Bonn · Warm nights and days with record heat: July was the fourth hottest since temperatures have been recorded. Last month, only 18 liters of rain fell per square meter.
Hot days and nights not dipping below 20 degrees Celsius, sun and no rain: July 2018 was the fourth warmest since the beginning of regular weather records in Bonn. There were 62 days with temperatures 25 degrees or higher since April 8, also setting a new record. Each new day of heat adds to that, bringing the record to new highs. A look at data from the Weather Station Endenich at the University of Bonn and the weather history records confirms the weather statistics.
Temperature: With an average temperature of 23.1 degrees Celsius, July was 3.7 degrees warmer than the long-term average. The warmest July was in 2006 with an average of 23.9 degrees, the coolest was in 1907 with 15 degrees. On 29 days, the mercury exceeded the mark of 25 degrees; on 13 days it was more than 30 degrees in the shade. In addition, four tropical nights were counted (in German meteorology it is called a tropical night when temperatures do not drop below 20 degrees Celsius). More summer days (when it is 25 degrees Celsius or more) were last recorded in July 2006. On July 11, Bonn had the lowest temperature of the month at 12.5 degrees. On Thursday of last week, 37.8 degrees Celsius was measured, making it the hottest day of the year so far. That was the third highest July temperature ever measured in Bonn. The highest July temperature recorded is still from the 24th of July 1911 with 38.5 degrees Celsius.
Sun: With the stable high pressure system over Bonn, the sun was able to prevail. With a total of 320 hours of sun, July 2018 finished in second place behind July 2006 (325 hours) and before 1971 (297 hours). July exceeded its monthly target by 117 hours. The sun was out longer than 13 hours on twelve days. Only on one day did the sun appear for less than an hour. In 2018, the hours of sun is already 279 hours longer than the long-term average.
July 2017 was 2.8 degrees cooler than the current July
Precipitation: July was much too dry: Over nine days, we had only 18 liters of precipitation per square meter, which is about a quarter of the long-term average. It also ranks number 165 in the 170-year records measuring precipitation in Bonn. Most of the rain fell on July 21st with six liters per square meter. Two thunderstorms were counted. The scant precipitation meant a dramatic decrease in the level of the Rhine: At the end of the month, the water level of the Rhine in Bonn was 1.34 meters, the lowest since January 31, 2017.
2017 comparison: July 2017 was 2.8 degrees cooler than July 2018. In the previous year, the minimum temperature of 9.8 degrees Celsius was slightly lower, and also the peak of 35.2 degrees was 2.6 degrees lower. In July 2017, there were 12 fewer summer days. There were also two fewer tropical nights. In 2017, precipitation was 119 liters per square meter, which was 101 liters more than this year. The sun was out for 125 hours less than in 2018.
Klaus Kosack was chief statistician of the city of Bonn for decades.
Orig. text: Klaus Kosack. Translation: ck