After a long, brutal summer, enveloped in hot, dry air, we in Missouri are now bathed by the remnants of Hurricane Isaac. The familiar humidity of the American Midwest has returned, exceeded now by the swampy feel of the Tropics. Moisture collects on windows and drips from plants and, even between showers, a fine mist hangs in the air.
Now near the center of Isaac's broad circulation, the wind is calm and low clouds hang above Columbia, trapping thick, balmy air near the surface. Though the copious moisture is subtropical in origin, it has broken the intense heat that persisted through most of the summer. Humid air is less dense than its dry, desert counterpart and cannot achieve the high temperatures that baked Missouri for the past few months. In addition, the process of condensation consumes heat, falling rain cools the air and the blanket of dense cloud cover reflects the solar radiation.
Our current swampy air is thus cooler than the dry air mass that is poised to return in the coming days. As the storm's center drifts off to the east, its backside moisture will give us a final dose of welcome rain before the heat and sunshine return. Fortunately, now that we are two months beyond the summer solstice, our longer nights should keep the intense summer heat at bay and, over the next few weeks, we will slip toward the mild, colorful days of autumn.
