Yesterday, the Royal Meteorological Institute (RMI) raised its warning for icy roads from code yellow to code orange for the centre of Belgium, including Brussels. Other parts of the country were designated as code yellow.
But what do these ‘codes’ mean in practice?
According to the RMI, the institute broadcasts general warnings several times a day in case of "dangerous phenomenons linked to precipitations, wind, thunderstorms, tides or slippery conditions".
Colour codes, which are defined at European level, reflect the intensity of the weather, based on criteria such as strength of the wind, amount of rainfall, temperature and fog density. They are categorised as follows:
- Code green: Nothing special to report. The forecast weather type doesn't justify issuing a warning.
- Code yellow: Be vigilant. Extreme weather might be possible, but for now just be careful.
- Code orange: Be prepared for extreme weather and follow the instructions on the RMI's website.
- Code red: Extreme weather. Take the necessary measures and strictly follow the instructions of the RMI’s website.
These warnings are used to forecast the weather intensity of each Belgian province and are given by Belgian provinces and for a determined validity period - eg. from 6am to 6pm on a given day.
The thresholds for each RMI warning code are detailed below:
Code yellow criteria
Wind: Wind gusts between 80 and 100 km/h
Rain: 20 to 30 l/m² in 1 hour or 20 to 40 l/m² in 6 hours or 25 to 50 l/m² in 24 hours
Thunderstorms: 20 to 30 l/m² in 1 hour or 20 to 40 l/m² in 6 hours or 25 to 50 l/m² in 24 hours or local strong wind gusts or hailstones of 1 to 2 cm
Slippery conditions: 1 to 5 cm fresh snow in 6 hours or 5 to 10 cm fresh snow in 24 hours or (very) local black ice or (very) local frost or ice patches
Fog: Widespread, visibility < 200 m or locally visibility < 50 m
Code orange criteria
Wind: Wind gusts between 101 and 130 km/h
Rain: 31 to 50 l/m² in 1 hour or 41 to 60 l/m² in 6 hours or 51 to 100 l/m² in 24 hours
Thunderstorms: 31 to 50 l/m² in 1 hour or 41 to 60 l/m² in 6 hours or 51 to 100 l/m² in 24 hours or widespread strong wind gusts or hailstones of 3 to 5 cm
Slippery conditions: 3 to 5 cm fresh snow in 1 hour or 6 to 10 cm fresh snow in 6 hours or 11 to 25 cm fresh snow in 24 hours or widespread black ice or ice patches
Fog: Widespread, thick fog, visibility < 50 m
Code red criteria
Wind: Widespread wind gusts of more than 130 km/h
Rain: Already flooding problems and heavy rain still forecast, or > 50 l/m² in 1 hour or > 60 l/m² in 6 hours or > 100 l/m² in 24 hours
Thunderstorms: Already flooding problems and heavy rain still forecast , or > 50 l/m² in 1 hour* or > 60 l/m² in 6 hours or > 100 l/m² in 24 hours or widespread extreme wind gusts or hailstones > 5 cm
Slippery conditions: Everywhere slippery and fresh snow expected or > 5 cm fresh snow in 1 hour or > 10 cm fresh snow in 6 hours or> 25 cm fresh snow in 24 hours or intense and almost generalised black ice
Fog: Does not apply
The RMI also issues a warning for carbon monoxide intoxication without colour coding when weather conditions impede normal removal of combustion gases from heating plants.
