A mild (+0.6°C) month though with snow more frequent than usual and rainfall a little above normal (107.9%), but also quite sunny (122.8%).
Fair Isle faired somewhat better than the rest of Shetland where, according to the statistics from Lerwick Observatory, it was a very windy and wet month with 14 gale days - twice the expected number and 22% more rainfall than average. Fair Isle recorded the usual number of gale days (9), although the mean monthly wind speed (20.4 kt) was a little higher than the average (19.5 kt) and just a little more rain than usual.
High pressure over England and low pressure over Iceland resulted in very mild, strong southwesterly winds – with the month’s maximum temperature of 11.3° Celsius occurring before breakfast on the 1st. A depression, tracking east from Iceland into Norway, strengthened the southwesterly winds to gale force for a time on the 2nd. As the low moved into Scandinavia on the 3rd, winds veered into the north to bring a cold spell with frequent and sometimes heavy snow showers – giving most of Shetland several centimetres of lying snow. With the temperature falling to –3.3° Celsius, the 4th was the coldest day of the month on Fair Isle and, by the 5th, there was 5 cm of snow – with drifts to 30 cm locally and 50 to 60 cm further afield.
Pressure then began to build over Iceland and southwest of the British Isles and, as a ridge moved east across the UK, the strong northerly winds gradually eased to become calm and frosty on the 6th and at first on the 7th. A deep depression in mid-Atlantic then drove fronts east across Shetland, bringing a thaw with strong to gale to severe gale force southwesterly winds and periods of rain. A succession of Atlantic lows, tracking northeast through the Iceland area into the Norwegian Sea, maintained the mild conditions with gales alternating between southeast and southwesterly for much of the following week, with periods of rain followed by showers as frontal troughs moved east. Some of the showers were heavy and with hail. A brief respite early on the 11th did produce the sunniest day of the month – but with rain and a southeast gale before the day was out. Southwesterly winds gusted to 63 kt late on the 14th with thunderstorms - particularly dramatic in the early hours - occurring several times on the 15th.
This pattern continued until the 18th when, with pressure low over the north of Scandinavia, a depression tracked east across central areas of the UK pulling down a N’ly airflow behind it as it moved away into the North Sea. Snow showers again developed in the cold N’ly flow, giving a thin snow cover by late on the 20th.
A ridge, moving quickly east across the area gave a calm, frosty night, with the temperature on the snow surface falling to –6.0° Celsius by the morning of the 21st. Another Atlantic low heading towards Iceland drove its fronts east across Shetland on the 22nd with strong southwest to westerly winds and periods of rain. This was then followed by several days of blustery and occasionally thundery showers. On Boxing Day an intense depression tracked quickly northeast across mainland Scotland. This low backed winds over Shetland into the southeast, which then increased to gale force accompanied by heavy rain, resulting in the wettest day of the month for Fair Isle. Shetland, however, escaped the violent southwesterly gale experienced further south over Scotland and northern England.
A barely discernible ridge of high pressure then followed, giving a brief respite before another intense Atlantic low appeared to threaten the British Isles. However this one filled as it became slow-moving to the west of the British Isles – but not before producing gale to severe gale force southeasterly winds with rain and drizzle to end the year.
 | Daily Data |
| Weather Diary |
1998 |
Day |
1974-98 |
1998 |
Day |
1974-98 |
|||
Mean Maximum Temperature |
7.2 |
6.6 |
Highest Max temp |
11.3 |
1 |
11.5 |
||
Mean Minimum Temperature |
4.4 |
4.0 |
Lowest Min temp |
-3.3 |
4 |
-4.5 |
||
Mean Sea Temperature |
9.1 |
8.2 |
Lowest grass minimum |
-6.0 |
21 |
-11.5 |
||
30 cm Earth temperature |
6.0 |
5.8 |
Days with ground frost |
7 |
8.9 |
|||
100cm Earth temperature |
6.7 |
6.8 |
Days with air frost |
4 |
3.1 |
|||
Total Rainfall (mm) |
111.4 |
103.5 |
Days with snow/sleet |
11 |
10.9 |
|||
Wettest Day (mm) |
12.4 |
26 |
14.4 |
Days with snow cover at 09hr |
6 |
3.3 |
||
Rain Days (> 0.1mm) |
27 |
25.5 |
Days with hail |
12 |
12.5 |
|||
Wet Days (> 0.9mm) |
26 |
20.4 |
Days with fog during 24hrs |
3 |
2.4 |
|||
Total sunshine, hrs |
21.4 |
17.6 |
Days with fog at 09hrs |
0 |
0.3 |
|||
Sunniest day, hrs |
3.5 |
11 |
3.5 |
Days with NIL sun |
10 |
15.2 |
||
Mean wind speed, kts |
20.4 |
19.5 |
Days with gale |
9 |
9.0 |
|||
Maximum gust, kts |
63 |
14 |
69.6 |
Days with thunder |
1 |
0.4 |
||
Mean Sea Level pressure |
1005.3 |
1006.3 |
Days with aurora |
4 |
2.6 |
|||
Wind Direction (%) North |
16.1 |
11.9 |
Wind Direction (%) S. West |
38.7 |
16.5 |
|||
at 09 hr N. East |
0.0 |
4.1 |
at 09 hr West |
9.7 |
17.1 |
|||
East |
0.0 |
8.3 |
N. West |
3.2 |
8.7 |
|||
S. East |
12.9 |
12.5 |
||||||
South |
19.4 |
18.7 |
CALM |
0.0 |
2.2 |
Weather Diary - December 1998
Drifts to 30 cm locally, 50-60 cm further afield. 1030 UTC report of waterspout seen by aircrafte (east of Sumburgh?). 1315 UTC a/c requests cruise at 16,000 ft to clear (CB) tops.
