Weather in South London during December 2009
Cold and rather wet. The coldest December since 2001 and the wettest since 2002.
Temperatures
The average maximum temperature during December 2009 was 6.6 Celsius (44F), and that was 1.5 Celsius (3F) below the 20-year normal, and 1.4 degrees Celsius (2.5F) below the 100-year normal. The average minimum temperature was 2.0 Celsius (36F), and that was 1.6 Celsius (3F) below the 20-year average, and 0.3 Celsius (<1F) below the 100-year normal.
The highest temperature recorded during December was 12.5 Celsius (55F) on the 9th, but although the temperature rose above 10 Celsius (50F) on 5 other occasions, all of these mild days occurred within the first 10 days of the month. After the 13th, there were only 2 days when maxima exceeded 6 Celsius (43F), namely the 26th and 27th. The coldest weather of the month was in the third week. The 16th was the coldest day with a maximum of 1.7 Celsius (35F), but the 19th was only 0.2 Celsius less cold.
There was just 1 very mild night during December. On the night of the 5th/6th the temperature only fell to 11.2 Celsius (52F). On the following night the temperature fell to 7.5 Celsius (45F), the second mildest night of the month, and there were only 5 other nights when the temperature stayed above 6 Celsius (43F) with all of these milder nights occurring before the 11th. The temperature fell below 0 Celsius (32F) on the first night of December, and again on the night of the 27th/28th. Otherwise, all the cold nights occurred between the 11th and 23rd. On the night of the 15th/16th a minimum of minus 5.4 Celsius (22F) was recorded, with minus 5.1 Celsius the overnight reading on the 22nd/23rd.
Frost
There were 10 air frosts during December, and that was 3 more than normal. A total of 15 grass frosts were recorded, and that was 2 more than normal. All bar 4 of the grass frosts occurred between the 11th and 23rd. On 6 nights, the grass temperature fell below minus 5 Celsius (23F) and this included 3 nights, the 15th/16th, 20th/21st and 22nd/23rd when minus 8 Celsiu (18F), or lower, was recorded. The coldest night on the grass was the 15th/16th with minus 8.7 Celsius (17F).
Rain
A total of 79.3 millimetres (3.1ins) of rain fell during December and this was over 30% above the 20-year average. There were only 4 completely dry days, although there were 6 other days with negligible rainfall. Wet days (1.0mm/0.04 ins, or more) numbered 15, and that was 6 days above average. The second week had mostly light rain, otherwise precipitation during the month was fairly evenly distributed. There were only 5 days when the total exceeded 5 millimetres (0.2ins) including 2 days when 10 millimetres (0.4ins) fell. The wettest day of the month was the 29th with 12.7 millimetres (0.5ins).
Thunderstorms
There was a thunderstorm consisting of lightning and 3 nearby claps of thunder from 2038 to 2131 on the 23rd..
Hail
A soft hail (snow pellets) shower fell around mid morning on the 17th, and small 'ordinary' hail was observed at 2020 on the 23rd.
Snow
Sleet or snow was observed on 7 days during December, 5 days above average. More than half cover of snow was reported on 3 mornings, and that was 2 above the December average. The first snow fell from late mornng until mid afternoon on the 16th. It was moderate at times and settled to 1-2cm but, following rain, it had mostly thawed by the following morning. Light snow showers on the afternoon of the 17th merged into longer spells of mostly light snow during the evening. Further light snow showers fell overnight with 1cm measured on the morning of the 18th. Snow partially thawed but less than half cover persisted for the following 3 days. Sleet fell in the early hours of the 20th and sleet also fell for much of the 21st. Moderate snow fell late afternoon and early evening, this settling, with 1cm still covering the ground on the following morning despite some overnight rain and sleet. The snow cover was still present on the morning of the 23rd. Sleet briefly fell on the evening of the 23rd, but lying snow continued to tha and disappeared completely during the 24th.
Wind
Gentle or moderate southwest winds were dominant in the mild early part of the month, but on the 6th a fresh southwest wind produced a gust of 33 kn (38 mph). An anticyclone was responsible for some light and variable winds during the second week, but through the remainder of the month the direction varied between northeast and southwest. However, in the last 4 days of the month moderate northeast winds prevailed.
Fog
Wet fog occurred early on the 11th, this lasting until after mid morning.
Monthly figures for December in, and around, London
The average maximum temperature during December 2009 was 6.6 Celsius (44F), and that was 1.5 Celsius (3F) below the 20-year normal, and 1.4 degrees Celsius (2.5F) below the 100-year normal. The average minimum temperature was 2.0 Celsius (36F), and that was 1.6 Celsius (3F) below the 20-year average, and 0.3 Celsius (<1F) below the 100-year normal.
