Cold and Very Wet
Temperatures
The average maximum temperature during January 2021 in Shoreham was 6.8 Celsius (44F), and that was almost 2 Celsius (>3F) below normal for the time of year. The average minimum temperature was 2.4 Celsius (36F), and that was also nearly 2 Celsius (>3F) below the January normal.
The highest temperature recorded during the month was 11.8 Celsius (53F), on the 29th, but the previous day had a high of 11.3 Celsius (52F). On 2 other days, the 13th and 14th, temperatures rose above 10 Celsius (50F). On most days (19) the temperature rose to between 5 and 10 Celsius (41-50F), although 7 of these days had highs between 5 and 6 Celsius (41-43F). On 5 occasions the temperature failed to rise above 3 Celsius (37F), with all of these lower values occurring within the first 10 days of the month. There were 4 consecutive cold days beginning on the 7th, but the only day with a temperature below 2 Celsius (36F) was the 10th, when a high of 0.9 Celsius (34F) was recorded.
No especially mild nights occurred during January. In fact, only 9 nights had minimum temperatures above 5 Celsius (41F). The mildest night was the 20th, with a low of 9.2 Celsius (49F), but a further 4 nights had minima above 8 Celsius (46F). The coldest nights were early in the month and during the fourth week. On each of the first 11 nights of January the temperature fell below 3 Celsius (37F) and 5 consecutive nights, beginning on the 22nd, had minima below 0 Celsius (32F). The lowest temperature was minus 3.4 Celsius (26F) on the 8th, but minus 2.9 Celsius (27F) was recorded on the 10th, and minus 2.7 Celsius (27F) occurred on the 24th.
The sea temperature was around 8 or 9 Celsius (46-48F) at the beginning of January, but for much of the month it was nearer to 7 or 8 Celsius (45-46F).
Frost
Air frost occurred on 11 nights during January, and that was 8 days above average for the time of year. Most of the frosts were slight and occurred in 2 spells. The 7th to the 10th, and the 22nd to the 26th inclusive. The exceptions were on the 1st and 18th, when slight frosts gave minimum temperatures of minus 0.1 Celsius (32F) and minus 0.8 Celsius (31F) respectively. There were 13 nights with grass frosts, which is 1 above the average. The lowest grass minimum temperature was minus 7.8 Celsius (18F) on the 24th, but minus 7.2 Celsius (19F) occurred on the 26th, and on a further 3 nights the grass temperature fell to minus 5 Celsius (23F) or lower.
Rain
Rainfall in January amounted to 102.4 millimetres (4 ins.). This was more than double the monthly average. Rain fell on 24 days, which is 6 days above average, and wet days (when 1 millimetre (0.04 ins.) or more of rain falls) numbered 19 days, and that was 7 days above average. Precipitation was measured on the first 7 days of the month, but most of it was light, with the highest daily total only 3.2 millimetres (0.1 ins), this occurring on the 5th. In fact, the reading of 0.4 millimetres (0.02 ins.) on the 7th was entirely made up of melted frost and dew. The 8th, 9th and 10th were all completely dry days, with only 2 other completely dry days observed during the rest of January. Daily totals of 5 millimetres (0.2 ins) or more were measured on the 14th, 15th and 16th, and after a dry day on the 17th, a further 2 consecutive days received more than 5 millimetres (0.2 ins.) of rain. The last completely dry day occurred on the 25th, and this was followed by some of the heaviest rain of the month. The last 6 days of January had over 43 millimetres (1.7 ins.) of rain, including daily totals of 14.8 millimetres (0.6 ins.) on the 27th and 11.6 millimetres (0.45 ins.) on the 28th.
Hail
No hail was observed in this part of Shoreham.
Thunder
No thunder was heard in this part of Shoreham.
Snow
A little sleet fell in a shower around dawn on the 6th. Sleet was observed briefly late morning on the 24th and light snow fell late evening on the same day, although it failed to settle.
Wind
Winds were predominantly from the north or northwest during January, accounting for just over half the monthly total. The remaining days were fairly evenly divided between northeast and southwest winds. During the first half of the month, gentle or moderate breezes blew, but in the second half of January, the wind was often fresh or strong. At Shoreham Airport, a southerly gust of 30 knots (34 mph) occurred on the morning of the 16th, the first significant gust of the month. The 19th, 20th and early part of the 21st were windy, with southwesterly gusts of 35 knots (40 mph) in the early hours of the 19th, a gust of 38 knots (43 mph) on the evening of the 20th, and 46 knots (53 mph) around midnight on the 21st. Southwesterly winds again on the 29th gusted to 37 knots (42 mph) in the late morning, but on the 30th winds became northeasterly and a gust of 31 knots (35 mph) was measured in the late morning.
Fog
There were 4 days when fog was observed at the mid morning observation. On the 9th there was mist, fog and low cloud in the morning, with fog returning in the evening. Dense freezing fog occurred on the morning of the 10th, and fog formed for a while after overnight rain on the 13th. Lastly, sea fog formed between rain bands on the morning of the 28th.
Statistics for January 2021
| Reporting Station | Highest Temp | Lowest Temp | Rain Total (mm) | Wettest | Rain days |
| Shoreham A/P | 12.0 | -5.2 | 78 | 14 | 23 |
| Thorney Island | 12.2 | -4.1 | 70 | 12 | 20 |
| Gatwick A/P | 13.4 | -4.8 | 106 | 17 | 22 |
| Herstmonceux | 12.4 | -4.7 | 99 | 17 | 22 |
| Bournemouth (Hurn) | 13.3 | -5.2 | 98 | 19 | 20 |
| Middle Wallop | 13.3 | -2.9 | 90 | 19 | 20 |
| Dieppe | 13.2 | -3.4 | 101 | 13 | 23 |