# Annual Summary 2021

**The weather at Durham in 2021**

In terms of temperature, **January** 2021 was quite the opposite to January 2020, which was the 5th warmest January on record. January 2021 was the 34th equal coldest January since 1850, the coldest January since 2010. It was the 54th equal lowest mean maximum and the 44th equal lowest mean minimum. There were no ‘ice days’, the lowest maximum being 1.1 °C on the 8th. Apart from a 5-day dry spell (22nd – 26th), the high frequency of rain days continued from December throughout January; altogether there were 22 rain days and 18 wet days. The wettest day was the 20th, the third day to be affected by Storm Christoph which provided 38 mm in total. This was the second wettest January on record at Durham since 1850; only January 1948 had been wetter (192.1 mm). Despite all the rain, the number of sunshine hours was just about average.

The mean air temperature for **February** was the 114th equal highest since 1844, below the 1991-2020 average but still in the third quartile of all winters since 1850. It was the 18th wettest February since 1850 but nevertheless drier than February 2020 (87.2 mm in 2020). Sunshine was a little below average, perhaps a surprise given it was quite a wet month. The first half of the month was dominated by easterly winds and there was some very cold weather in the middle of the month, with one ice day and an absolute minimum of -9.4 °C on the 12th. Mild spring-like weather towards the end of the month saw an absolute maximum of 14.5 °C on the 27th.

The mean air temperature for **winter** as a whole was 3.7 C, 0.6 °C below average, the 94th equal coldest on record since 1844. If it seemed unusual, it was in fact only the coldest winter since 2018. Most significantly, it was the wettest winter on record since 1850 (328 mm), beating the previous record from 1854. There were 188 hours of bright sunshine, just 9 hours below the winter average, almost into the upper quartile for winter totals since 1883.

Two very warm days at the end of the month (30th: 17.1 ˚C; 31st: 20.8 ˚C) helped raise the mean air temperature in **March** to 7.5 ˚C, the 9th equal warmest at Durham since 1844. The maximum on the 31st is the 7th highest March maximum on record. Durham’s warmest ever March day was 28th March 2012: 21.8 ˚C. The number of air frosts was relatively low (4); only 13 Marches have had a lower total since 1900. There was the second equal lowest total of ground frosts (6, with 1938), beaten only in 1960 (3). It was a dry month, with only just over half the average amount; the wettest day received only 7.6 mm. This was the 43rd driest March at Durham since 1850. Despite the low rainfall total, the number of rain days was exactly average. Given the relatively high number of rain days, sunshine was, not surprisingly, just below average, reflecting often cloudy conditions.

**April** was a dry, sunny but disappointingly cool month, more than a degree colder than March. This is only the 19th 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 a bigger difference 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, and the lowest since 1956. 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. April 1st was exactly 13 degrees colder than the day before in terms of maximum temperature! Over 80% of the very small precipitation total fell in the last four days, preventing another very dry month like April 2020. It was nevertheless the 18th driest April since 1850. There was no measurable rainfall between the 13th and the 26th. 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 commented on how low some of their humidity readings were in April 2021 and this may deserve some further investigation. The cause was cold, dry air to start with (low moisture content), aided by anticyclonic subsidence. The average humidity for the month was 69%.

**May** was a cool, wet month. Mean air temperature was equal 72nd lowest since 1844 (n = 178), the coldest since 1996. The mean maximum was also the coldest since 1996, equal 82nd lowest since 1844. There was the lowest mean minimum since 1996, the equal 61st coolest since 1844. There was the highest number of ground frosts in May since 2013. In the end, there were three days at 20 °C or above; just over a quarter of Mays (51) have more days above 20 °C than this, so in the end a total of three is not that unusual. However, there were no days with a maximum above 21 °C; 98 Mays (just over half) have had at least one day above 21 °C since 1844. It was the 21st wettest May on record since 1850, the wettest May since 2013. The 12-month total is the 47th highest for any 12 months on record (n=2046), just outside the top 2% of totals. It has been a very wet ‘year’ therefore, notwithstanding a dry March and April. The sunshine total was 53rd lowest since 1882, the lowest May total since 2007. Even so, there was 85% of normal, perhaps surprising given the high rainfall.

**Spring** had a mean air temperature of 7.8 °C (0.7 °C below average), equal 120th warmest since 1844, the coolest spring since 2013. The mean grass minimum was also the lowest (-0.4 °C) since 2013, equal 59th lowest since 1874. There were 28 ground frosts but this is only the equal 89th highest spring total since 1874. After the driest spring on record in 2020, this spring was close to average (125 mm): a combination of very dry March and April and a very wet May. There were 501 hours of bright sunshine; the estimated total is surprisingly high, ranking 13th highest since 1882, no doubt helped by an exceptional April.