1155 UTC grass min reading -2.2° Celsius - lowest since sunset yesterday. 4 okta SC SW half of sky. 1335 UTC air temp 2.0° Celsius, snow surface -0.1° Celsius. Grass min down to -2.2° Celsius. 3 okta SC, some weak sunshine from a low sun.
Gale 2135 - 2145 UTC.
Gale 0030 - 0330, 0655 - 0707, 0830 - 1200 UTC. Mean 40 kt 1025 - 1035 UTC, gust 53 kt at 1022 UTC. Some weak sunshine late morning.
Anemo calibration 1010 - 1200 UTC. Rain and drizzle from 2030 UTC. Gale from 2130 UTC.
Gale csd 0045 UTC, then steady easing and veer. 0540 UTC wind veer 210° to 240° 0540 - 0555 UTC, speed increase 14 kt to 22 kt during same period with gust to 32 kt at 0553 UTC.
Moderate shower of small hail 0900 - 0903 (within rain shower).
Gale from 1852 UTC, increasing F9 2145 UTC with gust to 63 kt at 2150 UTC. Gale F9 to gale F8 at 2225 UTC.
0145 UTC "rolling thunder then big bang followed by a bright flash" reported to DW. Also "quite a lot of lightning seen." Possible more thunder 0400 - 0430 UTC. Gale F8 increased gale F9 at 0145 UTC, easing gale F8 at 0500 UTC and to gale F9 0550 UTC. Squally showers of rain and hail overnight. Severe gale eased gale F8 at 0710 UTC. Gale ceased 1200 UTC. Further slight thunderstorms at 1157, 1742 and 2157 UTC with further squally hail showers during the afternoon, with some wet snow flakes. Strong aurora glow at 2350 UTC.
Showers of rain, rain and snow and small hail overnight. Small hail, rain and snow and snow pellet showers during the afternoon, with more snow showers during the evening. Some snow/hail deposit on the ground (<50%) from 1400 UTC. Thin strip of light visible low to the north at 2350 UTC - probably aurora glow.
Snow showers overnight leading to 1 cm lying snow by 0730 UTC. Further showers of snow and snow pellets during the morning, with visibility falling <1000 m 1115 - 1122 UTC in moderate snow shower. Aurora glow late evening.
Moderate aurora glow visible at 1750 UTC.
2230 UTC wind veer 210° to 270°, rain to showers at about this time.
Showers of rain, rain and snow and small hail overnight. Gale 0650 - 0715, gust 55kt at 0708 UTC. Moderate shower of rain, small hail and rain and snow 1245-1300 UTC. Gale 1307 - 1325 UTC.
Rain and snow showers overnight, plus small hail showers during the morning. Gale from 1840 UTC. 2330 UTC barograph adjusted to correct pressure of 955.0 mb. Gale ceased at 2115 UTC.
Minimum pressure 954.3 mb c. 0100 UTC. 1400 - 1500 UTC moderate shower of rain, small hail, rain and snow.
Grass minimum down to -2.0° Celsius by 2050 UTC.
Gale 0100 - 0130, 0525 - 0630, 0735 - increasing severe gale F9 at times late morning/early afternoon. Gale ceased soon after 1400 UTC, followed by a quick moderation and veer to 210°.