The floodwaters of 1952 began with the weather of 1951. That year, extensive spring flooding, a damp summer, and early winter rainfall left the ground of the Upper Midwest unusually wet. When the temperature finally dropped below freezing, the ground frost which formed was unusually deep, becoming a barrier through which the spring meltwater of 1952 could not pass. The resulting runoff into area rivers was thus much larger than usual, causing many of the Mississippi's tributaries to flood by early April, inundating communities and farmland upriver from the Twin Cities. As these waters critically swelled the Mississippi, heavy rains and increased runoff from a weekend heat wave finally sent the river into flood stage in St. Paul on April 9th.