Marlborough's July weather: in case you've forgotten - the figures confirm those interrupted picnics & an interrupted grain harvest

Written by Eric Gilbert on .


July 2017 was not a month to remember as a good summer month - it did not produce much glorious sunshine with recurring high temperatures and as they raced to make the most of the dry days, farmers will remember the month for a continually interrupted grain harvest.

The very changeable month, after the first week, was due to a succession of depressions passing over or near the UK. The barometric pressure in Marlborough was 2mb below the long-term average.

Although the mean temperature was just above the 33-year average (+0.27C), this figure masks the fact that the average daytime temperature was 0.2C below the long-term average. The many cloudy nights gave a contrasting picture as the average minimum was above the long-term average (+0.6C). During such nights the cloud acts as a blanket to stop heat radiating back into the atmosphere.

The month started with several very warm days, the peak being reached on July 6 with a maximum of 29.9C, but from July 11 onwards the temperatures fell away during the daytime. There were two days when the thermometer only reached 17.3C (July 22 and 23) - that was a significant 5C below the 33-year average.

Low-pressure systems bring cloud that mask the sun and bring precipitation. There were many days when bands of showers, some heavy, transited the Marlborough area. There were nine dry days before July 11, but only six after that date.

The wettest day occurred on July 11 when a considerable rainfall total was recorded of 26.2mm. There were two additional days, July 21 and 29, when rainfall totals were in double figures - 23.5mm and 14.8mm respectively.

The rainfall total for all of July came to 97.4mm, making it the wettest July since 2009. This total was 163% of the 33-year average or plus 37.6mm.

It is interesting to note that the five wettest July months have occurred since 2002 (my records go back to 1984). In July 2007 I recorded a total of 127.2mm and 2009 amounted to 113.0mm.

I recorded 117 hours of strong sunshine, slightly better than the past two years since this instrument was installed. However, global sunshine, which includes reflected strong light, was 11 hours down on the average for the past 11 years.

During the periods of strong sunshine - including latter July days when there were only brief bursts - the UV levels rose into the ‘Very High’ category on 19 days. The peak reading registered was on July 16 and that was almost into the ‘Extreme’ category.

Meteorologists keep diurnal temperature records - noting the daily range of temperature from the maximum to the minimum. As humans we have to adapt to these ever-changing conditions. A good example occurred this month. On July 2, the diurnal temperature range was 23.4C (24.2C to 1.0C) and in contrast July 19 had a range of just 3.0C (19.4C to 16.4C).

Apart from holding back the local grain harvest, elsewhere July's inclement weather was not kind to the wild sea birds such as puffins that visit Britain's shores to breed.  They too need good and calm weather to collect food to feed up their young before the colonies leave again for a winter at sea.

Puffin on Skomer (Photo: Eric Gilbert) Puffin on Skomer (Photo: Eric Gilbert)