Many people once again reached for their winter coats and woolly socks at the weekend. This week, though, summer in Germany is set to really gather pace:By midweek a strong early-summer area of high pressure will have established itself over south-western Europe.The decisive factor behind this development is the jet stream, a band of strong winds at an altitude of around nine kilometres, explains meteorologist Martin Puchegger at wetter.com. Over the coming days this jet stream will run well to the north of the high-pressure area, allowing a high to extend from Spain right across into central Europe. At the same time an upper-level low will form over the Bay of Biscay and Brittany, but this will actually help funnel very warm air from southern regions towards Germany.Temperatures set to soar from ThursdayUntil midweek the weather will remain rather changeable.Today and on Wednesday, according to the German Weather Service, we can expect initially unsettled conditions with periods of dense cloud, showers and, especially in the east, some intense thunderstorms. Temperatures will reach highs of between 14 and 22 degrees.From Thursday a heatwave will move in: in the south-west temperatures will climb to as much as 26 degrees. Showers and thunderstorms will still be possible, particularly in the north-eastern half of Germany.Over Pentecost, forecasters are expecting around 30 degrees: the outlook for Saturday, Sunday and Monday is excellent. Weather expert Dominik Jung says: “Widespread highs of 22 to 28 degrees are on the cards. Along the Upper Rhine, in the Rhine-Main region and in places towards Brandenburg, peak values of up to 31 degrees are even possible.”The hottest day is expected to be Whit Monday.From a climatological perspective, 30 degrees at Pentecost is not unusual, but it is far from an everyday occurrence. For the period 1991 to 2020, nationwide maximum temperatures in Germany during the last ten days of May range, depending on the region, between 22 and 26 degrees. A first hot day with temperatures around 30 degrees near Pentecost occurs roughly every three to four years – and thus significantly more often than back in the 1980s.