Voice

of the Villages

Weather watch

February 2024

An analysis of trends in local weather over the month of February. There is also a discussion of the time between heavy rainfall and flooding. This page is contributed by Richard Seaton of Offchurch.

‘February fill-dyke’ certainly lived up to its name this year. And not only dykes were filled but also water butts, underground aquifers and reservoirs. However, the rains caused major problems to farmers, homeowners and drivers as the ground became saturated and rivers overflowed. Fields and roads were flooded. The bridge at Offchurch was closed on at least three occasions.

Across the UK record rainfall totals were logged. In Offchurch 142.4 mm of rain fell, over three times the average of 42.2 mm, making this the wettest February in the village since records began 26 years ago. The good news is that the ground is now irrigated to a considerable depth, which should ensure good tree growth and possibly no ‘hosepipe bans’ this year. However, despite all the rain there were 8 dry days this month.

It was a very mild month; the average temperature was 8.1°C, which is 3.2°C above the average for the area and has set a record for the warmest February since records began. The highest daytime temperature was 16.7°C on the 15th. Most nights were also mild with just two air frosts and 11 grass frosts. The coldest night was the 25th when the temperature fell to just -2.3°C.

Surprisingly, despite all the rain we had no named storms! The sea-level atmospheric pressure rose to 1034 hPa on the 1st but fell to 976 hPa by the 9th. The average pressure was 1010 hPa. Winds were mainly from the southwest with a maximum gust of 27 mph on the 26th.

There were seven days with no sunshine at all, with a total for the month of 53 hours, which is seven percent below the February average. Note how the UV Index readings (in red on the chart) are rising as the month progresses. This is due to the sun gradually rising higher in the sky.

Why doesn’t the bridge at Offchurch and other places flood while it’s raining?

“It poured with rain all day and yet the bridge was clear of water in the evening. It was dry overnight and yet the next morning the bridge was flooded and remained so most of the day even though there was no more rain.” This delay experienced in Offchurch and other places where roads are prone to flooding after prolonged heavy rain is due to the time taken for the excess water to drain into the rivers. Whilst the immediate rainfall into the river has some effect on the water level, it’s the rainfall over the countryside, which drains into gullies, brooks and streams, and eventually into the rivers that causes the rivers to flood. After all, the surface area of the river is small compared to that of the surrounding countryside. Of course, the actual amount of water eventually reaching rivers is dependent on the saturation level of the ground. Given that last autumn and this winter were so wet, it is likely the ground was already saturated before the start of February.

The chart shows the change in river level during a spell of heavy rain (30 mm) over a period of five days from 18:00 hours on 15 February to 18:00 on the 20th. I have used millimeters for rainfall and centimeters for the change in the level of the river so that an easy comparison between the two readings can be made. It may be seen that after the rain stops it takes around 18 hours for the river level to rise to a peak and a similar time for it to fall back, if the weather remains dry. From the chart it appears that about 10 mm of rainfall causes a rise in river level of some 50 mm (5 cm).

The photo shows the state of the bridge at Offchurch on 19 February at 9.00 am – incidentally it looks as though the vehicle is about to lose its number plate! It could have been a lot worse, some vehicles started to float as they tried to pass through the water and others broke down. Actually, several number-plates were recovered when the floods subsided.

Details regarding the state of local rivers may be found by entering your postcode on the ‘check for flooding’ government website, which is where I downloaded the data for the chart [2].

[1] Thanks to Clare Philpot of Offchurch for permission to use her photograph.
[2] https://check-for-flooding.service.gov.uk/find-location

For local weather details and forecasts go to: https://offweather.hopto.org

Richard Seaton

rkseaton@outlook.com