It comes after warm and sunny weather during the Whitsun long weekend, prompting fears that residents would drop their guard and ignore social distancing rules.
Forecasters said Tuesday was set to be the warmest day of the year so far with blue skies almost everywhere.
A meteorologist from the German Weather Service (DWD) said on Monday that the 30C mark could be broken for the first time in 2020.
Across most of the country, high temperatures are expected. However in the east, at the Oder and Neisse rivers, it could become cloudy with some rain or thunderstorms.
The DWD said the chances of the temperature reaching – or even topping – 30C were highest at the Lower Rhine in North Rhine-Westphalia, in the southern Emsland and in Münsterland. About 29C was expected in Cologne, Bonn and Koblenz.
In Berlin and Stuttgart it was set to reach 26C, while the mercury was expected to reach 23C in Munich.
The highest temperature recorded so far this year in Germany was 29C on May 21st and 22nd.
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Weather set to change
People living in Germany should enjoy the warmth while it's here – because on Wednesday things will start to change.
Over the course of the day, it is expected to become increasingly cloudy from the west, and there may also be showers, although the mercury will still hover around 24 to 28C.
On Thursday it will likely get much cooler and humid.
“That's quite a distinctive jump,” said the DWD meteorologist.
According to weather experts, summer officially began on Monday June 1st.
On Friday the DWD presented its preliminary results for spring 2020. According to their report, spring in Germany was one of the sunniest since the beginning of weather records and, as in previous years, quite warm.
At 9.2C, the average temperature was 1.5 degrees above the value for the internationally valid reference period 1961 to 1990.
At the same time, spring was too dry. With around 108 litres of precipitation per square metre, only 50 percent of the long-term average rain fell.