Я не метеоролог, у них спросите.The definitions meteorologists apply to average and normal temperatures differ in some respects from their everyday meanings. An average temperature is an arithmetical average, but a normal temperature goes beyond that. It is a specific average temperature calculated from a 30-year period, currently 1981-2010. Normals are recalculated every 10 years. Daily highs and lows are averaged, but the results are smoothed so that the average rises and falls by only one degree at a time through the annual cycle of temperatures. In everyday usage, “normal” means “usual” or “ordinary,” but to a meteorologist it’s a specific 30-year average temperature. I occasionally use both meanings.