Although nowhere in Australia could really be described as 'cold' in April (especially by travelers used to North American or European cold weather!), temperatures do drop by mid-autumn.
The only main towns with average highs above 90° F (30° C+) in April are Darwin and Townsville, in far northern parts of the country. Even Alice Springs, in the heart of the Northern Territory outback, sits more comfortably around 82° F (28° C). In southern cities like Sydney, Melbourne, Adelaide, and Hobart, average highs are in the low 70s F (low 20s C). These temperatures, of course, are average daytime highs, and in many places you should expect overnight temperatures to be much lower, even (especially) in the desert. You'll definitely need a sweater when traveling in Australia in April.
Sydney sees most of its rain in autumn and early winter, so travelers to Sydney in April should expect rain. But, temperatures aren't very cold (with an average high of 73° F/ 23° C), so come prepared with an umbrella and light jacket and the rain shouldn't be a problem.
In contrast to Sydney, other southern cities like Melbourne, Adelaide, and Hobart generally remain dry in April (and year-round), and Brisbane has less rain than in the summer months. The rainy season in the tropical north also eases off in April, and Darwin is drier than it has been for months.
Crowds and Costs
April to September is generally considered the high season for travel to Australia, as the temperatures are cooler. But, in reality different parts of the country experience highs throughout the year. So, although April can be considered the beginning of the high season, this doesn't necessarily mean it will be more or less busy than at other times, depending on where you want to go. There's a lot of geographic variation.
Easter often falls in April, and when it does, expect for there to be more Australians at the most popular tourist spots, especially theme parks (such as on the Gold Coast). Schools and students have a break around Easter, so many families travel or get out and about, even if just within their home area. Flights may be more expensive at this time and book up quicker, so book as far enough in advance as possible.
Where to Go
In many ways, April is an ideal time to plan a big trip around Australia because so many places are not just accessible but comfortable at this time of year. You can enjoy cooler temperatures in the southern cities that are ideal for walking around and sightseeing, and then travel up to Queensland or the Northern Territory for some warmth, and even some beach time (in northern New South Wales and southern Queensland).
If beach time is a priority for you, be aware that deadly box jellyfish linger in northern areas (northern Western Australia and northern Queensland) through April and even into May. You won't be able to swim in the sea, as these jellyfish can kill an adult in minutes. Stick to further south in Queensland (such as Brisbane and the Gold Coast), the area around Perth in Western Australia, or northern New South Wales. Even in mid-autumn the temperatures should be warm enough to swim comfortably.
What to Do
Aside from swim in the sea in the north, there are very few limits on what you can do in Australia in April! Check out the museums and galleries in the major cities (especially Sydney, Melbourne, and Canberra), go hiking in Tasmania or the Blue Mountains west of Sydney, learn about ancient Indigenous Australian culture in Alice Springs and Uluru, lounge on a beach on the east coast, tour the wineries of the Barossa Valley in South Australia... as long as you're prepared for some lingering heat in the north, and some autumnal weather further south, you can do a lot in April.
April is a good time to embark on a road trip, such as between Melbourne and Sydney, Sydney and Brisbane, Brisbane and Cairns, or even Adelaide to Uluru. Conditions in the desert in April are still pretty hot in the daytime, but if you have an air-conditioned vehicle and take emergency supplies, this is a better time for a road trip than the summer.
ANZAC Day, on 25th April, is a major holiday in Australia (and New Zealand) that commemorates those killed in war. Travelers interested in history, especially military history, might want to be in Canberra on ANZAC Day, when a dawn service is held at the Australian War Memorial.
Sydney Royal Easter Show. This fun, family-friendly event that runs for two weeks around Easter. It's been running for almost 200 years (the first show was in 1823), and is Australia's largest annual event. Although it started life as an agriculture show, you can expect fairground rides, music, dance, and other entertainment.
Barossa Valley Vintage Wine Festival. This wine festival is held every two years, just outside Adelaide. Food and wine enthusiasts won't want to miss this event in one of Australia's premier wine-producing regions.
Other events are held throughout the country around Easter, so look out for these if Easter falls in April.
Traveling to Australia in April? Check out these great itineraries
Outback Adventure: Uluru and Alice Springs - 5 Days. Begin at Uluru and discover the ancient Red Centre and its surroundings. Then, travel to Alice Springs to tour the cultural highlights of the desert city.
Southeast Australia Self-Drive - 22 Days. Explore southeast Australia on this combination self-drive and flying tour, and see many of the region's highlights on this comprehensive 22-day itinerary.