Weather Warnings

BBC Broadcast Meteorologists take care to prepare us, but not scare us, with three levels of weather warnings.

The first indication that bad weather is approaching can be given with a 'Weather Watch' which would suggest a 20 - 40 % chance of bad weather.

The next indication that bad weather is approaching can be given with an 'Early Warning'. This will be broadcast on the website, digital text services and Ceefax. This could be issued up to five days in advance and will emphasise that while these conditions are possible, they're not certain.

Before the second stage 'Weather Warning', indicated by the red warning symbol, is broadcast on all BBC Weather output, forecasters at the Met Office and the BBC have to be sure that the gales, snow, rain or fog have reached the following criteria:

Gales
Severe gales - gusts of 70mph (60 knots) or more.
Severe gales/storms - gusts of 80mph (70 knots) or more.

Snow
Snow falling at a rate of approx. 2 cm/hr or more expected for at least two hours.

Blizzards/drifting - moderate or heavy snow with winds of 30mph (25 knots) or more with visibility reduced to 200 or less, or drifting snow giving similar conditions. Blizzards are severe when visibility is reduced to near zero.

Very heavy snowfall, blizzards or drifting - expected to give depths of 30cm or more causing widespread disruption in communications.

Heavy rain
Expected to persist for at least two hours and to give at least 15mm within a three hour period.

Dense fog
Visibility generally less than 50m.

Heatwaves
Day and night temperatures which prompt heatwave warnings can vary across the UK, however, when there is an 80% chance of extremely high temperatures on at least two consecutive days, then a heatwave warning is issued, along with NHS contact details for further information. More on the effects of heat.

Glazed frost/widespread icy roads.
Generally occurs when rain freezes on contact with road surfaces.

Any BBC Weather Centre 'Early Warning' is based on an 'Early Warning' received from the Met Office. These are issued when there is an overall risk of disruption to 60% or more of the population, somewhere in the UK.

It is also the Met Office's responsibility to filter information down to the emergency services, local authorities and some government departments too. If conditions worsen and start to match the list above, this is stepped up to a 'National Severe Weather Warning'.

The Environment Agency uses a three-tiered warning system to tell the public about the risk from flooding. More on Flood Warnings.