In a typical year (if there is such a thing), the temperature gradually rises as the days lengthen in spring and gradually falls as daylight wanes in the autumn. Average temperature charts reflect this pattern but, as we all know, nature is not focused on human records.
During many of our transition seasons, periods of excessive cold may disrupt expected trends. While these episodes are merely inconvenient and frustrating for impatient humans, they can be deadly for some species of wildlife. Early insectivore migrants, such as eastern phoebes and tree swallows, travel north in response the the lengthening daylight, only to find that their natural food has been suppressed by a prolonged, unseasonable freeze. In like manner, a late period of cold weather may destroy a variety of natural flowers, impacting both the creatures that feast on their nectar and those that rely on their fruit. Heavy spring or early autumn snows are notorious for culling newborn and aging mammals, thinning herds and offering sustenance to scavengers.
In concert with natural predation, such weather events serve to keep populations in check and, in the big picture, are essential to healthy ecosystems. Of course, we humans, anxious to reconnect with the joys of spring, are not inclined to appreciate these unseasonable setbacks.