Very Dry and Cold
Temperatures
The average maximum temperature during April 2021 in Shoreham was 12.8 Celsius (55F), and that was about 2.5 Celsius (4.5F) below normal for the time of year. The average minimum temperature was 2.9 Celsius (37F), and that was around 4 Celsius (7F) below the April average. Overall, it was the coldest April in the area since 1986, or perhaps 1983. Average minimum temperatures have not been lower in the last 56 years.
The highest temperature recorded during the month was 17.6 Celsius (64F), on the 24th, although the 23rd was not far behind with 17.3 Celsius (63F). Only 3 other days had maxima above 15 Celsius (59F0, and the 1st, with a high of 15.7 Celsius (60F), was the only one of these milder days to occur before the 20th. On most days (18) maxima were between 10 and 14 Celsius (50-57F), but several cold days occurred during the early part of the month. On 4 days the temperature failed to reach 10 Celsius (50F), with all of these cold days falling between the 5th and 10th. On the 10th a high of 8.0 Celsius (46F) was recorded, but the coldest day was the 7th with a maximum temperature of just 7.5 Celsius (45F).
Anticyclonic weather, the mean sea level pressure was some 8 millibars above average, led to many calm and clear nights. As a result, there were very few mild nights. The first night of the month had a low of 10.3 Celsius (50F), but thereafter, the 24th, with a low of 7.2 Celsius (45F) was the only other night with a minimum above 6 Celsius (43F). A further 3 nights had lows between 5 and 6 Celsius (41-43F), but the majority of nights (21) recorded minima between 0 and 5 Celsius (32-41F). Colder nights did occur, and on both the 7th and 13th minimum temperatures of minus 1.8 Celsius (29F) were measured.
The sea temperature was around 9 Celsius (48F) during most of April, but struggled closer to 10 Celsius (50F) towards the end of the month.
Frost
Air frost occurred on 3 nights during April, and that was a couple of nights above average for the time of year. However, there were 19 grass frosts, and that was a remarkable 15 more than can be expected in a normal April. The 7th, 12th and 13th each had air frosts, but the air temperature fell to between 0 and 1 Celsius (32-34F) on 6 nights, and these nights had fairly low grass temperatures. Although no grass frosts occurred on the first 5 nights of April, only the 10th and 21st were completely frost-free between the 6th and 23rd. Grass frost was also observed on 3 out of the last 4 nights of the month. On many nights (10) the grass frost was slight with minimum readings between 0 and minus 2 Celsius (32-28F), but particularly early in the month, grass temperatures were much lower. On 3 nights, the 7th, 12th and 13th, grass minima were below minus 5 Celsius (23F), with the lowest value of minus 6.7 Celsius (20F) occurring on the 13th.
Rain
Rainfall in April amounted to just 2.3 millimetres (0.1 ins.). This was about 7% of the monthly average. Measurable rain fell on 3 days, which is 6 days below average, and wet days (when 1 millimetre (0.04 ins.) or more of rain falls) numbered 1 day, and that was 5 days below average. Although it was only the driest April in the area since 2007, it ranked in the top 5 dry Aprils in 140 years of local records. Almost uniquely, the first day of April was, like the first day of March, cloudless. A little precipitation occurred on 3 out of the first 9 days of the month, but not enough to dampen the ground. On the 10th the rain was just measurable (0.1 millimetres (less than 0.01 ins.) but only measurements of 0.2 millimetres (0.01 ins.) are considered to be significant. On the following day, the 11th, afternoon showers, followed by overnight precipitation gave 0.8 millimetres (0.03 ins.) with 0.2 millimetres (0.01 ins.) on the following day. No more measurable rain fell until the 28th, when light rain during the day produced 1.2 millimetres (0.05 ins.). Light showers occurred on the 30th, but failed to add anything to the monthly total.
Hail
No hail was observed in this part of Shoreham.
Thunder
No thunder was heard in this part of Shoreham.
Snow
Light sleet and snow showers occurred early and late in the afternoon on the 6th, and sleet, with a little wet snow, was observed on the morning of the 12th.
Wind
With high pressure dominating, winds were often light, especially at night, and directions were variable, although northeasterly breezes accounted for almost a third of the observed directions, and several mornings had northwesterly winds blowing down the Adur valley. At Shoreham Airport, the weather station was not operational between the 9th and 19th, but during the remainder of the month there were no gusts of 30 knots (34 mph) or more reported.
Fog
Patchy sea fog occurred for a while in the afternoon on the 20th,
Statistics for April 2021
| Reporting Site | Highest Temp | Lowest Temp | Rain Total (mm) | Wettest | Rain days |
| Shoreham A/P | 16.7 | -2.7 | * | * | * |
| Thorney Island | 16.1 | -3.0 | 1.4 | 0.6 | 3 |
| Gatwick A/P | 17.5 | -4.9 | 7 | 2 | 4 |
| Herstmonceux | 16.3 | -3.5 | 5 | 3 | 6 |
| Bournemouth (Hurn) | 17.3 | -5.2 | 9 | 4 | 5 |
| Middle Wallop | 17.8 | -2.6 | 19 | 13 | 4 |
| Dieppe | 17.8 | -2.2 | 19 | 15 | 5 |
* Data missing