April 1997

On Fair Isle the month was dull and wet with near average temperatures. While rainfall was well above average (149.6%) this was as a result of a few wet days - rather than a persistently wet month.

The month began, cold, unsettled and windy with several wet days and gales on the 2nd and 3rd in a burst of Arctic air. A change to mainly anticyclonic conditions then occurred, giving a relatively settled and mild period with little in the way of rainfall - although on the 10th Fair Isle was the wettest place in the UK with a mere 2.2 mm of rain.

Though cool the 14th, with over 12 hours of bright sunshine, was a particularly sunny day. After mid-month it again turned unsettled and decidedly cool with snow, sleet and hail. On the 19th, together with Lerwick, Fair Isle was the coldest place in the UK - reporting a daytime maximum temperature of 5.9° Celsius. On the 22nd our maximum temperature was only 3.3° Celsius, but Sella Ness was the coldest place in the UK with a maximum of only 2.6° Celsius!

On the 23rd and 24th the most vigorous depression of the month crossed Scotland - giving Fair Isle its wettest day of the month on the 23rd (21.6 mm) and a NE'ly gale on the 24th.

Weather Diary - April 1997

1. Cloudy with rain turning to showers overnight - the WSW'ly F5-6 increasing F6-7 by morning. Showers becoming scattered during the morning, but becoming rather blustery during the afternoon with a gust to 48 kt at 1618z. Visibility 15 km to 20 km.
2. Overnight rain and drizzle - moderate at times - continuing through the morning and becoming moderate rain during the afternoon. Visibility falling to 3000 m by morning, improving to 08 km to 15 km for a time late morning. The wind, WSW'ly F6-7 increasing gale F8 1400-1410 UTC and 1535-1545 UTC. Low overcast clearing to medium level at 1800 UTC, with a general clearance from the NW after 1830 UTC - the wind then veering W'ly and easing F5-6. Sky virtually cloudless by midnight with an exceptionally brilliant Hale-Bopp comet - two tails visible (the second very faint). A mild day, but becoming cooler during the evening.
3. Variable amounts of cloud and wintry showers of rain, snow and small hail overnight - the W'ly F6 wind veering N'ly and easing F5. By 0800 UTC the wind had backed NW'ly. Dry, though cloudy, until late morning when the showers that had been observed building to the west finally arrived at the isle. Frequent wintry showers of rain, small hail and snow during the afternoon. With the arrival of the showers the wind, becoming quite gusty (64 kt at 1630 UTC.) increased F6-7 and to gale F8 at 1630-1640 UTC and 1707-1804 UTC. A drier evening with scattered wintry showers and a F6-7 NW to N'ly wind. At 2100 UTC there was a little thawing snow and ice on the ground. Visibility during the day was generally 20 km to 25 km, falling to 1500 m in the heavier sleety showers. Later in the evening the ground began to dry out as drier air arrived.
4. Well-broken cloud at times leading to a ground and air frost. Showers of snow, snow pellets and small hail early. The F6 NW'ly wind had eased F4 by 0600 UTC. A bright start to the day as the low cloud dispersed, but no recorded sunshine due to the thickening high cloud. By midday the wind had become a light S'ly. It remained cold during the morning with good visibility of 40 km in the dry air (temperature 2° Celsius and dew point down to -7° Celsius). As the medium level cloud continued to thicken snow began to fall after 1600 UTC. There was a light dusting by 1800 UTC with a significant cover above 250 ft. With the arrival of the snow the visibility was reduced and, as the snow became moderate by 1800 UTC the visibility fell to 1000 m. During the afternoon the wind had swung into the SE and steadily increased to be F6 by 1800 UTC. During the evening the snow gradually turned to rain and drizzle as the temperature slowly rose - to 4.5° Celsius by midnight. 1315 UTC: Sea temperature 7.4° Celsius.
5. By 0600 UTC the early F6 SE'ly wind had veered NW'ly F5 with a clearance of the rain and drizzle. The poor visibility had also improved to 25 km to 40 km. The wind then quickly veered NE'ly, increasing F7 at times. However it remained cloudy with further patchy light drizzle during the morning, this becoming showery by midday as the cloud began to break - with an isolated cumulonimbus cloud visible. There were further showers during the afternoon - becoming wintry with flakes of wet snow by 1700 UTC. By this time the cloud had become well broken with the NE'ly wind easing F3 during the afternoon - later backing NNE'ly. Temperatures had fallen from an early 7° or 8° Celsius to 1° Celsius by the end of the evening as the cloud became well broken and the wintry showers died out.
