the selected location.

What do the maps show?

We have a combination of satellite and radar images for observed charts, and rain, cloud, snow and fog for forecast charts. The charts show 12 hours of weather prior to the current time and also the weather to be expected for the next week.

What is the difference between a forecast chart and an observations chart?

The forecast chart shows the expected conditions at the time shown. Blue areas represent rain, white areas show snow, and grey areas are cloud.

The observation maps tell you about weather that has already happened. Radar is used to detect where there is moisture in the atmosphere (which could be rain, snow, hail and very occasionally a large cumulonimbus cloud). The 'echoes' received by the radar are shown on the 'observation' charts.

This gives an excellent indication of where rain (or snow or hail) is falling at a given time. The brighter the colours, the heavier the rainfall. This data is quality controlled, however there are some circumstances where the radar may indicate that rain is falling, but it may be drying up before it reaches the ground, and very occasionally it may still show a very large moist cloud!

What do 'pressure charts' show?

The white lines on the charts (isobars) join together places of equal pressure. The isobars are shown at intervals of 4 millibars. 'LOW' and 'HIGH' might be written at the centre of areas of low and high pressure.

The forecast information you see on our weather maps is updated regularly. Quality control of the data is carried out by the duty forecaster at BBC Weather Centre. Any changes made are sent to all of our outputs, so the data you see on the website is the same as that you see on TV.

Observations

Observations are recorded as often as hourly. The time of the observation is displayed beside the data.

Observations are made on the hour, so the weather information (including temperature, wind speed and direction, humidity, visibility and pressure) reflects the conditions at that time. For more information about these values, please refer to the Hourly Forecast section above.

Coast and Sea

Coastal Forecast

This is a Met Office commissioned weather forecast for the inshore waters around the UK coast.

Detailed weather and sea state forecasts, for the next 24 hours in 4 time periods, are available for 24 sailing areas around the coast.

The data is sourced from the Met Office Mesoscale model and the UK Water Model.

The file is updated twice daily at 0500 and 1700. The figure in millibars for pressure is followed by R (Rising), F (Falling) or S (Steady).

Shipping Forecast

Overview

This file is updated 4 times a day at or after approximately 0015, 0505, 1130 and 1725.

It gives a summary of gale warnings in force, a general synopsis and area forecasts for specified sea areas around the UK.

Area Forecast

Area forecasts for the waters around the United Kingdom are disseminated via NAVTEX transmitters at Cullercoats, Niton and Portpatrick and we publish these here.

They are broadcast (and published on our site) at approximately 0620/1820 (Portpatrick), 0840/2040 (Niton) and 0900/2100 (Cullercoats). These give a summary of gale warnings in force, a general synopsis and 24 hour forecasts plus and outlook for the following 24 hours.

Extended Outlook

Once a day an Extended Outlook is broadcast via each of the UK NAVTEX stations on 518 kHz. The extended outlook aims to signpost expected hazards for the Cullercoats, Niton and Portpatrick areas during a three-day outlook period beyond the period of the 24 hour forecast. We publish this file at 2200 each day.

High Seas Forecast

We publish at 0800 and 2000 GMT the text of these forecasts for the high seas Met Area 1 which are broadcast by the GMDSS Inmarsat EGC SafetyNET service twice a day at 0930 and 2130 GMT.

The bulletin is in three parts: storm warnings, general synopsis and forecasts for the sea areas. Storm warnings are broadcast at other times when necessary but these are not currently published on our site.

Warnings

We currently publish ad-hoc Coast and Sea warnings and their associated cancellation messages as soon as we receive them.

Previous gale or other warnings for other areas may still be in force. Old cancellations will only be over-copied when a new file arrives and a blank space will be left if we have received nothing.

Please always refer to the latest Shipping and Inshore Waters forecast, or other sources, including Coast Radio, NAVTEX and Coastguards, for more complete information.

In the Shipping Forecast, Gale Warnings (Force 8 and above) are issued whenever mean wind speeds are expected to reach or exceed 34 knots (Force 8), or gusts (other than in isolated thunderstorms) are expected to reach or exceed 43 knots.

Strong Wind Warnings (Force 6 and above) are issued when required for the Inshore Waters of the UK.

In the forecasts for the High Seas of the North Atlantic, Storm Warnings are issued when the mean wind speed is expected to reach or exceed 48 knots (Force 10 or above). These are not currently published on our site.