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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 SWly 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 SEly airflow across the Northern Isles. As the low drifted northwards, winds increased to near gale force for a time before easing and veering SWly 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 NEly 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 SWly winds to the area. The next couple of days saw gale to severe SEly 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 SWly and easing. SWly 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 Sly 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 SWly airflow brought heavy showers of hail and sleet. S to SWly gales persisted through to the 18th, when a weak ridge of high pressure brought a brief respite with moderate Wly winds. Another Atlantic low, tracking northeast, brought SWly gales, these easing and veering Wly 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 NEly 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 SWly 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.
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