**June** was a warm month, with the 11th highest mean air temperature since 1844. The mean maximum air temperature is the 12th equal highest since 1844. This was despite a few cool days, with a maximum of only 12.6 °C on the 25th, the 400th coldest June day since 1844 (n=5305 – some gaps plus no data for June 1847), so within the lowest 8%. The coldest June day on record at Durham is 2nd June 1953, Queen Elizabeth’s coronation day when the maximum only reached 7.2 °C. The mean minimum for June 2021 is the 8th equal highest on record since 1844. No rain was recorded for the first 19 days. There were only 5 rain days in all but the total of 16.2 mm on the 24th ensured that it was not a record-breaking month. In the end, the total of 28.8 mm is only the 40th lowest June total since 1850. The driest June on record at Durham is 1925 with only 1.7 mm recorded. Given a dry month, sunshine was above average, although not by a great amount; it is the 96th highest total in 139 years since 1882 (no data for 1884).

**July** was a warm month, mainly because night-time temperatures were unusually high; daytime temperatures were less extreme but still very good in comparison to many previous Julys. The mean maximum is the 14th equal highest on record since 1843, whereas the mean minimum is the 4th equal highest; mean air temperature is the 6th equal highest on record. There were four days with maxima above 25 °C, two more than average but not an exceptional total. The absolute maximum of 28.5 °C is the 27th hottest July day in Durham since 1843. There were 21 days with maxima above 20 °C, five more than average, but again not an exceptional total. The absolute minimum for this July has only been exceeded four times; if we exclude 1846, 1853 and 1855 when the thermometer was unscreened, then only the record holder 1983 has seen a higher July absolute minimum (9.3 °C). The mean grass minimum is the 4th highest since 1874 (with 1945 and 2018), beaten only by 1926 (11.5 °C) and by 2005 and 2019 (both 11.6 °C). As expected there were no ground frosts; the last July ground frost in Durham was in 1940. Rainfall was a little above average, the 106th highest July total in 172 years; this was so even with no rain at all recorded between the 13th and 26th inclusive. Sunshine too was very close to average.

Mean air temperature in **August** was just below the 1991-2020 average, with the mean minimum just above average and mean maximum just below. The mean air temperature is the 42nd highest for August since 1843 (n=179) so just inside the upper quartile overall, if a little disappointing by modern standards. There were no days above 25 °C, something that has happened in 101 Augusts since 1850. The total of days above 20° C (16) is the 31st equal highest total. There were four days with maximum temperature below 16 °C, but 74 Augusts have had a higher number, so not an unusual month, if disappointingly chilly in cool winds from the north-east quadrant in the second half of the month. This was the driest August since 2008, the same total this year as in 2009. Despite this, the number of rain days was a little above average; this is the 19th equal highest August total, but there were concerns that the tipping bucket raingauge was overestimating rainfall totals for some reason. August was a dull month, the 26th dullest since 1880, 46 hours less than average (equivalent to 1.5 hours per day).

For **summer** as a whole, the mean air temperature was 15.8 °C, 0.9 °C above average, the 9th warmest summer at Durham since 1844. Four summers have been warmer at Durham this century: 2018, 2003, 2006 and 2013. Both June (11th warmest) and July (6th warmest) were very warm months; August was relatively disappointing by comparison. Both mean maximum and mean minimum for summer 2021 were 0.9 °C above average. The mean maximum (20.2 °C) is the 16th equal highest on record, whilst the mean minimum (11.5 °C) is the fifth highest on record. Summer rainfall (142.6 mm) was just 75% of the average amount. Sunshine hours (490) were 19 hours below average. For the Davis Index of summer weather, this was the 26th best summer since 1900 Index value = 750), so just into the upper quartile.

**September** was the second warmest in the Durham record since 1843 (15.5 °C), surpassed only in 2006 (15.9 C). By 0.05 °C, September was warmer than August, only the sixth time this has happened, and again the first time since 2006. The mean maximum is the third highest on record (behind 1865 and 2006) and the mean minimum is the second highest on record, again behind 2006. The 8th saw the third hottest September day on record (28.0 °C), exceeded only by the first two September days in 1906 (30 °C and 29.3 °C respectively), while the 7th (27.2° C) is the equal sixth warmest September day on record (n=5360). The minima of 15.2 °C on the 10th and 11th are the 28th equal highest September minima on record. Rainfall was three quarters of normal, almost the same total as for August. There were fewer rain days and wet days than usual. Just three days recorded substantial totals: 10th (9.6 mm), 14th (12.8 mm) and 26th (9.2 mm). Sunshine was almost exactly average for September. Other than the brief heatwave on the 7th/8th, perhaps the most notable weather event was the passage of a very active cold front on the morning of the 27th. Air temperature fell from 16.5 °C at 0700 GMT to 9.7 °C by 0900; altogether 12.6 mm rain fell in 4 hours (between 0700 and 1100 GMT), with 5.6 mm in the first hour (0700-0800).

