The short answer is: sometimes. An urban planter box can stay outside all winter without cracking only if it is frost-resistant, well drained, and suitable for your climate. Cracking is usually caused by water trapped in the soil or in the container material expanding as it freezes and thaws. Urban conditions make this more important because balconies and rooftops can be windier and more exposed than a garden.
Check the material first. Fiberglass, high-quality UV-stable plastic, frost-rated composite, and properly constructed metal or wood containers are generally lower risk, though metal can rust and wood can rot. Thin ceramic, glazed terracotta, and decorative concrete are more likely to crack, especially if they already have chips or hairline cracks.
Drainage is critical. Make sure drainage holes are open, add feet to lift the box off the surface, and use a free-draining potting mix rather than dense garden soil. Before the first hard freeze, stop watering, remove saucers, and tip out standing water. Do not let snow or ice block the drainage holes.
Plants and soil also matter. Frozen soil expands, and a container packed solid with saturated soil puts more pressure on the sides. If the planter is not frost-proof, empty it and store it in a shed or move it to a sheltered spot. For a frost-proof box, you can leave it planted, but mulch the top and avoid disturbing frozen soil. In very cold or exposed urban sites, wrap the outside with insulation or group planters together for wind protection.
No container is completely crack-proof. If you want the lowest risk, choose a winter-rated planter, keep it draining freely, and inspect it before and after winter. If the box is fragile or has already cracked, do not leave it outside full of wet soil.