Wet and Rather Cold
Temperatures
The average maximum temperature during December 2020 in Shoreham was 8.4 Celsius (47F), and that was about 1 Celsius (1.8F) below normal for the time of year. The average minimum temperature was 4.8 Celsius (41F), and that was around 0.5 Celsius (<1F) below the December normal.
The highest temperature recorded during the month was 12.4 Celsius (54F), on the 23rd, but there were 2 other days with highs above 12 Celsius (54F); both the 14th and 21st had maxima of 12.2 Celsius (54F). There were a further 8 days with maxima between 11 and 12 Celsius (52-54F) and another 2 days with highs above 10 Celsius (50F). All of these milder days occurred between the 11th and 26th. December had several cold days, and maximum temperatures were below 5 Celsius (41F) on 6 occasions. The 7th and 8th had highs of 4.2 Celsius (40F) and 3.5 Celsius (38F) respectively, but the other 4 cold days all occurred during the last week of December. On 2 of these cold days the high was below 4 Celsius (39F). The 29th had a high of 3.7 Celsius (39F), but the last day of the month was the coldest with a maximum temperature of 1.1 Celsius (34F). It was also the coldest day of the year.
A few mild nights occurred during December, and on 4 occasions the minimum temperature was above 10 Celsius (50F). The mildest night was the 22nd with a low of 11.3 Celsius (52F), but the preceding night was only a little less mild with a minimum of 11.1 Celsius (52F). All of the milder nights occurred between the 18th and 22nd. The coldest nights were generally at either end of the month. On 12 nights the minimum temperature was below 3 Celsius (37F), with 5 of these cold nights occurring between the 2nd and 9th, and another 6 nights between the 25th and the end of the month. Although lows of 0.1 Celsius (32F) and 0.5 Celsius (33F) occurred on the 7th and 10th respectively, the lowest values were in the last week of the month. On the 30th, a minimum temperature of minus 1.2 Celsius (30F) was recorded.
The sea temperature was around 11 or 12 Celsius (52-54F) at the beginning of December but fell to 9 or 10 Celsius (48-50F) by the end of the first week, and to 8 or 9 Celsius (46-48F) during the last week of December.
Frost
Air frost occurred on 3 nights during December, and that is average for the time of year. All frosts were slight, with minima of minus 0.2 Celsius (32F), minus 1.2 Celsius (30F) and minus 0.9 Celsius (30F) occurring on the 26th, 30th and 31st respectively. There were 12 grass frosts in December, and that’s 1 above average. With the exception of both the 9th and 14th, when grass minima of minus 2.5 Celsius (27F) and minus 2.8 Celsius (27F) occurred, the grass frosts occurred in the first and last weeks of the month. On both the 26th and 28th the grass minimum temperature was minus 3.9 Celsius (25F), but on the 30th the temperature dipped to minus 5 Celsius (23F).
Rain
Rainfall in December amounted to 174.6 millimetres (6.9 ins.). This was almost 90% above the monthly average, and appears to be one of the wettest Decembers in the area for nearly 90 years. Rain fell on 23 days, which is 3 days above average, and wet days (when 1 millimetre (0.04 ins.) or more of rain falls) numbered 20 days, and that was 5 days above average. The first day of the month was dry, but on the 2nd, rain in the afternoon and overnight amounted to 6 millimetres (0.25 ins.) and on the 3rd the total was 25.4 millimetres (1 inch). On the 5th another 5.2 millimetres (0.2 ins.) were added to the total, with 12 millimetres (0.5 ins.) falling on the 9th. Daily totals over 5 millimetres (0.2 ins.) occurred on the 11th, 13th, 18th and 19th, with 11 millimetres (0.4 ins.) measured on the 20th, nearly 10 millimetres (0.4 ins.) on the 21st, and 10.2 millimetres (0.4 ins.) on the 22nd. Less rain fell on the 23rd, a mere 8 millimetres (0.3 ins.) Between the 2nd and 23rd there were only 2 completely dry days, the 9th and 15th. The 24th and 25th were both dry, but 25.4 millimetres (1 inch) of rain fell on the 26th, with 20.6 millimetres (0.8 ins.) falling on the 28th. The last 3 days of the month were dry.
Hail
Soft hail fell during an early afternoon shower on the 5th, and small hail was observed for a couple of minutes during the evening of the 19th.
Thunder
No thunder was heard in this part of Shoreham.
Snow
No sleet or snow was observed in this part of Shoreham.
Wind
December was mostly a cyclonic month with mean sea level pressure some 9 millibars below average. The main areas of low pressure were generally over, or to the north of, Britain with winds blowing from a westerly point on 22 days, these equally divided between northwest and southwest. It was frequently windy, especially towards the end of the month. At Shoreham Airport, southwesterly gusts reached 37 knots (42 mph) on the afternoon of the 3rd, and 30 knots (34 mph) on the afternoon of the 13th, in the early hours of the 14th, and once again early during the evening on the 16th. Winds were quite squally on the 19th, and an isolated gust in the afternoon reached 35 knots (40 mph), with a gust of 33 knots (38 mph) occurring early on the 20th. The evening of the 26th became very windy, with the strong winds lasting until around dawn on the 27th. Southwesterly gusts reached 47 knots (54 mph) at midnight, and 54 knots (62 mph) just before dawn. These were the last significant gusts of the month.
Fog
There was fog on the evening of the 6th, this lasting until after mid morning on the 7th. Further patchy fog occurred through much of the morning on the 8th.
Statistics for December 2020
| Reporting Station | Highest Temp | Lowest Temp | Rain Total (mm) | Wettest | Rain days |
| Shoreham A/P | 13.3 | -2.2 | 123 | 20 | 23 |
| Thorney Island | 12.5 | -2.5 | 129 | 23 | 25 |
| Gatwick A/P | 13.0 | -2.8 | 125 | 24 | 23 |
| Herstmonceux | 13.5 | -2.0 | 176 | 36 | 24 |
| Bournemouth (Hurn) | 13.6 | -3.7 | 157 | 34 | 23 |
| Middle Wallop | 13.4 | -3.7 | 113 | 17 | 22 |
| Dieppe | 14.8 | -1.6 | 67 | 12 | 22 |