Abstract: Grain aeration with ambient air is the primary method used in France to maintain grain quality during a long storage period. Its success depends on the number of hours where ambient air is suitable to cool grain. Fan aeration is usually processed in three steps, from the harvest (July) to the early winter (January).Using temperature measurements made on 369 French weather stations between 1997 and 2016, we calculated the number of grain bins where can be properly achieved the three successive temperature targets : 20 °C, 12 °C and 5 °C. We assumed that specific doses were respectively 1000 m3 air/m3 grain for the first aeration stage, 1400 m3 air/m3 grain for the second one and 1800 m3 air/ m3 grain for the third one. Calculations have been made using four specific flow rates (4, 8, 12 et 16 m3/h/m3), assumed to be representative of the equipment in French silos. Results have been mapped by interpolation between the 369 weather stations. Maps reveal that the first temperature target (20 °C) is achieved before the 15/09 everywhere in France including for the lowest specific flow rate, except in the extreme South. For the second and third temperature targets (respectively 12 °C and 5 °C), an East-West gradient is observed. For instance, with a 4 m3/h/m3 flow rate, the 5 °C target can’t be achieved before the 15/01 in a broad area from Brittany to the South-West of France. By contrast, in the North-East area of France cooling grain with ambient air is easier, even with low flow rate.