Compared to locations in the east, the area warms rather gradually early in the year, with the last measurable snow typically occurring in late April and precipitation totals beginning to increase; May snow occurs several times per decade. Toward the middle of the year, storms typically develop over the Black Hills during the afternoon and move onto the plains in the evening. Only in April through June have calendar-day precipitation amounts exceeding been observed. June 15, 1963, with , holds the single-day rainfall record; the record-wettest month is May 1996 with . Rapid City has an average of twenty clear to partly cloudy days and 67 percent of its possible sunshine in June. This is the traditional "flood" season for Rapid and other creeks in the Eastern Hills. Temperatures warm rapidly as summer approaches.