| description abstract | In the charting of clouds associated with the storm which developed on a cold front over Arkansas and moved northeastward it is found that the first clouds formed were Ci. These clouds were preceded by cooling at high levels, presumably by lifting of the upper strata. Later, as these clouds thickened into As, and their bases lowered, they reached Ac which had formed meanwhile. The falling ice crystals probably grew rapidly in the supercooled Ac thereby causing a rapid lowering of the Ns ceiling until snowfall commenced at the ground. As the storm continued to develop, the highest cirrus moved well ahead while the original Ac layer became extensive and the chief producer of precipitation. A lower layer formed at the cold front, which grew enough over the area of occlusion, to reach the middle layer. Other low clouds continued within the cold air mass throughout the storm period. All cirrus that could be detected, except the edge of the uppermost layer found at the rear of the storm near the end of the study, formed at temperatures above ?39C. Schaefer (1947) reports ?39C as the critical temperature above which nuclei must be present for cirrus formation. | |
