A very dry April in Scotland

The second month of the Spring is going to end soon but will be certainly remembered as one of the driest and mildest in many areas of the UK. Focusing on Scotland, the eastern side has seen very dry conditions for several weeks, with numerous sunny and mild days.

Indeed, if we consider the maximum and minimum temperatures observed in Edinburgh (Figure 1), many days have experienced mild conditions (Max temp>15°C) instead only two days have seen frost (14th, 19th, whilst the long term average sees 4days). The average temperature up to April 26th is 8.97°C (+1.1°C above the 1981-2010 average of 7.8°C).

Figure 1. Max and min temperatures observed in April 2020. Note last day is 26th. (Data source: Meteociel).

But the most significant aspect of the last few weeks has been the lack of rainfall in many areas, with several days of sunshine. Figure 2 shows the daily hours of sunshine and the daily rainfall amount observed in Edinburgh during the last month.

Figure 1. Daily rainfall (blue) and hours of sunshine (yellow) observed in April 2020. Note last day is 26th. (Data source: Meteociel).

We can see that no significant rainfall has been oberved, with less that 1mm of cumulative rain up to April 26th. And if we consider the World Meteorological Organisation (WMO) definition of rain day (i.e. cumulative daily rainfall must be >=1.0mm), then no rain day has occurred yet. On the other hand, long sunny days have been observed, with a total of 176h of sunshine in 4 weeks. The climatology sees 136h, thus it is clear that this has been a very unusual April.

These dry conditions have been caused by an almost stationary high pressure close to the UK which has caused a NE drifts of most lows and troughs towards Iceland and Scandinavia (causing very dry conditions also across central Europe and the Mediterranean).

The next few days will see a cooler trend, with temperatures close or slightly below the average, but still in a mostly dry condition with only few showers at times. Thus, it is likely this April will be one of the driest ever recorded in the area!