WEATHER WATCH: Getting to grips with ‘soft hail’
Snow pellets, (also known as graupel or soft hail), are distinctive, essentially spherical, opaque grains of ice that are created when small supercooled water droplets collide and freeze instantly upon impact.
They can also form when ice crystals strike supercooled water droplets when both exist within a cloud.
When this happens, air becomes trapped between them creating their diagnostic non transparent appearance.
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However, small hail, another form of solid precipitation is formed by a different process and are distinguishable from soft hail because small hail pellets are translucent, permitting the passage of light through them.
This form of solid precipitation forms when ice particles or snow cores fall into a layer of the atmosphere where the water droplets that are present, are not in a supercooled state, and the freezing process has been slowed down by the release of a greater amount of latent heat possessed by the water droplets.
Latent heat is the 'hidden energy' that is either liberated or absorbed by a substance such as water when it changes state without changing it's actual temperature as the process takes place.
In this case the formation of small hail. It is called the latent heat of crystallization or freezing.
The conditions, together with the mechanisms that are necessary to create graupel and small hail occur within Cumulus congestus and Cumulonimbus clouds, where convective processes cause powerful updraughts that propel water droplets upwards.
Frozen particles created at the tops of these convective clouds grow during their descent and fall into another updraught and are carried upwards again.
This process may be repeated until the pellets become too heavy for the updraughts to toss upwards again, and gravity and cold downdraughts cause the graupel and small hail to fall out of the clouds.
Graupel and small hail are not the same as hailstones.
Unlike hailstones,that are frequently large irregular shaped solid lumps of ice, graupel and small hail are small and spherical with fragile structures that tend to crumble and disintegrate when minimal pressure is applied.
Graupel pellets with diameters of more than 5mm (0.2 inches) are very unusual.
However, hailstones, the products of very vigorous convection that occurs in the most violent Cumulonimbus clouds, with diameters in the range 25mm-50mm (1 inch to 2 inches) not uncommon, particularly during the spring and summer months.
A review of Wick's archive for mean air temperature for June 2024 showed that it was the coolest since that of 2016.
However, a closer look at the values for a series of Junes stretching back to 1910, confirmed that it is currently the 29th warmest.
In terms of precipitation,June 2024 was the least wet since that of 2022.
However, analysis of the town's historic record for rainfall for June commencing 1910 revealed that it is presently the 50th equal wettest in the series.
The precipitation total was identical in June 1974.
Wick's mean air temperature for June 2024 was 11.48C (52.66F).
The long term value in terms of the averaging period 1991-2020 is 11.25C (52.35F).
Wick's average daytime maximum air temperature for June 2024 was 14.65C (58.37F).
The current long term average for this parameter is 14.28C (57.70F).
Highest maximum air temperature was 22.8C (73.0F), recorded on June 24.
However, a maximum of 19.9C (67.8F), noted on June 2 was also noteworthy for the time of the year.
Lowest maximum was 10.1C (50.2F), observed on June 11.
Wick's average overnight minimum air temperature for the month was 8.30C (46.94F).
The long term average in terms of the current 30 year averaging period is 8.21C (46.78F).
Highest minimum air temperature was 12.3C (54.1F), witnessed on June 24.
The lowest minimum was 4.2C (39.6F), recorded on June 6 and 9 respectively.
Lowest temperature at 5cm over the grass was 2.3C (36.1F), recorded on June 13.
Precipitation was logged on 25 dates, the total amount recorded for the month was 56.2mm (2.21 inches), or 101, six per cent of the present long term average quantity for June.
Wettest day of the month was June 13. The total amount recorded for the 24 hours commencing 9am (GMT) was 9 4mm (0.37 of an inch).
Wind velocities reached or exceeded gale force 8, (39mph/33.9knots on four dates.
The windiest day was June 28 when a force 6 west-north-west wind gusted up to 51.8mph/45.0knots, severe gale force 9 on the Beaufort scale.
