22nd August 2018
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Snow covered the isles in coldest January since 1987, according to weather figures

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The first week of January in Shetland was cold and cyclonic, with low pressure over the North Sea or eastern UK bringing mainly north-easterly winds.

The 8th and 9th were briefly very cold anticyclonic, as high pressure drifted across northern Scotland into Scandinavia. The 10th to the 22nd saw frequent strong south to south-easterly winds, as Shetland became the battle-ground between milder Atlantic air and the cold continental air circulating around an intense anticyclone centred over Western Russia.

The 23rd to 25th was quieter, as a ridge extended over the Northern Isles. From the 26th to 31st strong cyclonic northerlies brought a return of winter.

Overall winds were predomin­antly (75 per cent) between south-east and north in direction.

Across Scotland – as well as the UK as a whole – it was provisionally the coldest January since 1987. For Lerwick this was also the coldest January since the 2.4°C mean of 1987, though well short of earlier January means: 1.6°C in 1984; 0.8°C in 1979; and 0.5°C in 1959.

Snow, which had lain since 18th December, still covered the ground to a depth of seven centimetres at the beginning of January.

On the 1st, with low pressure to the east of Shetland slipping south into the North Sea, a strong to gale-force north to north-easterly wind brought cloudy conditions with further scattered wintry showers.

As the low continued south into the Low Countries on the 2nd, pressure built to the north-west and north-easterly winds brought further wintry showers. These became more frequent and turned more readily to snow later, as winds backed north­erly behind a cold front sinking south over the Northern Isles.

With low pressure over Scan­dinavia and the East Greenland anti­cyclone intensifying, cold northerly winds brought further heavy and prolonged snow showers on the 3rd and 4th.

High pressure – slipping south over Iceland – extended a ridge into the Norwegian Sea on the 5th. The resulting “squeeze” between this and a shallow low over the North Sea, gave strong to locally gale-force north-easterly winds, with gusts to over 50mph bringing “bliz­zard-like” conditions at times in heavy showers and blowing snow.

Between the 5th and 8th there was 10cm of snow at the Lerwick Observatory, probably deeper else­where, with significant drifts in the country areas.

By the 6th, high pressure had slipped south to a position west of the British Isles and, as pressure also built over northern Scotland, wintry showers mainly died out, skies cleared and winds fell light and variable.

A ridge of high pressure brought fine days with a moderate or light east to north-easterly wind on the 7th and 8th. Apart from an isolated wintry shower it was mostly dry, with sunny spells by day and clear intervals at night.

It remained cold or very cold, with daytime temperatures a degree or so above freezing, but falling to between -5° and -6°C overnight, with snow-surface temperatures down to -11.3°C at the observatory.

While pressure fell across south­ern Britain on the 9th – as the main centre of high pressure transferred east into southern Scandinavia – a ridge maintained relatively settled conditions over northern Scotland. After a bright start cloud thickened later, bringing a few wintry showers as south-easterly winds freshened.

On the 10th the Northern Isles remained under the influence of high pressure, extending from Ice­land across southern Scandinavia to east of the Baltic, resulting in a sunny day but with a cold easterly breeze.

Though the 11th remained mainly sunny, easterly winds veered south-easterly and strengthened, as the anticyclone over southern Scandin­avia weakened a little and a deep Atlantic depression swung in to­wards Ireland. Temperatures were a degree or so milder, and a thaw of the lying snow began.

Pressure remained low and comp­lex across the north-east Atlantic on the 12th, though an anticyclone – slow-moving to the north-east of Shetland – while maintaining a fresh to strong south-easterly wind, also gave a mainly dry day with some brighter spells.

The 13th was rather cloudier, with strong south-easterly winds as fronts approached from the west. This, together with some mainly light and patchy rain or drizzle, finally reduced to less than 50 per cent the snow cover that had persisted for 24 days.

Strong south-easterly winds and outbreaks of rain – preceded by sleet – affected the Northern Isles on the 14th, as high pressure over Scan­dinavia moved east into Russia and a deepening Icelandic depression pushed fronts east towards Shetland.

On the 15th and 16th an intense anticyclone over Western Russia extended its influence as far west as the Norwegian coast, holding fronts close to Shetland and bringing cloudy conditions with outbreaks of heavy rain or drizzle, accompanied by strong to gale or severe gale south to south-easterly winds, gusting to almost 70mph.

Drier and brighter conditions followed on the 17th as fronts cleared east and strong south-east­erly winds became moderate to fresh south-south-westerly. Mild south-west to westerly winds brought a mainly dry day with sunny periods on the 18th.

The 19th was also mostly dry but, after a bright start, cloud thickened later as a trailing warm front approached from the west. Again, the strong anticyclone over north-west Russia – its influence extending to north-east Scotland – kept Atlantic fronts to the west on the 20th. How­ever, as strong south-easterly winds blew from a cold continent across a relatively mild North Sea, it was a cloudy, raw day with wintry showers developing later.

Little changed during the next two days: an intense anticyclone over western Russia maintained the raw, strong to near gale-force south-easterly winds, bringing cloudy conditions with further mainly light wintry showers on the 21st.

Outbreaks of occasionally heavy rain or drizzle with strong to gale-force south to south-easterly winds followed on the 22nd, as Atlantic fronts made slow progress eastwards.

Strong to gale south or south-easterly winds eased moderate on the 23rd as a front finally moved east over Shetland. However, the day remained cloudy with patchy light rain or drizzle, as the front – a weak affair by now – was pushed back west, as the Russian high drifted towards the Baltic.

With a ridge extending west from the Baltic high, moderate or fresh south-easterly winds brought cloudy but mostly dry days on the 24th and 25th.

As the ridge declined south overnight and a warm front trailed east over northern Scotland, strong to gale-force south-westerly winds brought mild, damp conditions with outbreaks of rain or drizzle to the Northern Isles for the 26th and start of the 27th.

During the day an anticyclone – building strongly to the southwest of the UK – extended into mid-Atlantic, and strong winds in the north veered westerly and later north-west to northerly. Colder, clearer air then flooded south behind a cold front sinking into the Scottish mainland. By evening showers had turned to snow in Shetland.

With a depression moving south over the Baltic and pressure high to the west, cold north to north-west­erly winds brought wintry showers on the 28th. A trough of low pressure – developing along the Norwegian coast – maintained the flow south of frequent and at times heavy and prolonged snow showers on the 29th.

The 30th was a somewhat bright­er day and the showers less frequent, with strong northerly winds easing and backing north-westerly as high pressure to the west began to sink south. Further heavy snow showers followed on the 31st as a frontal trough slipped south across Shetland.

Dave Wheeler