16th October 2018
Established 1872. Online since 1996.

Coldest October for 50 years in some parts of isles

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WITH low pressure usually not far from, and often to the north of Shetland, a mainly westerly cyclonic airflow gave a very changeable, unsettled and cool month.

Like the rest of Scotland, while Shetland experienced rainfall significantly above average, it was at the same time reasonably sunny. Helped no doubt by the two outbreaks of – for October – unusually cold Arctic air, the month was also the coolest since 2003.

While the first snowfall on the 4th was possibly one of the earliest recorded (certainly since the snow-cover of 13th October 1957), it was local to Shetland. The second, on the 28th, saw substantial snowfall, possibly the heaviest and most widespread such event in lowland Britain since 1880, with some places seeing their coldest October day for 50 years.

With a depression off south-west Norway, the 1st was a bright day with scattered showers and a cool north-westerly wind. As the low moved east into Scandinavia during the 2nd and cold northerly winds strengthened to gale- force and showers became more frequent.

As pressure built to the west of Scotland on the 3rd, air of Arctic origin flowed south and the showers turned wintry. However, gales did ease – at least for a time – as a ridge sank south over the British Isles.

A complex, though shallow, area of low pressure then developed across the north-east Atlantic and southern Norwegian Sea, The 4th was a cold, wet and windy day. A marked cold front, the boundary between the unseasonably cold air to the north and milder air to the south moved down across Shetland during the morning. Though areas to the south of it had mainly rain or sleet, parts of West and North Mainland – just in the colder air – saw the rain turn readily to snow, giving some areas an unusually early October snow-cover. By evening, westerly to north-westerly gales were again developing across the isles.

Milder conditions followed, gales eased and showers died out on the 5th as a deep low, tracking east to the north of Shetland, moved away north along the Norwegian coast.

South-easterly winds freshened on the 6th, ahead of fronts which brought outbreaks of mainly light, showery rain later in the day. However, with low pressure over Iceland, a moist and mild south-easterly airflow produced very heavy rain accompanied by thunder and misty conditions on the 7th.

The thundery trough cleared north overnight, to leave the Northern Isles with a much bright­er, drier day and fresh westerly winds on the 8th. As low pressure moved east into Scandinavia, a weak ridge followed from the west overnight.

The 9th started dry and bright as the ridge declined, but turned wet with strengthening southerly winds as a very deep Atlantic depression drove an occluded front east over the Northern Isles.

As the filling low tracking slowly away over Iceland, the 10th and 11th were drier, brighter days with outbreaks of mostly light, showery rain and very mild, strong to gale-force south-west to westerly winds.

There were further outbreaks of rain on the 12th as the next Atlantic depression pushed a front east. This cleared Shetland early on the 13th, with strong south-west to westerly winds bringing frequent showers. A ridge of high pressure, moving in from the west, killed off the showers and brought lighter winds to leave a mostly dry, sunny day on the 14th.

A cold front, associated with a depression moving east to the south of Iceland, crossed Shetland on the 15th bringing some rain, with cooler and showery conditions following from the north-west.

The fresh to strong south-west to westerly winds – gusting to over 50mph – veered to a showery west to north-westerly direction on the 16th, as the deep depression moved east to the north of Shetland.

Winds eased overnight as a ridge crossed from the west, then strengthened south-westerly on the 17th as a depression, tracking north-east over Iceland, pushed a warm front across northern Scot­land, bringing a little rain.

A more active cold front fol­lowed overnight, leaving the area in a strong and showery westerly airflow. This eased and backed south-westerly later on the 18th, bringing a mostly dry night as the filling low moved away and a weak ridge followed from the west.

The next deep depression pushed more rain-bearing fronts east on the 19th, with south-westerly gales developing as it moved towards Faroe.

The 20th and 21st were cold days with frequent showers, the heavier ones wintry with sleet and hail. Strong to gale-force winds – gusting to over 60mph – veered westerly as the filling low moved away over the Norwegian Sea.

