April is the middle month of meteorological spring, so as well as the traditional showers we might expect a steady increase in temperatures as the sun rises higher and the days grow longer. This year we got the showers, but temperatures actually fell as the month progressed and the last week of April was 1.4C cooler than the first. The average temperature for the month was 8.6C which is only a degree or so below normal, but a cold, dry polar airstream towards the end of the month made it feel colder than it was. We had colder Aprils in 2008, 2012 and 2013, but in those years April did at least finish up warmer than it started.
The rainfall total was 42.8mm which is right on the average – although it is often showery, April isn’t usually a particularly wet month. Despite occasional heavy showers there were no exceptional rainfall totals, and the wettest day was the 11th with 10.2mm.
Up to the 16th low pressure was in charge, with rain most days and a blustery spell around the 8th and a thunderstorm on the 14th. On the 16th a calm day with clear skies brought the highest temperature of the month at 17.9C, but even that was enough to spark off a heavy convective shower late in the afternoon.
Pressure began to build on the 16th, and from the 18th to the 21st whole the UK was under a large high pressure system. Although it was dry, there was high-level cloud which kept a lid on daytime temperatures but just allowed an air frost (-0.3C) early on the 17th.
The high moved away on the 21st, and for the next week we found ourselves between high pressure to our west and lows to our east. The result was a stream of cold, dry air fresh from the arctic keeping temperatures down and adding a noticeable chill factor. As this cold air met warm, moist air on its journey south, it generated some lively but very localised convective showers – April certianly lived up to its reputation in that respect – and on the 26th we were were treated to sleet in the morning (there was snow on the Brecon Beacons and Dartmoor) and a thunderstorm over the Bristol Channel during the afternoon. On the 28th it was cold enough for another overnight air frost.
Below-average temperatures in March and April mean that this spring is off to a cool start after our remarkably mild winter. Let’s hope May can put that right.