May did bring us some very welcome rainfall, the maximum on the 7th of 22.3mm relieved the parched ground. During the month there were several days with minimal rainfall, these, combined with 6.6mm on the 30th when there were almost eight hours of continous light rain, gave a total of 45.5mm which is 79% of the long-term average. It was a predominantly warm month with no extremes, the highest being 22.6°C on the 6th with the mean 0.8°C above the long-term average.
Looking at the figures for the Spring of 2011, I find that it was the warmest I have recorded and 1.6°C above the long-term average. The change in mean temperatures since I started recording in 1984 is quite remarkeable. It is no surprise to find that the total precipitation for Spring 2011 was very low and in fact a record for my station. With a total of only 64.6mm, which is just 36% of the long-term average, it beat the previous low of 66mm in 1990.
Another month with two distinct halves, the first being unseasonably cold and the latter produced both maxima and minima above the average for May. There were three nights with air frost, which burnt the early tender foliage of both vegetables and flowers, with a minimum of -1.4°C on the 12th. These were the latest spring air frosts since 2003. Fortunately, from the 17th as the pressure rose, so did the temperatures resulting in many warm days in the third week with a maximum of 27.8°C on the 24th, the warmest May day I have recorded. Overall the mean temperature was the lowest for May since 1996 at 0.45°C below the long-term average. The rainfall, totaling 32.7mm, was just 55% of the long-term average, the bulk of which fell on the 1st (15.1mm).
It was the coldest spring since 2001 being 0.1°C below the long-term average. The total rainfall for spring 2010 was also low, with a total of 130mm it was only 72% of the long-term average.
The month was noticeable for the relatively high average air pressure with the minimum not falling below 1000.0 Mb. This resulted in 17 totally dry days and when rain fell the daily totals were not large – 8.0mm on the 14th being the wettest day. With the rainfall for the month totalling just 31.7mm, being 52% of the long-term average, it was the driest May since 1998. Most of the shower activity centered around the 14th – 19th due to low pressure to the west of the country. As pressure rose again from an Azores high, temperatures picked up and brought glorious hot, sunny weather to conclude the month although maxima were trimmed due to brisk easterly winds. There were two nights with minimal air frosts on the 4th and 10th. May 2009 produced the 14th consecutive month with above average temperatures (+0.7°C) with the hottest day being the 29th when the thermometer peaked at 24.6°C.