The 22nd was a drier, milder day with strong winds backing south-westerly later as more fronts moved in off the Atlantic. There were outbreaks of rain on the 23rd, with strong to gale south to south-westerly winds gusting to 81mph on Fair Isle, as fronts moved slowly east over the Northern Isles.

With a deep depression slow-moving just north-east of Iceland, the 24th was quite a cool day with heavy, wintry showers, as the strong to gale-force south-westerly winds, despite their direction, had an Arctic origin. Some of the showers were also accompanied by thunder. A front, pushed north-east by a deep and vigorous low running quickly north past north-west Scot­land, brought heavy rain and severe gale-force Southerly winds north across Shetland early on the 25th. During the afternoon, as the front passed, winds increased storm Force 10 to violent storm Force 11 and for a short while hurricane Force 12, with a 10-minute mean wind speed of 74mph.

There were gusts up to 93mph at Lerwick and 89mph on Fair Isle; this is probably a new October wind-speed record for Shetland. Later in the day, the rain cleared to blustery, heavy and occasionally thundery showers as gales veered south-westerly.

The showers turned wintry on the 26th as the low moved away into the Norwegian Sea and winds veered westerly. The 27th was another cold day, with showers turning progressively more wintry as strong to gale-force winds veered north-westerly.

With pressure high in mid-Atlantic and low over the Nor­wegian Sea, strong and Arctic north-westerly winds, accompanied by temperatures of around -2° Celsius, brought a bitterly cold start to the 28th. A small but significant low moved south just to the east of Shetland, bringing another period of unseasonably early snow, accompanied by strong winds. Gusts of over 60 mph occurred in places across Shetland.

One is left wondering (had this happened a few months further into winter, when sea temperatures would be some 4° Celsius lower than the current 11° Celsius) just how much snow would have occurred.

In the event heavy snow – as in the earlier fall – soon turned to rain, but not before some places had seen yet another October snow-cover of several centimetres.

With the temperature ranging from a low of -3° to a high of only +3° Celsius, this was probably the coldest October day since 1964, when the temperature fell to -3.3° Celsius.

With a filling low off south-west Norway, fresh north to north-easterly winds brought scattered showers, a few wintry, to Shetland on the 29th.

The cold winds persisted through the 30th, although the showers gradually died out as an anticyclone, developing south of Iceland, extended a ridge of high pressure north-east across Faeroe into the Norwegian Sea.

The 31st was a bright, mostly dry and cool day, with the north to north-easterly winds easing as the ridge toppled south-east across Shetland into northern Scotland.

Initial Statistical details for Scotland as a whole (1961-1990 average) for October) Mean temperature – 7.3°C (0.8°C below average). Coldest October since 2003.

Rainfall – 242.2 mm (152% of average). Fourth wettest October since 1954.

Sunshine – 86.5 hours (117% of average).

OCTOBER STATISTICS RECORDED AT LERWICK OBSERVATORY

Averages – 1971  :  2000

Mean maximum temperature – 9.7°C  :  10.1°C
Mean minimum temperature – 5.9°C  :  6.2°C

Daily mean temperature – 7.6°C  :  8.1°C

Mean sea-level pressure – 1000.1 hPa (mb)  :  1008.0 hPa (mb)

Total rainfall – 179.8 mm  :  131.9 mm

Wet days => 1 mm – 26 days  :  19.4 days

Sunshine (electronic sensor) – 69.3 hours  :  65.4 hours

Air frosts – 1 day  : 0.5days

Ground frosts – 6 days  :  5.2 days

Snow/sleet – 4 days  :  2 days

Days with gale – 6 days  :  4 days

Maximum daily mean temp: 12.0°C on 10th
Minimum daily mean temp: 0.5°C on 28th
Highest maximum: 14.7°C on 10th

Lowest day maximum: 3.0°C on 28th
Highest night minimum: 10.6°C on 10th
Lowest minimum:  -3.0°C on 28th
Lowest grass minimum:  -4.9°C on 28th

Wettest day: 30.2 mm on 7th
Sunniest day: 6.1 hours on 14th