The highest temperature recorded during December was 12.5 Celsius (55F) on the 9th, but although the temperature rose above 10 Celsius (50F) on 5 other occasions, all of these mild days occurred within the first 10 days of the month. After the 13th, there were only 2 days when maxima exceeded 6 Celsius (43F), namely the 26th and 27th. The coldest weather of the month was in the third week. The 16th was the coldest day with a maximum of 1.7 Celsius (35F), but the 19th was only 0.2 Celsius less cold.
There was just 1 very mild night during December. On the night of the 5th/6th the temperature only fell to 11.2 Celsius (52F). On the following night the temperature fell to 7.5 Celsius (45F), the second mildest night of the month, and there were only 5 other nights when the temperature stayed above 6 Celsius (43F) with all of these milder nights occurring before the 11th. The temperature fell below 0 Celsius (32F) on the first night of December, and again on the night of the 27th/28th. Otherwise, all the cold nights occurred between the 11th and 23rd. On the night of the 15th/16th a minimum of minus 5.4 Celsius (22F) was recorded, with minus 5.1 Celsius the overnight reading on the 22nd/23rd.
Frost
There were 10 air frosts during December, and that was 3 more than normal. A total of 15 grass frosts were recorded, and that was 2 more than normal. All bar 4 of the grass frosts occurred between the 11th and 23rd. On 6 nights, the grass temperature fell below minus 5 Celsius (23F) and this included 3 nights, the 15th/16th, 20th/21st and 22nd/23rd when minus 8 Celsiu (18F), or lower, was recorded. The coldest night on the grass was the 15th/16th with minus 8.7 Celsius (17F).
Rain
A total of 79.3 millimetres (3.1ins) of rain fell during December and this was over 30% above the 20-year average. There were only 4 completely dry days, although there were 6 other days with negligible rainfall. Wet days (1.0mm/0.04 ins, or more) numbered 15, and that was 6 days above average. The second week had mostly light rain, otherwise precipitation during the month was fairly evenly distributed. There were only 5 days when the total exceeded 5 millimetres (0.2ins) including 2 days when 10 millimetres (0.4ins) fell. The wettest day of the month was the 29th with 12.7 millimetres (0.5ins).
Thunderstorms
There was a thunderstorm consisting of lightning and 3 nearby claps of thunder from 2038 to 2131 on the 23rd..
Hail
A soft hail (snow pellets) shower fell around mid morning on the 17th, and small 'ordinary' hail was observed at 2020 on the 23rd.
Snow
Sleet or snow was observed on 7 days during December, 5 days above average. More than half cover of snow was reported on 3 mornings, and that was 2 above the December average. The first snow fell from late mornng until mid afternoon on the 16th. It was moderate at times and settled to 1-2cm but, following rain, it had mostly thawed by the following morning. Light snow showers on the afternoon of the 17th merged into longer spells of mostly light snow during the evening. Further light snow showers fell overnight with 1cm measured on the morning of the 18th. Snow partially thawed but less than half cover persisted for the following 3 days. Sleet fell in the early hours of the 20th and sleet also fell for much of the 21st. Moderate snow fell late afternoon and early evening, this settling, with 1cm still covering the ground on the following morning despite some overnight rain and sleet. The snow cover was still present on the morning of the 23rd. Sleet briefly fell on the evening of the 23rd, but lying snow continued to tha and disappeared completely during the 24th.
Wind
Gentle or moderate southwest winds were dominant in the mild early part of the month, but on the 6th a fresh southwest wind produced a gust of 33 kn (38 mph). An anticyclone was responsible for some light and variable winds during the second week, but through the remainder of the month the direction varied between northeast and southwest. However, in the last 4 days of the month moderate northeast winds prevailed.
Fog
Wet fog occurred early on the 11th, this lasting until after mid morning.
Monthly figures for December in, and around, London
| Place | Maximum | Minimum | Rainfall (mm) |
| C. London | 13.8 | -2.0 | 88 |
| Heathrow A/P | 12.8 | -4.6 | 83 |
| Gatwick A/P | 12.5 | -7.8 | 123 |
| Croydon | 11.5 | -5.6 | 98 |
| Northolt | 12.6 | -5.2 | 82 |
| Farnborough | 12.5 | -7.2 | 106 |
| Stansted A/P | 12.2 | -5.4 | 70 |