**October** was a mild month with mean air temperature more than a degree Celsius above average, the 15th warmest on record since 1843. The mean maximum was the equal 12th warmest since 1850, with the mean minimum 11th warmest on record. The absolute maximum of 20.9 °C on the 7th is the equal 24th warmest October day since 1900 (n=3782), the first of two remarkably mild October days with a maximum of 20.4 °C on the 8th (=35th warmest). The minimum of 14.7 °C on the 8th is the 6th warmest October night on record. This was the 40th wettest October since 1850, just into the upper quartile. The wettest ‘day’ was the 5th when 26.8 mm was recorded in the 24 hours ending 0900 on the 6th (By convention the total is ‘thrown back’ to the day before.). The ‘day’ before received 15 mm, with rain starting in the hour after midnight, continuing through to 2300, a combined total in the ‘clock day’ of the 5th of 41.8 mm therefore, equivalent to the 4th wettest October day on record. Not surprisingly, sunshine was slightly below average. There was a gust of 74 kph on the 27th at 02:15 with the wind blowing from the west.

This was the 6th warmest **November** at Durham since 1843. For most of the month, it looked like ranking even higher, but a couple of quite cold days near the end of the month, following the passage of Strom Arwen, brought the average down. The maximum of 2.55 °C on the 28th is the 85th lowest November maximum since 1900 (n = 3660). The mean maximum was the equal 7th highest on record, and the mean minimum was the equal 13th highest. There were only 5 ground frosts, the equal 6th lowest total since 1874, but one more than last year. The number of air frosts (3) is the equal 25th lowest total, again one more than in November 2020. The total rainfall of 51 mm is the 64th lowest total since 1850. It would have been a much drier month but for Storm Arwen: 26.4 mm was recorded on the 26th; most of the rain fell between 2000 on the 26th and 0400 on the 27th. The number of rain days (14) was relatively low: the equal 35th lowest total on record. Given the relatively low number of rain days, it is not surprising that sunshine was a little above average, the 20th sunniest November since 1881. The maximum gust associated with Storm Arwen was at 01:15 on the 27th: 90.1 kph with winds from the NE. The passage of the cold front saw a drop in temperature from 4.9 °C at 0:06 to 0.6 °C at 00:50.

**Autumn** was the 2nd mildest on record since 1843 at Durham (11.6 °C, 1.6 °C above average), exceeded only in 2006 (12.0 °C). The mean maximum (15.0 C) was also the 2nd highest on record, while the mean minimum was the equal 2nd highest on record (8.1 °C, with 1857 and 2011); in both cases, 2006 again holds the record. There was the equal 11th lowest total of air frosts (3); only autumn 1984 has recorded no air frosts since 1850. There was the equal second lowest number of ground frosts (6, with 1984); only autumn 2011 has had fewer (4). Autumn rainfall (183.4 mm) was 94% of average, ranking 96th in a series of 172 years since 1850. However, there were relatively few rain days (44, equal 43rd since 1868) and wet days (1 mm or above: 26, equal 29th since 1868). The autumn sunshine total (305.3 hours, 102% of average) is just into the upper quartile for sunshine data since 1880, ranking 106th in a series of 142 years.

**December** was a little milder than normal, night-time temperatures the more so. The mean air temperature (4.8 °C) is equal 129th highest on record in the 179 Decembers since 1843. The mean minimum is equal 121st highest and the mean minimum is 126th highest. Whilst temperatures stayed close to average for much of the month, there were some milder days in the middle of the month and three very mild days at the end. The 30th was the 30th equal warmest December day since 1843 whilst the 31st (maximum 13.7 °C) is the warmest New Year’s Eve on record at Durham. The minimum temperature on the 31st (11.0 C) is the 6th equal warmest December night on record. There were fewer air frosts than normal, only 4, the 11th equal lowest total since 1900. There were 12 ground frosts, the 12th equal lowest total since 1874. Rainfall was just a little above average, but it was a dull month, the 41st lowest total since 1880 (n=140), just into the second quartile.

For the **year** as a whole, mean air temperature was 9.8 °C, 0.4 °C above the 1991-2020 average, the 14th warmest year on record since 1844. The mean maximum temperature was 13.6 °C, equal 13th warmest since 1844, whilst the mean minimum was 5.9 °C, equal 14th warmest. The annual precipitation total (734.4 mm) is the equal 42nd wettest, with 2019, the wettest years since 2013. There were no very wet days, the wettest being 26.8 mm on 5th October, the equal 52nd lowest annual maximum since 1850. Total sunshine hours for the year were very close to average (1473.9 hours).

**Emeritus Professor Tim Burt**

Department of Geography

Durham University

[email protected]