6. A light F2-3 NE'ly wind and well-broken cloud resulted in a ground frost - the ground frozen by 0600 UTC - and the air temperature falling to near freezing. Cloud amounts continued variable through the morning, with long sunny spells despite the increasing high cloud. At the same time the light wind veered E'ly. Cloud amounts increased through the afternoon with a SE'ly wind gradually picking up. The temperature steadily rose during the afternoon. Thickening medium level cloud during the evening brought rain and drizzle by 2100 UTC - the earlier SE'ly wind backing SSE'ly and increasing F6 by this time. With the onset of the precipitation the early visibility of 40 km fell to 10 km and to 2000 m by midnight in moderate drizzle, low stratus and a temperature rising to 6° Celsius.
7. Overnight drizzle poor visibility and low stratus clearing by 0600 UTC with the F7 SSE'ly wind veering WSW'ly and easing F5. The visibility improving to 8 km by the same time. A dry, cloudy morning with the visibility improving to 15 km. Some outbreaks of mainly light drizzle or rain and drizzle during the afternoon - the visibility falling to 3000 m for a time. The WSW'ly wind continued, but eased F4, occasionally F5. Further periods of rain and drizzle during the early part of the evening. By midnight the wind had backed SW'ly and eased F3. A mild day.
8. A cloudy, mild day. Dry for the most part then a period of mainly light rain during the first part of the evening. Winds were F4 S to SSW'ly, veering WNW'ly at 2035 UTC with the clearance of the rain and increasing F4-5. Visibility was good at 20 km, but falling to 10 km to 15 km in the precipitation. 0600 UTC: Sea temperature 8.0° Celsius.
9. A dry night, very little low cloud but extensive medium level cloud - this thinning to high cloud during the morning. Visibility was good at 20 km. Showers developed during the afternoon, the F4-5 W'S to W'ly wind increasing F5-6. The evening was overcast with rain and drizzle, low stratus and 1500m to 5000 m visibility.
10. A cloudy day with periods of drizzle and rain and drizzle. During the early afternoon there was a little weak sunshine. Visibility was 06 km to 15 km, but falling to 3000 m in the heavier drizzle - stratus also lowering onto the hill. A F5-7 W to WNW'ly throughout the day, but veering NNW'ly late in the evening. Fair Isle wettest place in the UK (09-09 UTC) with 2.2 mm.
11. Becoming brighter, drier and cooler overnight apart from an occasional and very light 'drizzly' shower. A dry day with sunny spells. The F6-7 NNW'ly wind, gusting to 54 kt at 0136 UTC, gradually moderated during the morning to be F4 by early afternoon. Visibility 20 km to 25 km. Anemometer re-calibration. 2359 UTC: A bright aurora (?) glow observed through a small gap in an otherwise overcast sky.
12. A generally cloudy day with drizzle patches, bringing the low stratus down to almost station level at times. Visibility varying between 5000 m and 20 km, but down to 800 m in low stratus briefly at midday. The wind a F3-4 WSW to WNW'ly in the morning, increasing F4 WNW'ly after midday. The stratus lifting from time to time with a little weak sunshine during the afternoon.
13. A dull, misty day with extensive low stratus. Fog from 0800 UTC as the stratus base lowered to station level, becoming thick by 1035 UTC and dense - with sky obscured - by midday with 80 m visibility. As the South Lighthouse foghorn was sounding it is likely that the 'low cloud' was in fact sea fog for a time. The persistent overnight drizzle or rain and drizzle becoming lighter and patchy during the late morning. The fog thinned to mist later in the afternoon with the cloudbase lifting to several hundred feet. Becoming drier and clearer during the evening with the visibility improving to 15 km as the F4-5 W'ly wind veered F4 NW'W.
14. An unexpectedly sunny day - the low cloud of yesterday dispersing overnight to give a fine, sunny morning. Only small amounts of cloud during the late morning and afternoon, but an extensive stratocumulus cloud-sheet spreading in by evening. A cool day with a fresh F4-5 NW'ly wind veering NNW to N'ly during the morning - the visibility improving to 40 km.
15. A cool night with well-broken cloud by dawn, the F3-4 N'ly wind having backed NW and eased F2-3. A sunny start to the morning then a stratocumulus sheet spreading in by 0900 UTC. The wind backing W F2-3 by this time. After midday the cloudbase lowered quickly, with the visibility falling from 40 km to 15 km. Light drizzle began at 1310 UTC - the visibility falling to 2500 m with stratus down to 100 ft. During the afternoon the W'ly wind increased F4-5. The evening remained cloudy but did become clearer as the drizzle turned patchy and the cloudbase lifted a little.
