It has to be in the 70's for me, though I usually wear sandals a little later in the fall than I do early in the spring. The issue here is that although the temperature has reached 70 on a few days, the days still begin either in the 30's or low 40's. The mornings are COLD, so I cannot wear sandals out of the house first thing in the morning, even if they would be okay later in the afternoon.
Upon further consideration, maybe it is a "vibe". Because things are still so chilly here in the evenings and mornings, and the breeze can still be cold, it just doesn't feel like sandal weather, even if the temperature did reach the mid-70's by afternoon (which it hasn't yet). I agree that this is the season for loafers or flats or closed-toe shoes with no (showing) socks. The summer will likely be long and hot; no need to rush the open footwear.
