During winter, snow or ice presence on the road might have serious consequences on road traffic and security and many efforts were done for several years to develop decision-making tools for road management in winter. For this purpose, Météo-France uses, in an operational way a specific system dedicated to the road weatherforecast.
The first one, OPTIMA is a high-frequency (5 min) nowcasting system providing 1 hour forecasting and based on data fusion approach. It is dedicated to real time and short range anticipation of road impacting phenomenon. It was specially developed to work at the road network resolution (5km).
The data OPTIMA uses for the forecast process:
- Radar observation and nowcasting
- Surface observation network and road weather stations observations from customers
- Best available weather forecast (i.e. expertized by human forecasters)
- Specific road weather forecast
As an input for this decision-making tool, Météo-France uses numerical road models, which permit to simulate the behavior of a road under the influence of atmospheric conditions and the behavior of the snow on the road. Since 2012, road models are forced by human expertized atmospheric forecast instead of a direct coupling with numerical weather prediction models. Thissystems, called PEIR (Expertise Predictions for ISBA-Route), are the basis of road conditions forecasting products for French road managers.
Since the beginning of operational road weather forecast in Météo-France, all the products were based on deterministic forecasts, however since 2018/2019 winter, a new approach is tested, based on ensemble forecast.