16. A generally cloudy night with a little light drizzle and a F3-4 W to WNW'ly wind. Misty with a little low stratus and visibility 8 km, falling to 5000 m by 0800 UTC. A dry, but misty morning - the visibility 15 km to 3500 m. Dry during the morning and afternoon, with a little weak sunshine after midday. Cloud then thickening and lowering with drizzle by 1700 UTC. The drizzle, moderate at times, continued into the evening with the wind becoming a light and variable in direction - mostly between NW and NE.
17. A cloudy night with some early light drizzle and light NNW to NNE'ly winds. A mostly cloudy morning with a light N'ly wind, but the cloud then becoming well broken to give a lovely spring-like afternoon. In the afternoon warmth cumulus clouds developed over Fair Isle - slowly drifting away on a F3 NW'ly wind with the next cloud building over the isle. Becoming cloudy during the evening with the F3 wind backing W'ly. Some light drizzle during the late evening. The early visibility of 12 km to 15 km improving to 30 km during the afternoon, then falling to 6 km in the late evening drizzle.
18. A cloudy night with drizzle, moderate at times and a F3 W'N' wind veering NE'E and increasing F5 at 0515 UTC. A brighter morning with the visibility improving from 10 km to 30 km as the wind veered F4 E'N. There were occasional light rain showers during the morning. A dry afternoon with a few sunny spells developing as the wind backed NE'ly - the visibility improving to 50 km. A mild start to the day, but becoming cooler during the day, and quite chilly by late evening as the temperature fell to 3° Celsius (Td -6° Celsius) with a F4-5 N'ly wind.
19. A dry, though mostly cloudy night with a F4 N'ly wind. Continuing dry during the day - apart from one light rain and small hail shower at midday. Remaining mostly cloudy, but a brief flash of sunlight during the afternoon, and becoming sunny after 1600 UTC as the cloud quickly dispersed. A day of excellent visibility - due to the dry air - the air temperature around 4° to 5° Celsius and Td down to -6° Celsius (RH 48%). Wind veering NNE'ly and easing F3 mid-afternoon, later backing NNW'ly, then easing F1-2 during the evening. A fine evening, but with a thin (perlucidus) stratocumulus cloud sheet later. Aurora was reported from Shetland, but this was not visible from Fair Isle due to the bright moonlight and cloud-cover. Slight ground frost by late evening. With a maximum of 5.9° Celsius both Lerwick and Fair Isle reported the UK's lowest day maximum temperature.
20. Dry and mostly cloudy overnight, the light W to NW'ly wind increasing F4 by 0600 UTC. A bright start to the day with some sunshine as the stratocumulus cloud sheet cleared to 2 okta 0730-0830 UTC. Still cool with dry air and excellent visibility of 50 km. At 1045 UTC an aircraft flying between Kirkwall (Orkney) and Tingwall (Shetland) reported the cloud tops at FL 42 (4200 ft approx.). During the morning the wind backed WSW'ly, increasing F5 through the afternoon and F5-6 by evening. Light rain commenced at 2030 UTC, by which time the visibility had fallen to 20 km, with a wind veer from 250° to 330° at 2100 UTC. The rain, moderate at times, had become intermittent by midnight.
21. A mostly cloudy night with wintry showers of small hail, rain and snow developing as the wind veered NW'ly F6. During the morning the wintry showers died out, but it continued windy with the NW'ly wind increasing F7. Dry for a time around midday, but then further wintry showers developing - with one of snow between 1700-1800 UTC. During the afternoon the wind eased F5-6, veering N'ly by 1600 UTC. Visibility was mostly good at 20 km, but fell to as low as 4000 m in the heavier showers. Though remaining cloudy the showers had died out by midnight. Becoming colder during the evening with the daytime air temperature of around 4° Celsius falling to just under 2° Celsius.
22. Cloudy overnight with a F4-5 NNW'ly wind and frequent but very light snow showers. Visibility good at 25 km to 35 km - not affected by the very light snow - with dry air. Temperature 1° to 2° Celsius and Td -4° to -5° Celsius. Lerwick, at 0600 UTC, reported a Td of -11° Celsius. The day continued cloudy with the wind slowly easing F4 and backing NW'ly. Occasional snowflakes continued to drift on the wind until mid-afternoon. During the evening the wind backed SW'ly, easing F1-2 by midnight - at which point the observer was surprised to find it gently snowing with 1 cm of lying snow and the air temperature just a little above freezing.
