22nd May 2018
Established 1872. Online since 1996.

Mild, wet, and just a little bit hot

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JULY was a mild, wet month with a few “hot” days.

The 1st to the 13th was rather unsettled and cyclonic. A depression moved north to the west of the UK during the first few days, with several lows then tracking east or north-east across the British Isles in quick succession.

From the 14th to the 23rd – with pressure high to the south of the UK – depressions tracked north-east between Scotland and Iceland, bringing an unsettled westerly airflow across northern Scotland.

Towards the end of this period, a low taking a more southerly track east across the Northern Isles brought a brief cooler north-westerly interlude.

From the 24th until the end of the month it was less unsettled. As an anticyclone developed over Scandinavia, while pressure remained low to the west of the British Isles, a warm and sometimes moist south-easterly airflow became established over Shetland, The month began with a depression to the west of the British Isles feeding moist south-easterly winds across Shetland, and a waving front moving erratically east against high pressure over Scandinavia. As a result, the 1st and 2nd were rather cloudy and misty days, with outbreaks of heavy rain and only a few brighter, drier spells.

The 3rd started mainly dry and bright but rain, mist and fog spread back from the east as the decaying front returned west across Shetland and winds eased light easterly. The rain – heavy for a time overnight – died out and the mist cleared during the morning of the 4th to leave a fine afternoon with light winds.

Mist and fog returned overnight, but soon cleared back to eastern coasts and headlands on the 5th, as a weak ridge built across Shetland giving most a fine, sunny day. A temperature of 18.9° Celsius was recorded at Lerwick, and 18.2° Celsius on Fair Isle –- the hottest day there since the 19.9° Celsius of July 2006. During the evening, as east to north-easterly winds freshened, the inevitable low cloud and fog spread in quickly from the east. However, this lifted into low cloud overnight as north-easterly winds freshened.

Unfortunately, the taste of summer was not to last. As an Atlantic depression tracked east across the British Isles to become slow-moving over the northern North Sea, unsettled, cloudy conditions with brisk cool north to north-easterly winds then became the order of the day for the next week across north-east Scotland. However, precipitation amounts were generally small at first.

Later on the 11th, misty conditions with hill fog spread in from the east. Heavy rain accompanied by strong northerly winds followed overnight as the low – deepening slightly as it tracked north towards southern Norway – pushed a front west across Shetland.

The fog and rain cleared early on the 12th, though the strong northerly wind eased only slowly during the day. As the persistent cloud-sheet began to show signs of breaking, one or two places were even lucky enough to see a glimpse of evening sunshine.

The 13th, though remaining disappointingly cloudy, was dry with light winds for the most part, as a ridge crossed the area from the west. With pressure low over Iceland, a moist south-west to westerly airflow brought generally cloudy conditions with outbreaks of rain and hill fog from early on the 14th. The fresh winds backed southerly later in the day, as a developing low ran quickly north-east towards north-west Scotland, bringing further rain, mist and fog by the evening.

As the low tracked quickly past Shetland, its cold front cleared east early on the 15th, leaving a bright and showery day with strong to gale-force westerly winds across the area.

Though rather cloudy with some patchy drizzle, winds eased during the 16th, as filling low pressure moved away into the Norwegian Sea. With pressure building weakly across the area, the 17th was a much brighter, mainly dry day with light winds.

The 18th soon clouded over, with heavy rain quickly spreading from the south-west as another low ran north-east towards Orkney. Early on the 19th, as the low continued past Shetland towards south-west Norway, mist and low cloud soon lifted and light cyclonic winds quickly increased strong north-westerly, bringing rather cloudy and cool conditions with patchy rain or showers.

The 20th and 21st – though still generally cloudy – became drier as north-westerly winds eased.

On the 22nd damp and cloudy weather spread from the south-west, as a depression – tracking east across Iceland – trailed fronts through the area in a mild south-westerly airflow. However, as an anticyclone developed over Scandinavia during the 23rd, this was replaced by dry, brighter conditions and winds became light south-east to easterly.

The anticyclone persisted over Scandinavia through to the end of the month, maintaining a mild south-east to easterly airflow over Shetland. This brought some warm, sunny conditions, with Lerwick reporting its warmest and sunniest day of the month on the 29th, with 20.8° Celsius and 12.9 hours sunshine.

Unfortunately, with low pressure to the west of the British Isles attempting to push fronts east against the high pressure, the added moisture brought days with low cloud, fog and the occasional outbreak of mainly light showery rain at times.

Lerwick’s hottest days have been 22° Celsius (72°F) on 8th July 1971, and 23.3° Celsius (74°F) on 4th and 5th August 1982.

The temperature reached 25.3° Celsius (77.5°F) at Baltasound on 2nd July 1958.

On 6th August 1910 27.8° Celsius (82°F) was reported by the keepers at Sumburgh Head Lighthouse. However, the exposure of the thermometer is unknown, so there are doubts about the accuracy of this reading.

Mean temperature – 14.0°C (1.4°C above average). Rainfall – 108.9 mm (114 per cent of average). Sunshine – 135.2 hours (95 per cent of average).