Marlborough's weather: May was cool, but together the three months of Spring were warmer than average

Written by Eric Gilbert on .

A May peacock (Photo: Eric Gilbert)A May peacock (Photo: Eric Gilbert)It was a cool May with the mean temperature just below average. The statistics show that although the daytime temperatures were in fact above average they were offset by the many cold nights that meant the mean minimum was 1.1C below average.  

There was only one air frost - with -1.2C recorded on May 5 - but several nights gave a ground frost with no evidence above ground - especially during the early days of May.

Warm air brought to us on a south-westerly air flow from Iberia, meant a warmer end to the month with the warmest night on May 31 with a minimum of 13.9C, which was 6.8C above the 35-year average.

Although the mean temperature for last month of Spring was below average, the season was warmer than normal (+0.8C) with a mean of 9.71C. 

It is interesting to analyse the data since my station began recording in 1984 and find that Spring of that year was exceptionally cold with a mean of 6.83C.  Investigating the statistics for that year I found that March was 2.1C below average, April 1.1C lower than average and May a significant 2.2C below the current average. By contrast, the Spring of 2011 produced a mean of 10.51C, the warmest from my records.

During that particularly cold Spring of 1984, hard frosts occurred on April 2 and 4 with the thermometer falling to -6.0 and -5.0C. This followed a cold March that produced 11 air frosts, the coldest of which was -3.5C on March 29.

Contrasting 1984 with the warmest Spring in 2011, although a hard air frost measuring -6.3C was recorded on 8 March 2011, no air frost occurred after March 26 or for the whole of April and May. 

Although the examples above cover the past 35 years, the graph for this period shows an almost continuous rise in the mean temperature with the exception of the cold Springs in 1996 and 2013.

Rainfall in May 2018 was concentrated on three days, May 7 - 9, when over half the month’s precipitation fell - and 6.2mm, 14.4mm and 14.0mm respectively was recorded. The total rainfall for the month almost equalled the average with 59.5mm against the average of 61.0mm. 

There were only six days classified as wet days when the precipitation was equal to or greater than 1mm and 21 dry days in May.

The trend of drier than average rainfall continues into 2019. The rainfall for 2018 was 62mm below the 35-year average at 783mm. 

The first five months of 2019 have produced a total of 301mm a deficit of 55mm compared to the 35-year average. However, set against that figure must be the loss through evaporation from ground sources and plant life, the equivalent of 237mm rainfall. 

The year of 2018 was not the driest I have recorded, as that occurred in 1996 with 594mm of precipitation whereas six years later, in the very wet year of 2002, 1,146mm was recorded. 

It may or may not be a taste of days to come, but June 1 was the hottest day in Marlborough since 7 August 2018.

There is more information - with daily statistics - on Eric Gilbert's Windrush Weather website.