FLINTSHIRE Council has issued an update on gritting following a night of heavy snowfall.

Roads across the county have been left treacherous after snow fell overnight.

The Met Office has extended the yellow warning for snow and ice in some parts of Flintshire until midday on Wednesday.

READ MORE: Is more snow expected in North Wales today? Find out with hour-by-hour forecast

A Flintshire Council spokesperson said: "We currently have 13 gritters ploughing and salting the county network with assistance from two tractor gritters and five contract ploughs.

"So far more than 315 tonnes of salt has been used with plenty more to come today.

"An additional 20 operatives are hand salting town centres and near sheltered accommodation, and we have two crews dealing with trees and tree branches that have been brought down due to the weight of snow."

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The council decides on which roads to grit in terms of priority. Priority 1 roads are the highest priority main roads. Priority 2 are unclassified roads that form main routes in both urban and rural areas and known problem areas - routes will be treated once the Priority 1 routes are completed and if the council has enough resources. Priority 3 refers to all remaining roads.

The council said the Priority 1 route usually takes three hours to grit. It is 560 kilometres long, which is about 45 per cent of the road network in Flintshire. Once the priority roads are clear, the council moved on to other roads and footways.

In terms of how the gritting process works, salt works by lowering the temperature at which water freezes. It relies on vehicle tyres to spread it over the road and mix the salt in with the snow and ice, so requires traffic to be effective. Salt will work at temperatures down to minus 8 to 10 degrees Celsius. Below that, roads will still freeze.

Rain can wash salt off roads leaving them prone to re-icing. When rain turns to snow coinciding with the rush hour, early gritting cannot take place as it would be washed away and gritters cannot make progress due to traffic congestion.