Weather for skydiving. Part 1.
Weather - the state of the atmosphere at a particular place and time as regards heat, cloudiness, dryness, sunshine, wind, rain, etc.
Weather is driven by temperature, air pressure and moisture differences, be it on micro or macro levels, and then nature’s endless search to create an equilibrium – which pretty much never works but causes oh so much fun along the way. It is an incredible performance of chaos, the main roles filled by dependable familiars, but the cast is replete with supporting roles and extras who may apparently initially signify nothing, but in the fullness of time, their effects may fill the sky with sound and fury.
Skydiving is a weather dependent activity.
Most people sort of guess that intuitively, but there are always a few who ask, yelling over 50 knot winds as the hail smashes their car and children, why we can’t jump today. We are pretty good with what we can jump in, but the things that ruin it quickly are low loud and winds getting over 45km/h. Sometimes it is a little less obvious - the upper winds might be very, very strong, but we might only be feeling light winds on the ground or it might seem like a nice hot summer’s day, but the air is really turbulent and unpredictable.
Skydiving is essentially a risk management activity and one of the risks or aspects we need to manage is weather. So! Beloved reader! Feast thine hungry eyes upon this mighty tome of learning! May thee live 10,000 years and be able to pick all cloud types at 10,000 yards!
It all began – the great Cloud-spiracy, in 1802 with Luke Howard and his seminal essay On The Modification of Clouds. No less exciting than a Tom Clancy novel and no more exciting than hitting yourself with a spoon, Howard decried that there were only three different cloud types rolling in the sky, just beyond the then reach of man. He looked and he saw: cirrus – fibres, cumulus – heaped and stratus – sheet. His motivation was to turn the years of esoteric individual knowledge spun and developed by practical forecasters – fishermen, farmers etc – into a science, befitting even the finest of Victorian amateurs.
With the advent of modern clouds living busy 24/7 lifestyles who are unable to be so neatly pigeonholed, the names have had to compound to reflect the variations and combinations available to even the least tech savvy of us 21st centuryers. The chart below illustrates really very neatly the different types of cloud currently available.
Source: BOM.
Why clouds? Why all these different types? Why now? Are they all connected? Does 5G cause them? Do they travel by zeppelin? You have questions. Of course you have questions. You’re a smart, independent thinking saviour of humanity and the constant need to question befits oh such a wise countenance.
Here, again from the BOM, are descriptions of the cloud types currently afflicting humanity.
The ten main types of cloud
The layer cloud types are known as stratiform and are classified as:
stratus—found in the low levels of the atmosphere, tend to produce a light drizzle;
altostratus—('alto' meaning high), found in the middle level, tend to be very good rain producing system for large areas across Australia, particularly inland;
nimbostratus—formed when altostratus undergoes further vertical development, allowing the cloud to hold more moisture, and causing the cloud base to lower and produce heavier rainfall; also appears darker in colour; and
cirrostratus—found in the higher levels of the atmosphere, white and wispy, and made of ice crystals. We often get a lot of halo activity with cirrostratus cloud, with the ice crystals refracting light around the moon and the sun.
The clumpy cloud, when in the lower part of the atmosphere, is classified as cumulus cloud:
cumulus—low level cloud which tends to produce short duration, fairly intense rainfall that is often very localised, meaning that rain falling at your house might not be falling at your neighbour’s a kilometre up the road;
stratocumulus—found in the lower levels, a blend between stratiform and cumuliform cloud and taking on appearances from both these cloud types, may produce drizzle;
altocumulus—found in the middle levels, looks like sheep in the sky, may produce light showers;
cirrocumulus—small, rippled, higher level cloud, does not produce precipitation; and
cumulonimbus—the largest cloud of all, forms in the lower layer of the atmosphere but extends through all three layers right to the top of the atmosphere. Also known as thunderstorm cloud, producing thunder and lightning.
Some of the more visually spectacular cloud happens very high up in the atmosphere, and is classified as cirrus cloud:
cirrus—formed of ice crystals moving very quickly through the atmosphere, occurring at temperatures around –40°C to –60°C, does not produce precipitation.
In Weather Part 2, we’ll talk about some of the different units and types of measuring or quantifying weather.