A red sky and aeroplane contrails seen over Canberra this morning were a sign that stormy weather is on the way. Daybreak in the nation's capital was nothing short of breathtaking today. Wispy cirrus clouds were illuminated in a mix of autumnal colours and three well-defined contrails could be seen streaking away from the rising sun. While the scene was indeed serene, it's also a warning that more ominous weather is on the way. High clouds and contrails form when there is enough moisture in the air about 10 to 12 kilometres above the ground. The latter phenomenon occurs when the water vapour and small particles released by an aeroplane's engines produce a line of small ice crystals in the sky. High cloud and contrails in Australia's subtropics can be a sign that a rain-bearing system is approaching from the west. This is certainly the case today. A low pressure system and associated trough are producing rain and storms over South Australia and western Victoria today, where towering cumulus clouds are injecting moisture high into the atmosphere. Strong upper-level winds are carrying this moisture eastward, causing high cloud over the ACT. The low and trough will move slowly towards the east in coming days produce a significant rain event across all of Australia's eastern states and territories between Thursday to Saturday. Canberra and the ACT should remain dry today, before wet weather develops on Friday. The city may receive close to 20mm from this event, which would be the heaviest rain in a couple of months. Dry conditions will return by Sunday as the system moves further east into the Tasman Sea. The pattern of high cloud preceding a rain event in the mid-latitudes underlies the old adage "red sky in the morning, shepherd take warning." Put simply, a red sky produced by high cloud at sunrise indicates that there is probably a rain-bearing weather system approaching from the west.