Weather forecastingWe use regular and detailed weather reports to help us make decisions on where and when to grit roads during periods of severe winter weather.
Severe winter weather is defined as when a severe weather warning has been issued by the Met Office. These are issued when the probability of a specified event occurring exceeds a pre-defined threshold, for example, if there is greater than 60 per cent probability of snow falling at a rate of more than two cm per hour for more than two hours.
It is the road surface temperature and whether the road is wet or dry that determines the course of action taken, rather than the air temperature.
Delivery of the winter service therefore depends on the receipt of accurate forecasts of road surface temperature and state, together with humidity which is critical when conditions are marginal i.e. when temperatures are close to zero.
Derbyshire has a significant proportion of marginal nights in a winter season therefore our local knowledge and expertise is vital in deciding what to do.
Our engineers have electronic access to real time weather data. They can view the forecasts for each geographical domain and the associated thermal mapping information, which gives the variation in predicted road surface temperature and condition (frost, ice, snow etc) across the county.
Road weather station data can also be viewed giving actual real time information on weather, road surface temperature, road wetness and salt concentration 24 hours a day.
Access is also available to Met Office weather which shows the type and intensity of precipitation. These facilities allow our engineers to make appropriate and timely decisions.