THIN AND INDISTINCT clouds overlaid the blue, letting a warm diffused light through. Shade and sun alike were pleasant. A green mist of new leaves rose along the abrupt slope of Morningside Avenue. A BMW SUV showed off its sound system through open windows, then accelerated away in a hurry. People tottered toward the park under the weight of loaded coolers and folding furniture. The scrim of cloud steadily by imperceptible stages thickened to gray. Mylar numeral balloons swayed and leaned over 18th and 3rd birthday picnics. A fetid smell drifted over from the water.