Gritting will take place when:
- Roads may be wet and road temperatures are forecast to be at or below freezing.
- Snow is forecast.
- The air is moist and a frost is forecast to form on roads below freezing.
Gritting is usually done before freezing temperatures occur, but falling rain can delay the start. Due to this, roads can freeze until they are gritted.
How the decision is taken
The decision to grit depends on two weather factors:
- the road surface temperature;
- and potential road surface moisture.
Although air temperature may be freezing, it does not mean that the roads will be.
We have a weather station at Pecket Well. This tells us the current state of the road surface along with:
- air temperature;
- wind speed;
- precipitation;
- and other factors.
You may wake up to find frost on your car, but the roads have not been gritted. This is because we decide to grit based on the temperature of roads, not air.
Weather forecasting
We get detailed weather forecasts, daily. These tell us if roads are likely to freeze or if there will be snow. They also tell us the times of day that this could happen. This helps decisions to be made as to if/when gritting will be needed.
We get a 36-hour text forecast daily at 6am, 12noon and 6pm, which gives:
- minimum road surface temperatures;
- predicted surface conditions;
- dew points (at the Pecket Well weather station site).
It includes likely risks and hazards, levels of confidence and snow heights. These initial forecasts are supplemented by updates or further advice as required.
A 5-day forecast is also issued daily. This gives a detailed overview for the next five days, which lets us prepare early for periods of bad weather.
As well as the forecasts, the road network has been thermally mapped. This shows the parts of the roads that are likely to freeze first, in the Borough. These are updated at 6am, 12noon and 6pm and help us to target treatment where it is needed most.
The winter maintenance decision makers review the:
- text forecasts;
- thermal mapping;
- and road surface/weather conditions.
They then decide what part of the network, if any, needs gritting.