Fair Isle Weather - January 1999

A mild (+0.7°C) month with rainfall a little below normal (86.9%) but also quite sunny (134.3%).

Much of the mildness of January was due, not to high maxima but to the lack of low minima. While the mean daily maximum temperature for the month was just +0.4° Celsius higher than average (5.9° Celsius), the mean daily minimum was +0.9° Celsius higher than normal (3.2° Celsius). The lack of cooling was even more marked at Lerwick where the mean minimum of 2.8° Celsius was +1.6° Celsius above normal. This is all the more surprisingly considering that, as indicated by increased hours of sunshine, cloud amounts were lower than usual
- which should have led to marked overnight cooling. And why, when the predominantly SW’ly winds should have produced cloudier conditions, was January sunnier than normal!

The month began mild and windy with a deep low to the west of Ireland and a strong SE’ly airflow across the Northern Isles. As the low drifted northwards, winds increased to near gale force for a time before easing and veering SW’ly later as the low continued northwards and filled.

After the 6th, as a complex area of low pressure transferred north-east across England, moderate N to NE’ly winds set in over northeast Scotland bringing colder conditions and wintry showers – leading to a thin snow cover by the morning of the 10th.

By the 11th a deep Atlantic low, moving north-east towards south-west Iceland, was pushing fronts east across Shetland and bringing milder SW’ly winds to the area. The next couple of days saw gale to severe SE’ly gales as the progress eastwards of Atlantic frontal troughs was blocked by high pressure developing over Scandinavia. The frontal troughs cleared east early on the 13th, the wind veering SW’ly and easing.

SW’ly winds then increased, with severe gales for the south-west and west of Scotland, as a deep and vigorous Atlantic low, moving northeast towards Faeroe, drove its warm front east across the country. By midday on the 15th, the low had deepened to 926 mb with S’ly winds increasing to gale force across the Northern Isles ahead of the warm front.

As the filling low moved away to become slow-moving close to east Iceland on the 16th, a strong to gale force showery SW’ly airflow brought heavy showers of hail and sleet. S to SW’ly gales persisted through to the 18th, when a weak ridge of high pressure brought a brief respite with moderate W’ly winds.

Another Atlantic low, tracking northeast, brought SW’ly gales, these easing and veering W’ly by the 21st as the low moved away into the Norwegian Sea. A small wave low running north-east along a slow-moving occlusion resulted in a wet day on the 24th.

On the 25th, as a shallow low moved east across the UK and on into southern Scandinavia, a cooler NE’ly airflow was introduced across Scotland for the next few days.

A slack area of high pressure, building over Shetland, then continued the bright but showery conditions until an anticyclone, developing over the south of England after the 29th, introduced a mild and cloudy SW’ly airflow over northern Scotland. Atlantic depressions, tracking through the Iceland area, dragged their fronts across the Northern Isles giving a dull and misty end to the month.

Daily Data
Weather Diary

 

1999

Day

1974-98

1999

Day

1974-98

Mean Maximum Temperature

6.3

5.9

Highest Max temp

8.7

30

11.1

Mean Minimum Temperature

4.1

3.2

Lowest Min temp

0.2

27

-4.5

Mean Sea Temperature

8.5

7.2

Lowest grass minimum

-2.9

11

-10.2

30 cm Earth temperature

4.9

4.7

Days with ground frost

6

10.9

100cm Earth temperature

5.6

5.6

Days with air frost

0

4.5

Total Rainfall (mm)

86.7

99.3

Days with snow/sleet

11

13.2

Wettest Day (mm)

10.5

23

15.1

Days with snow cover at 09hr

1

4.6

Rain Days (> 0.1mm)

27

25.4

Days with hail

12

13.9

Wet Days (> 0.9mm)

20

19.1

Days with fog during 24hrs

1

3.3

Total sunshine, hrs

36.0

27.2

Days with fog at 09hrs

0

0.4

Sunniest day, hrs

4.5

8

4.4

Days with NIL sun

11

14.2

Mean wind speed, kts

17.4

20.9

Days with gale

9

11.3

Maximum gust, kts

59

12

74.1

Days with thunder

0

1.0

Mean Sea Level pressure

998.0

1005.6

Days with aurora

2

3.4

Wind Direction (%) North

9.7

10.3

Wind Direction (%) S. West

29.0

17.9

at 09 hr N. East

0.0

5.1

at 09 hr West

16.1

18.5

East

0.0

7.4

N. West

9.7

9.8

S. East

12.9

11.6

South

22.6

19.2

CALM

0.0

1.1

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Last edited on 21 February, 1999   Dave Wheeler weatherman@zetnet.co.uk
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