Anybody that's been keeping a close eye on the alps recently will know two things: there hasn't been a big bout of natural snow so far this winter and the slopes are looking pretty good for mid-June. So, how are some of Australia's ski slopes still covered in snow despite a lack of strong cold fronts during the past fortnight? Part of the reason is due a fortunate sequence of early-winter weather systems. A strong front at the end of May brought up to 50cm of natural snow to parts of the alps, while a weaker front brought another 5-10cm last week. In between these snowfalls, high pressure systems centred predominantly to the west and north of the Alps have sustained freezing overnight temperatures, low relative humidity at times and most importantly, no heavy rainfall. In Australia, the only thing more important than getting new snow on the ground is not losing what's there. The first half of June has been pretty good for maintaining snow. In addition to this fortunate sequence of natural effects, there has also been help from technology. The string of freezing nights and cold days during the last fortnight has allowed artificial snowmaking to help maintain a base. Snow guns have ensured skiers and boarders have plenty of cover to slide around on. It's worth noting that artificial snow is still real snow. It's the environmental conditions necessary for snow formation that are being created artificially in this process. Snow guns work by releasing compressed air and water droplets of varying sizes at the same time into the sky over a ski slope. Natural processes take over as soon as this air/water mix level the gun. The compressed air rapidly expands, which causes a rapid drop in temperature. This starts to freeze the water droplets and the ambient (or natural outside) temperatures does the rest before the newly made snow touches the ground. Artificial snowmaking needs to be done when the conditions outside help snow form, instead of melt. While this seems obvious, it may come as a surprise that good quality snow can be artificially made even when the outside temperature is above freezing. The air just needs to be dry enough. This may seem odd, but think of a hot and muggy day. You feel the heat more on these days because the high relative humidity in the air is hindering the ability of sweat to evaporate from your skin (evaporation cools the air around it). It's the same with artificial snowmaking. If the relative humidity is low enough, it will help remove heat from water droplets in the air so efficiently that snow can be made in temperatures above zero degrees. Last night was an good example in the alps. A temperature inversion caused the top of Thredbo to be warmer than the lower slopes. At 11pm the air temperature was five degrees at Thredbo Top Station and minus two at Perisher Valley, which is about 200 metres lower. Despite the high temperature on top of Thredbo, the relative humidity at Thredbo was so low (17 per cent) that snow could be made. Because the high temperature was overcompensated by low humidity last night, snow guns were firing down the mountain and the result was a fresh cover on the ground this morning. A large high pressure system will be anchored over Australia's southeast until at least the middle of next week. While this means there won't be much natural snow falling, the snow guns will be firing.