I've written this up for my personal bushwalking blog - any and all critiques, corrections and comments most welcome!
Red sky at night, sailor’s delight. Red sky at morning, sailor take warning.
Thus goes the old saying, and there’s a lot of truth in it. The sky can tell us a great deal about what the weather is going to get up to. Reading the weather is a skill that few of us possess these days, but one that walkers should try to acquire. After all, when you’re on the third day of a six-day trek, the only place you’re going to get a weather report is from the sky above you.
Of course, you should always try to get the most up-to-date forecasts possible before you leave, so you have some idea what to expect. However, with Tasmania's weather, expect the unexpected. Snow in midsummer is not unknown, on the Central Plateau. Weather can change drastically, in a very short time. Knowing a bit about what warning signs to look for can be very helpful, at the least.
Wind and most especially clouds are your most reliable indicators of the weather that you can expect in the coming hours and days.
Wind direction is very important, but its meaning is also very dependent on your locality. It is important to bear in mind that the information about wind direction here is strictly relevant to Tasmania.
South-Westerly winds mean colder, wetter air in Tasmania. Just how wet and how cold depends on the time of year, and exactly where in Tasmania you are.
Easterly and North-Easterly to South-Easterly winds are good news for North-West to South-West Tasmania, producing clear skies and mild days for the Western half of the island. For Eastern Tasmania, though, such winds bring cool and cloudy, and possibly wet weather to the East.
Persistent light Westerlies or windless conditions indicate a stable atmosphere, and no severe weather. Warm sunny days with smaller, puffy cumulus clouds or “mackerel skies” are likely to stay that way, and also into the next day. Clouds that break up or reduce near sunset herald a fine day to follow. Morning dew or frost is also a good sign, as is morning fog that burns off rapidly.
Clouds are a great indicator of approaching fronts and wind changes. If you can see two sets of clouds in the sky, one low and moving with the present wind direction, while the other is much higher and moving in a different direction, the upper set indicates the direction the change is coming from.
Wispy, cirrus “mare’s tails” high in the sky form in the direction the wind is blowing in the upper sky.
Rippled clouds also show wind direction, but contrary to what you might expect, the ripples form at right angles to the wind.
Cirrus clouds often show an approaching front. When cirrus thickens enough to cover most of the sky, it is known as cirrostratus, and a change is likely in about 24 hours. Halos around the sun or moon are associated with cirrostratus. Cirrostratus mean that rain or snow are likely in coming days.
If cirrostratus thickens further into altostratus, extensive rain or snow are on their way.
Thickening and growing cumulus also means worsening weather. If you see the classic, anvil-shaped cumulonimbus thunderheads building, best to get to shelter soon!
Low, dark, ragged and patchy nimbostratus clouds mean heavy rain is probably between hours or at most half a day away.
Large white cloud banks with a furry, diffuse top, approaching from the South or West, indicate a very cold change involving snow. Get to cover or lower elevations.
So, what about the red sky at night?
Well, that depends on the exact colour red. A red sky at night means that the setting sun is sending its light through a high concentration of dust particles. A light, pinkish sky is generally a fairly good sign. This usually indicates high pressure and stable air coming in from the west. Basically good weather will follow. A deep fiery red, on the other hand, more likely indicates bad weather to come.
And a red sky at morning?
If the morning sky is red, it means high water content in the atmosphere. So, rain is on its way.
Sources:
Burroughs, Crowder, Robertson, Vallier-Talbot, Whitaker, 2008, Weather, The Five Mile Press
Leaman, D. E., 2001, Step into history in Tasmanian reserves, Leaman Geophysics
McManners, H, 1995, The Backpacker’s Handbook, HarperCollins