Precipitation Associated with a Cold Front , December 7 - 9 / 1956

During the period December 7-9, 1956, a slow-moving cold front over the Central States brought prolonged precipitation to an area extending from' northern Texas northeastward into New England (fig. 1). Amounts of over 3 inches accumulated in portions of southern Illinois and Indiana. Accumulations of 1 inch or more were reported from northeastern Oklahoma to Lake Erie,. Prior to this period, a cold front had moved through the Northern Plains St'ates at about 15 miles per hour until 0630 GMT, December 6. It then became nearly stationary from Oklahoma to Illinois, although the portion north of Illinois continued an eastward movement'. By 0630 GMT, December 7, the front extended along a line from southern Oklahoma through the eastern Great Lakes to a Low center in the St. Lawrence River Valley (fig. 2). A High pressure system moved southward behind the front and covered most of the Northern Plains States by 0630 GMT, December 7. The upper air flow at, 0300 GMT, December 7 (fig. 3), was marked by a broad belt of southwesterly winds at' 500-mb. over all the United States except the Pacific Coast States. A trough lay from northern Idaho south-southwestward through central California and a large-amplitude ridge west of it extended northward into the Gulf of Alaska. The flow aloft east of the trough was remarkably free of curvature, and remained almost straight west-southwesterly over the Central States during the entire period of rainfall. Several very minor waves formed along the front, but none developed significantly. The surface.High over the Northern Plains States had continued to intensify and, moving southward, had merged with an even stronger High pressure cell, also moving southward, which had formed in British Columbia. By 0630 GMT, December 9 (fig. 4) there was a 1055-mb. High near Salt Lake City, Utah, with a strong ridge extending southeastward. During the 72 hours from 0630 GMT, December 6 to 0630 GMT, December 9, the portion of the front from Texas to the Great La.kes area moved only about 200 miles southeastward. One section, from western Tennes-see to West Virginia, was almost stationary during the last 24 hours of that period. The southwestern section, however, maintained a slow southeastward drift until 1830 GMT, December 8, when it lay along a line from Nashville, Tenn. to Shreveport, La. and Del Rio, Tex. During the next 12 hours the portion of t,he front sout'h-west of Nashville accelerated. By …