# Daily mean temperature

Climatological knowledge

Day temperature  T : max / med / min

Air temperature dependent days
• ﻿T max  ≥ 35 ° C
• Desert day
• ﻿T max  ≥ 30 ° C
• Hot day
• ﻿T min ≥ 20 ° C
• Tropical night
• ﻿T max ≥ 25 ° C
• Summer day
• ﻿T med <15 ° C / 12 ° C
• Heating day
• ﻿T med ≥ 5 ° C
• Vegetation day
• ﻿T min <0 ° C
• Frost day
• ﻿T max <0 ° C
• Ice day
not uniformly defined: Cold day
Weather- dependent days
Cloud cover Bright day
Cloud cover Cloudy day
Cloud cover Foggy day
Humidity / temperature Sultry day
Precipitation Precipitation day
Precipitation Rainy day
Precipitation Hail day
Precipitation Snow (cover) day
storm Storm day
storm Thunderstorm day

The average daily temperature , and average daily temperature is in Germany by the German Weather Service since April 1, 2001 by forming the mean value of all measured on the hour air temperature values ( ) 0 through 23:00 UTC (ie from 1 through 12:00 CET ; ) determined : TLTUhrzeit

${\ displaystyle T_ {L} = {\ frac {1} {24}} (T_ {0} + T_ {1} + T_ {2} + T_ {3} + \ dotsb + T_ {23})}$

If values ​​are missing for more than three hours due to a technical failure , the daily mean temperature is alternatively calculated from the temperature values ​​measured at the main synoptic dates 0, 6, 12 and 6 p.m. UTC:

${\ displaystyle T_ {L} = {\ frac {1} {4}} (T_ {0} + T_ {6} + T_ {12} + T_ {18})}$

## Calculation until March 31, 2001

Up to 1900 there were several different calculation rules in the German states and their climate services (Bavarian formula, Saxon formula, etc.; until 1886 also their own Prussian formula, from 1887 conversion to Mannheim formula). From 1901 to March 31, 2001, the daily mean temperature of a location was usually determined from three temperature measurements per day; only the Deutsche Seewarte, based in Hamburg, adhered to its own formula for daily averaging (so-called Seewarten formula) within its area of ​​responsibility until the end of 1935. The times for the manual temperature readings, which were standardized from 1936 onwards, were called Mannheim hours and for many decades were 7, 2 and 9 p.m. local time in German-speaking countries ( + 1 hour each during summer time ). The 9 p.m. value was counted twice and the sum of the four values ​​was divided by 4. The daily mean temperature is calculated using the formula

${\ displaystyle T_ {L} = {\ frac {1} {4}} (T_ {7} + T_ {14} + 2T_ {21})}$

performed. (The times given as T 7 , T 14 and T 21 in the formula correspond here to the times 7, 2 and 9 p.m.) The formula goes back to Kämtz (1831).

Depending on the country, however, there were deviations in the reading dates: For example, the daily mean temperature in the former GDR between 1967 and 1990 was usually calculated from 4 or 8 dates. In 1987, the German Weather Service moved the dates to 6:30 a.m., 1:30 p.m. and 8:30 p.m. world time for practical reasons (from January 1, 1991 also valid for the new federal states) so that all stations have the values ​​at the same time read off. However, the above formula remained valid. While part-time observers with analogue instruments continued to observe on the three dates mentioned per day after April 1, 2001, they have only been used in the full-time monitoring network at DWD climate reference stations manned by specialist staff, where conventional analogue instruments are used to perform manual parallel observations for automated electronic Temperature measurement.

Since this method does not take into account nights with strong cooling too weakly, thermoisopleth diagrams , which show the average daily and annual temperature of a location, were of interest. The data required for this had to be read from analog recording devices before the introduction of automatic measurement systems.

## Examples

 place January July Basel Bern Davos Geneva Jungfraujoch Lugano Magadino Samedan St. Gallen Zurich 0.9 −1.0 −5.3 1.0 −13.6 2.6 0.2 −9.4 −1.1 −0.5 18.5 17.5 11.8 19.3 −1.2 21.1 20.6 11.2 16.2 17.6