18th August 2018
Established 1872. Online since 1996.

November was cool, cloudy and windy

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By DAVE WHEELER

DURING November the Icelandic low was deeper and displaced towards the Norwegian Sea, while at the same time the Azores anticyclone was slightly further north than its usual position.

As a result – with just a couple of exceptions – low pressure dom­inated the month’s weather patterns, bringing a cyclonic west to north-westerly airflow across Shetland for much of the time.

It was probably the most “northerly type” November for the past four decades but, despite this, the month’s mean temperature was still above the 1971-2000 average.

Early in the month a brief anti­cyclonic spell occurred, as a small high drifted north-east over Shet­land. Shortly after mid-month, a marked outbreak of cold Arctic air brought a snowy period, as low pressure moved east and the rather persistent anticyclone in mid-Atlantic ridged north.

On the 1st, though a ridge of high pressure lay across much of Scotland, Shetland – in the south-westerly airflow on its northern edge – saw mild and cloudy con­ditions. Weak fronts, associated with low pressure to the north, brought periods of mainly light rain.

The 2nd – still rather cloudy – was mostly dry and somewhat brighter, as lighter winds backed southerly ahead of more fronts bringing further outbreaks of rather persistent rain or drizzle, ac­companied by misty conditions and hill fog, on the 3rd.

However, as an anticyclone – developing over northern Scotland – moved closer to the Northern Isles, easing winds veered northerly, skies cleared and temperatures fell sharply, with a frost developing overnight. After a cold start, the 4th was a fine, sunny day.

The small high then drifted north-east across Shetland into southern Scandinavia, with south-easterly winds freshening on the 5th, bringing cloudy and misty conditions with patchy drizzle.

Winds strengthened further on the 6th, as the intensifying high moved away over the Baltic and an Atlantic frontal trough approached western Scotland. The 7th was a dull and mild day with outbreaks of rain or drizzle and strong south-easterly winds, with the 8th drier and brighter as fronts cleared north and strong winds veered southerly.

A developing low – tracking north to the west of Scotland – brought some early rain followed by scattered showers on the 9th, as an associated front moved across the Northern Isles. With the low slow-moving to the north-west of Scotland, the 10th brought further patchy rain or showers and strong to gale-force southerly winds. There were frequent and sometimes heavy showers on the 11th but, as the filling low drifted east over the north of mainland Scotland, much lighter winds backed north-easterly.

As the filling low moved away over southern Scandinavia and pressure built to the west, a colder Arctic airflow brought sunny spells and scattered showers for the 12th. However, the cold spell was short-lived, with strong to gale-force south-westerly winds bringing much milder and cloudy conditions – together with outbreaks of heavy rain or drizzle – during the follow­ing two days, as the next Icelandic depression pushed fronts east over northern Scotland.

The 15th and 16th were cooler and brighter with showers – some wintry – as the low continued east over the Norwegian Sea. As pressure built to the west, westerly to north-westerly winds increased strong to gale-force. Gusts to 63mph were recorded in Lerwick, 61mph on both Foula and Fair Isle on the 15th and 68mph on Foula early on the 16th.

Winds then eased as a ridge declined south-east over the area early on the 17th, with a fresh south-easterly wind bringing patchy rain or drizzle later in the day, as a low tracked east over northern Scotland. This was followed on the 18th by cooler and showery conditions, accompanied by strong north-westerly winds, as pressure again built to the west.

With a depression over the north of Scandinavia and an anticyclone in mid-Atlantic, strong to gale-force westerly to north-westerly winds continued through the 19th and, after a mild start with temperatures around 11° C, much cooler con­ditions followed by the end of the day.

On the 20th a frontal trough – moving south in a cold Arctic airf­low – saw wintry showers of rain, hail and sleet turning to a long­er period of snow as temperatures continued to fall towards zero. Strong north-westerly winds eased significantly, and many places saw a thin covering of snow by the evening.

On the 21st there were frequent, heavy and prolonged showers of snow with drifting in the strong northerly winds, as temperatures fell to -1° or -2° C.

With temperatures dropping to between -3° and -4° C overnight and struggling to reach 0° C during the day, the 22nd was even colder with further snow showers. Most places had several centimetres of lying snow, with 8cm reported from Fair Isle. However, as northerly winds eased, drifting of the lying snow became less of a problem.

A ridge crossing the Northern Isles was quickly followed on the 23rd by milder temperatures, as a depression slipped south-east from Iceland across Orkney and strengthening south-easterly winds backed north-easterly through the day.

Northerly winds followed on the 24th but, circulating around low pressure to the east, these were not of Arctic origin and so temperatures were not particularly low. As a result, despite some of the frequent and heavy showers being wintry in nature, a steady thawing of the lying snow continued.

The showers died out on the 25th as a ridge toppled across the area and easing winds backed south-westerly. Later in the day, as the next depression moved into the Iceland area, strengthening westerly winds brought cloudy conditions and patchy rain. With pressure remaining low to the north and a front – trailing around the northern flank of an anticyclone – slow-moving close to Shetland, strong to gale-force westerly winds, carrying outbreaks of rain or drizzle across the Isles, continued for the next couple of days.

As a small low moved east to the north of Shetland early on the 27th, a cold front sank south-east into Scotland. This introduced cooler and showery conditions across the Northern Isles, with westerly winds gusting to 65mph early in the day. By evening winds had fallen light and variable as a slack area of low pressure formed over northern Scotland and the southern Norwegian Sea.

This persisted through the 28th and 29th. On the 30th low pressure moved east and a cold Arctic airflow – sweeping down over Iceland and the north-east Atlantic – gradually extended over Shetland. As it did so, showers turned wintry and north, north-easterly winds increased strong to gale, gusting to 63mph in Lerwick by the end of the day.

Initial Statistical details for Scotland as a whole (1961-1990 average) for November:
Mean Temperature: 4.8°C (0.5°C above average)
Rainfall: 140.3 mm (89 per cent of average).
Sunshine: 52.1 hours (108 per cent of average).

November statistics recorded at Lerwick Observatory

November 2008  :  Averages 1971-2000
Mean maximum temperature 7.4°C  :  7.6°C

Mean minimum temperature 4.1°C  :  3.6°C
Daily mean temperature 5.7°C  :  5.1°C

Mean sea-level pressure 1005.3 hPa (mb)  :  1006.5 hPa (mb)

Total rainfall 118.2mm  :  152.4mm
Wet days > 1mm 24  :  21.5

Sunshine (electronic sensor) 29.6 hours  :  33.0 hours

Air frosts 4 days  :  3.5 days

Ground frosts 13 days  :  10.5 days

Snow/sleet 8 days  :  6.8 days

Days with gale 6 days  :  5.5 days

Maximum daily mean temp 9.6°C on 14th

Minimum daily mean temp -2°C on 22nd

Highest maximum 11.0°C on 14th
Lowest day maximum 0.0°C on 22nd

Lowest minimum -3.6°C on 22nd
Lowest grass minimum -5.7°C on 23rd

Wettest day 13.0mm on 14th

Sunniest day 4.4 hours on 4th

Highest mean hourly wind 39 knots on 27th

Highest gust 57 knots on 27th