CLIMATE: Clark County is cold in winter and is quite hot with occasional cool spells in summer. Precipitation during the winter frequently occurs as snowstorms, and during the warms months is chiefly showers, often heavy, when warm moist air moves in from the south. Total annual rainfall is normally adequate for corn, soybeans and small grain.

In winter, the average temperature is 15 degrees F and the average daily minimum temperature is 5 degrees. In summer, the average temperature is 70 degrees and the average maximum temperature is 82 degrees.

The total annual precipitation is about 21 inches. Of this, about 16 inches, or almost 80 percent, usually falls in April through September. The growing season for most crops falls within this period. The average seasonal snowfall is 32 inches. On the average, 46 days of the year have at least 1 inch of snow on the ground.

The average relative humidity in mid-afternoon is about 60 percent. Humidity is higher at night, and the average dawn is about 80 percent. The sun shines 70 percent of the time possible in the summer and 55 percent in winter. The prevailing wind is from the south-southeast in the summer and from the northwest in winter. Average wind speed is highest, 14 miles per hour in spring.

Tornadoes and severe thunderstorms strike occasionally. These storms are local and of short duration and result in very severe damage in small, localized areas. Hailstorms occur during the warmer of the part of the year in irregular patterns and in relatively small areas.

Physiography, Relief, and Drainage: More than half of Clark County is on the Coteau des Prairies (Flint, 1955). This part of the county is gently rolling to undulating. Basins are numerous in this area, and external drainage is nearly nonexistent. The western edge of the Coteau des Prairies trends nearly north-south a few miles west of central Clark County.

The western one-third of the county is in the James Basin Physiographic area. Drainage in this area is generally westward to the James River. The area is characterized by small basins, some of which are barely perceptible. It is nearly level, except near drainageways. The drainageways are trenched near their headwaters along the western edge of the Coteau des Prairies.

Most streamflow occurs in the spring and after heavy rains.

Infrastructure: Vienna and Willow Lake are the only communities currently served by the railroad. South Dakota highways 20, 25, and 28 and US Highway 212 are the main highways. Most rural areas are served by a network of secondary roads that is adequate for travel. A small airport is located at Clark.

Natural Resources: Soil is the most important natural resource in Clark County. It provides a growing medium for crops and the grasses grazed by livestock. Other natural resources are water, sand and gravel and wildlife.

The principal source of water for domestic livestock is shallow wells. The water from shallow wells is in glacial till or outwash material. About 70 percent of the county is underlain by glacial aquifers. Depth to the aquifers ranges from 1 to 585 feet. The yields and the quality of water from the wells vary greatly. In general the glacial aquifers are suitable for human and livestock use. In some cases, however, treatment may be needed for domestic use because of excess iron or manganese and because of hardness. The sodium hazard is low, but high or very high salinity may require careful management if the water is used for irrigation, even if drainage is adequate. The bedrock aquifer that underlies the county yields soft water unsuitable for irrigation because of excess sodium.

Significant deposits of sand and gravel extend roughly from north to south through the center of the county. Gravel is also in the northeast and northwest corners of the county and, to a lesser extent, in a few other areas.

White-tailed deer and upland game birds, such as ring-necked pheasants, are the major wildlife resources in the county. The numerous potholes and wetlands provide good wildlife production areas. A small herd of antelope inhabits the Crocker Hills area. Coyote and fox are the main predators in the county. Bass, bluegill, crappies, and perch provide fishing opportunities in stock-water impoundments. Walleye, northern pike, and perch inhabit Round Lake and Bailey's Lake.