Shepparton has a warm-temperate inland climate — hot dry summers and cool winters with occasional frosts. The city is not on the coast and sits in a flat valley, which means it can get genuinely hot in January and February (over 40°C is not unusual) and cold but rarely freezing in July.
Spring (September–November) is the most appealing time to visit. The orchards blossom, temperatures are pleasant, and the valley looks its best. Autumn (March–May) is harvest season, when the fruit-processing industry is at full swing and roadside stalls sell fresh produce at low prices.
Summer visits are possible if you're heat-tolerant and come prepared — the air-conditioned Shepparton Art Museum is a reasonable refuge. Winter is fine for a short visit but most of the outdoor appeal is reduced.