23. The light snow hard turned to rain and snow by 0600 UTC as the temperature rose from near freezing to 1.5° Celsius - still with 1 cm of snow cover. The wind, virtually calm at first, slowly increased and veered to be F3 E'ly by 0600 UTC, and F5 by midday. By 0900 UTC there was no lying snow left. An hour later all the snow had also gone from Ward Hill (712 ft). The rain, mostly light, continued through the morning - with a hint of brightness to the north-east as the visibility improved to 20 km. The rain became heavier through the afternoon, with the visibility falling to 10 km. At 1510 UTC the F5 E'ly wind veered SE'ly, but then gradually backed E'ly after 1800 UTC and easing F1 after 2100 UTC. At 2130 UTC the wind quickly backed WSW'ly and increased F5. The evening was decidedly wet - with many large pools of standing water. By 2100 UTC the moderate/heavy rain had become moderate drizzle - with the visibility falling to 3000 m as the cloud base lowered to 100 ft.
24. A cloudy and wet night with early rain and drizzle turning to showers sometime before 0500 UTC. The wind, F5 WSW'ly at first, easing F4-5 and veering W'N then at 0525 UTC veering NNE'ly and increasing F7 by 0530 UTC. The wind then veered further to NE'ly, increasing gale F8 0610-0810 UTC. The showers were frequent, but light, dying out by 0900 UTC - after which it became quite sunny. Increasing cloud brought further showers from early afternoon until the middle of the evening. During the afternoon the wind slowly backed and eased - to be N'ly F5 by 1800 UTC. A clear end to the day with well-broken cloud by midnight when a weak aurora glow was observed to the north. A cool day with the visibility around 25 km.
25. Apart from an early small hail and rain shower it was a dry and sunny day with very little cloud. The wind, a cool F4 NNE'ly at first, slowly veered to be E'ly by midday. Late in the morning it also eased F2-3. Visibility improved to 60 km during the afternoon in the dry air (RH 50-55%, and 49% at 1800 UTC, Td down to -6° Celsius). By evening the wind had veered ESE'ly.
26. A cloudy, dry day with a cool F5 SE'ly wind. The air was quite dry at first, temperature around 4° or 5° Celsius and a Td around -2° Celsius (RH about 60 %). During the day the Td rose to around 0° Celsius. Visibility was good at 40 km.
27. A cloudy, dry night - the cloudbase gradually lowering, with extensive low stratus by 0600 UTC and the visibility falling to 3500 m by 0900 UTC. A dry but hazy day, with the stratus base lifting a little to 800 feet around midday. Later the cloudbase again lowered, with patchy drizzle by late afternoon - the visibility falling to 2000 m. The wind throughout the period was F4-5 SSE to SE'ly. A milder day.
28. A damp, misty night with outbreaks of drizzle, extensive low stratus just above station level and patchy drizzle and a F4 SE'ly wind. Visibility fell below 1000 m at 10005, the fog soon becoming thick with sky obscured. Some rain and drizzle at times during the morning, becoming dry by midday. During the afternoon the SE'ly wind eased F3. The thick fog persisted through the afternoon - temporarily thinning later in the afternoon to 400m, then becoming dense during the evening with a visibility of 80 m. Rain and drizzle, moderate at times later in the evening.
29. A foggy night with rain and drizzle and a F3 SE'ly wind. By 0600 UTC the fog had lifted to low stratus just above station level and a visibility of 1200 m. Fog returned by 0700 UTC as the cloudbase again fell to below station level. As the South Lighthouse foghorn was sounding sky obscured was reported. Later in the morning as the visibility improved to 800 m the sun became faintly visible. Soon after 0700 UTC the wind veered SW'ly. By 1100 UTC fog patches were being reported - the wind now WSW'ly. The visibility improved to 2500 m briefly in the early afternoon, but the fog soon returned. Outbreaks of very light drizzle continued through the day. By late afternoon the wind was W'ly at F3-4. Soon after 1800 UTC the visibility improved to 4000 m as the fog lifted into low stratus. A dry, cloudy evening with the visibility around 10 km.
30. A cloudy day with occasional outbreaks of light rain or drizzle. The visibility improved to 20 km overnight, temporarily falling during precipitation. During the morning the F4 SW to WSW'ly wind backed SSW'ly and increased F5 but veered SW'ly after midday. At 1445 UTC the wind increased F5-6 and veered WSW'ly. The drizzle became more persistent with stratus low on the Hill and the visibility steadily falling. By 1800 UTC the visibility had fallen to <1000 m. During the latter part of the evening the fog cleared - the stratus lifting to 800 ft. The drizzle ceased shortly before midnight, the visibility then 15 km.

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Last edited on 09 January, 1999   Dave Wheeler weatherman@zetnet.co.uk
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