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April 2021

April 2021

Temperatures (all temperatures in degrees Celsuis; all averages 1991-2020)

Mean daily maximum: 12.1   Difference from average: -0.4

Mean daily minimum: 0.7      Difference from average: -3.3

Mean air temperature: 6.4      Difference from average: -1.9

Absolute maximum: 17.4 (23rd)

Absolute minimum: -3.2 (10th)

Mean grass minimum: -2.5   

Absolute grass minimum: -7.8 (10th)

Mean concrete minimum: 5.0

Absolute concrete minimum: -4.3 (10th)

Number of ground frosts: 22

Number of air frosts: 13

Mean soil temperature at 300 mm depth: 9.6

Mean soil temperature at 1000 mm depth: 8.7

Rainfall (all totals in millimetres; all averages 1981-2010)

Total for the month: 14.4        Difference from average: -36.8

Percentage of the average:  28%

Wettest day: 4.2 (27th)

Number of rain days (>0.1 mm): 8

Number of wet days (=>1.0 mm): 5

3-month total rainfall to 30th April 2021: 118.2          Difference from average: -53.8

6-month total rainfall to 30th April 2021: 395.4          Difference from average: +49.2

12-month total rainfall to 30th April 2021: 816           Difference from average: +167

Sunshine (all totals in hours; all averages 1981-2010)

Estimated total for the month: 229.5              Difference from average: +75.2

[Total for the month measured by the AWS: 185.7]             

Percentage of the average: 149 %

Mean daily sunshine: 7.7       Difference from average: +2.5

Sunniest day: 11.1 (15th)

Number of days with no recorded sunshine: 0

Cumulative sunshine since 1st January: 482.9             Difference from average: +61.1

Note that the monthly sunshine total is now calculated from the UKMO E&NE regional total. Daily sunshine totals quoted here and in the data summary are uncorrected.

Wind (kph; all data from the West Building roof, Lower Mountjoy campus)

Average wind speed: 5.8                               Maximum gust: 67.6 (4th, 16:45, WNW)

Comments on April 2021

April was a dry, sunny but disappointingly cool month, more than a degree colder than March. This is only the 18th time March has been warmer than April in Durham since 1844. This year’s difference of 1.1 °C is the 4th equal largest on record; the last time this happened was in 2012.

Mean air temperature was well below average, the 46th equal lowest for April since 1844. Mean maximum temperature was only just below average but the mean minimum was almost two degrees below average, the 6th lowest value for April since 1844. The absolute minimum on the 10th is the lowest April value since 15th April 2000; no other April nights have been colder this century. The total of 13 air frosts is the 5th equal highest April total since 1844 and the lowest April total since 1956. The total of 22 ground frosts is the 2nd equal largest total since 1874 (with 1887), beaten only in 1922.

Over 80% of the very small precipitation total fell in the last four days, preventing another very dry month like last year. It was nevertheless the 18th driest April since 1850. It was the second sunniest April at Durham since 1882, beaten only in 1914.

It is also notable that there were some very low values of humidity recorded in April, reaching a minimum of 22% at 1500 GMT on the 23rd when light winds (3.2 kph) were from the SSE. Other observers in the NE have already commented on how low some of their humidity readings were in April and this may deserve some further investigation; it is not something I have looked at before in the Durham record. The cause was cold, dry air to start with (low moisture content), aided by anticyclonic subsidence.

Emeritus Professor Tim Burt

Department of Geography

Durham University