Snow and ice all part of Wick's weather for February 2021
Weather Watch by Keith Banks
Crystalline forms of water ice – snow, sleet and hail – are products of the atmosphere, while in frozen soils it manifests as black ice and ground frost. Finally, there is the ice that forms by the process of "inverse convection", over puddles and, of course, over much larger bodies of open water.
In the case of sea water, its density increases with falling temperatures, until freezing occurs. Sea water freezes at a lower temperature than fresh water, usually between minus 1.5C and minus 2.0C (29.3F to 28.4F), depending upon its salinity.
Icing of the soil often occurs after a snowfall, or hail. Land surfaces, in the shadows of mountains, or for example, forest roads that are not exposed to the energy supplied by the sun, are particularly vulnerable to frosts and icing.
Cold winds, particularly air streams with a high vapour content, also have a propensity to cause icing. If the moisture content (or humidity) of the air is high and exists in a supercooled state, freezing phenomena called rime and hoar frost can occur.
Unlike many other substances, when the temperature falls, the density of water does not continuously increase. Fresh water is actually at its most dense at a temperature of 3.98C (39.16F). This reduction in its density explains why ice floats, (the so called "water anomaly") and also why water freezes from above.
A review of Wick's historic record for mean air temperature for February revealed that February 2021 was the coldest since that of 2018. However, it is currently the 51st mildest in a series commencing from 1910.
In terms of precipitation, February 2021 was the least wet since that of 2015, and is presently the 14th driest in a series stretching back to 1910.
Winter 2020/21 was Wick's coldest since that of 2017/18. Mean air temperature was 3.76C (38.77F). The town's mean air temperature for winter, in terms of the averaging period 1981-2010 is 3.82C (38.88F).
Winter 2020/21 was Wick's wettest since that of 2016/17. The precipitation total was 172.0mm (6.77 inches). The long-term average quantity, for winter, is currently 211.2mm (8.31 inches).
Wick's mean air temperature for February 2021 was 3.90C (39.02F). The long-term average for February, in terms of the averaging period 1981-2010, is 3.75C (38.75F).
Wick's average maximum daytime air temperature for February 2021 was 6.23C (43.21F). The current long-term average for February is 6.40C (43.52F). A seasonally mild 10.0C (50.0F) was reached or exceeded on six dates. Highest maximum was 12.9C (55.2F), recorded on February 27. Lowest maximum was 0.4C (32.7F), observed on February 9.
Wick's average overnight minimum air temperature for February 2021 was 1.57C (34.83F). The long-term average for February is currently 1.10C (33.98F). Highest overnight air minimum was 7.2C (45.0F), witnessed on February 24.
There were eight air frosts. The lowest ambient temperature was a severe minus 8.1C (17.4F), logged on February 11.
The temperature fell to 0.0C (32.0F) or lower at 5cm over the grass on 13 dates. The lowest value recorded over the grass was minus 10.7C (12.7F), on February 9 and 11.
Precipitation was measurable on 19 dates. The total for the month was 30.2mm (1.89 inches), or 47.4 per cent of the long-term average for February. Th wettest day was February 17. The amount for the 24 hours commencing 9am (GMT) was 7.4mm (0.29 of an inch). Snow was visible over the grass at dawn on 11 dates. On February 9, the depth was 4.0cm (1.6 inches).
Wind velocities reached or exceeded gale force 8 (39.0mph/33.9knots) on 11 dates. The strongest wind velocity observed was during the half hour ending 9.30am (GMT), on February 13, when a force 7 south-easterly wind gusted up to 54.0mph/47.0knots, severe gale force 9 on the Beaufort scale.
