It is said that a British summer is three nice days then a thunderstorm - and that's exactly what happened in late April 2018.
By Ian Mills (Ian Mills Consulting)
In late April a large omega block developed with the anticyclone over Europe. This led to a warm southerly airstream affecting the UK.
Under the influence of this air stream on 18 and 19 April much of Europe experienced clear skies and hot temperatures, for example reaching 29 °C in the south of England.
In the Meteosat-11 Airmass RGB, 19 April 12:00 UTC (Figure 1, top right, click to expand) the lows on the left and right flank the large anticyclone over Europe. The white cloud stretching from the west of Portugal north across Ireland and Scotland shows the position of a weak cold front and the associated jet stream flowing north.
Figure 2: Meteosat-11 Airmass RGB animation, 21 April 13:00–21:00 UTC
The southwest of England also experienced pleasant sunny warm weather, but it all came to an end on 21 April. The animation of the Airmass RGB, 21 April 13:00 to 21:00 UTC (Figure 2) shows a storm first developing over the Brest Peninsula in France. It moved north and developed and arrived on the Devon coast around 16:30 UTC.
More storms can be seen travelling north from France to hit southern England around the same time.
So the summery conditions came to an end and the subsequent weather was cool, windy and cloudy.
The UK wasn't alone in experiencing the cloud-free conditions with high temperatures during that period, as can be seen on the Meteosat-11 Natural Colour RGB with surface observations overlaid, 19 April 06:00 UTC (Figure 3).
According to preliminary temperature anomaly analysis from the NOAA Climate Prediction Center central Europe was 7–9 –C, and parts of Germany were over 9 °C warmer than average (Source: @severeweatherEU/NOAA).