Daily weather observations in sixteenth-century Europe

Thirty-two weather diaries written in astronomical calendars in central Eur ope in the late fifteenth and sixteenth centuries are presented and discuss ed. Systematic weather observations were promoted by the rise of planetary astronomy and its application in astro-meteorology. The practice of keeping weather diaries spread from Cracow (Poland) to Ingolstadt (Germany) and fr om there to other universities. The data obtained from these sources provid ed the backbone for setting up series of precipitation indices for Poland, Germany and Switzerland. Monthly statistics of days with precipitation, sno wfall and frost were computed by counting the relevant entries in the most important diaries. The results were compared with either those obtained fro m instrumental measurements in the same place or with those from modern ins trumental measurements in a neighbouring place. The final results show that autumn was considerably colder in the early sixteenth century. April was c onsiderably drier and July was wetter during the period 1508-1531 than duri ng 1901-1960. In order to highlight the impact of weather patterns on grain prices in a year of crisis, the timing of wet and dry spells in southern P oland and southern Germany is compared for the year 1529. Winters became 1. 7 degrees C colder from 1564 to 1576 and the month of July tended to be wet ter than in 1901-1960. Details noted in the diaries kept between 1585 and 1 600 by the astronomers Brahe (near Copenhagen) and Fabricius (in the Ostfri esland region of northwestern Germany) closely agree. It rained more often in June and July and temperatures dropped. The winter months were more freq uently dominated by winds from easterly directions, the frequency of snowfa ll was higher and a deficit occurred in precipitation. This points to a hig her frequency of high pressure in the Fennoscandian area with cold air adve ction from the east or northeast.