 The temperature starts to rise markedly in April, highs usually reach the 25 °C mark at the end of the month, though short cold spells with lows in the 0–5 °C zone and ground frost may strike even in mid-May.In the summer, prolonged heat waves with highs between 32–35 °C interchange with short cooler and wet periods following cold fronts from the West with highs between 18–25 °C.Humidity is usually low in the summer, but may rise during more unsettled weather.