BBC Weather carries National Severe Weather Warnings which are issued by the Met Office. These warning triangles appear in our national and local weather broadcasts when extreme weather conditions are forecast.
The warnings are colour-coded, with the colours reflecting the likely impact of the predicted weather.
A yellow warning is the lowest level, rising in severity through amber to red for the most severe weather.
You would probably see a red triangle used two or three times a year, whereas yellow triangles could appear several times in the space of a week.
Forecasters need to look at two things when issuing a weather warning. How severe will the weather be and how confident are they that it will happen? Plug this into a grid and you come up with the level of warning. Let's have a look at a couple of examples.
Light snow, confident forecast
In this scenario, there is a confident forecast of light snow showers so it is very likely that snow will fall, but the amounts of snow are expected to be small so the impact should be fairly low.
A yellow warning is issued, which would only go up to amber if the forecast changed to heavier snow.
Heavy snow, high level of uncertainty
In an alternative scenario, a weather front pushing in from the west is expected to produce rain, but there is a risk of this turning to heavy snow at some point as it meets colder air.
The potential impact of the snow is fairly high, but there is also a high degree of uncertainty in the forecast so initially a yellow warning is issued. This could move up to amber nearer the time as confidence in the forecast increased.
So whenever you see the warning triangles appearing on our broadcasts it is worth not just taking an extra interest in the forecast, but also looking out for updates as the warning level could change.