El Calafate is located in Patagonia, the southern part of the South American continent, at 50º20´26.7´´ South. Anf for that location, cold weather can be expected sometimes. But, what exactly?
Appropriate footwear is important. Be prepared to walk and for that, you need comfortable shoes to walk the paths with some stairs. You need a warm coat. Remember you will be in front of a huge mass of ice. You can find some wind from the Andes chain, so a warm coat is necessary, with a polar below... you know, the onion style, with different layers is perfect. Furthremore, trekking pants are perfect, but also rain pants are a good idea. If you`re thinking in mini trekking, to walk over the ice of the glacier, bring gloves, trekking (or better rain pants), sunglasses, and sunscreen, because the sun is reflected in the ice.
Enjoy your trip to El Calafate!