A popular weather saying at this time of year is ‘April showers’, but where does this originate and what’s special about April?
The full proverb is “March winds and April showers bring forth May flowers”, dating back over 125 years.
This suggests that flowers grow and prosper thanks to all the rain that falls in April.
Yet, climatologically, April is one of the drier months.
For example, the Bucks average April rainfall is around 50mm, 25% less than in some of the autumn months.
There is no doubt, however, that as we move through spring, the strengthening sun warms up the ground much more than on a similarly clear day in say December.
This surface heating creates thermals (convection), pockets of warm air which ascend from near the ground due to their buoyancy.
As the air rises, it cools and can no longer hold all its moisture, the excess condensing out into water droplets, ie cloud – and then, if the buoyancy is sufficiently strong and so the cloud grows deep enough, showers develop.
Whilst April is one of the more favourable months for this to occur, it is just as likely at any time during spring or summer, and the term ‘June’ or ‘July showers’ would be equally apt – think how often we see rain shower interruptions at the Wimbledon tennis tournament for example.
Driven by convection, these showers usually die away quickly during the evening across inland areas. Any showers that remain tend to be concentrated near windward coasts, where the relatively high sea temperature compared to the land at night can allow convection to continue.
Across south-eastern Britain, much of our precipitation in spring and summer comes from these daytime showers, rather than the frontal activity that is the dominant contribution to rainfall totals during autumn and winter.
As for the forecast over the coming days, there’ll be plenty of ‘April showers’ around in the Aylesbury Vale area during the rest of the week, although some warm sunshine too. The showers could be heavy and thundery at times and may merge into longer spells of rain over the weekend.