August weather forecast and climate
St. Louis, MO

The last month of the summer, August, is another tropical month in St. Louis, with average temperature fluctuating between 69.4°F (20.8°C) and 88°F (31.1°C).

Temperature

In St. Louis, the average high-temperature is almost the same as in July - a still hot 88°F (31.1°C). The average low-temperature, in St. Louis, is 69.4°F (20.8°C).

Heat index

The average heat index is computed to be a very hot 100.2°F (37.9°C). Take special precautions - heat exhaustion and heat cramps are expected. Heatstroke may occur with lengthy activity.
Note that heat index values are valued for light wind and location in the shade. With exposure to direct sunlight, the heat index may be increased by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'real feel', 'apparent temperature', 'feels like', or 'felt air temperature', is an index that combines air temperature and relative humidity to determine the human-perceived temperature equivalent. Additional factors like activity, wind, metabolic differences, and clothing affect individual temperature impact. Bear in mind that direct sunshine exposure increases weather impact, and may raise heat index by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are especially crucial for babies and toddlers. Young children are generally more endangered than adults, as they usually less sweat. And also, due to larger skin surface relative to their small bodies and higher heat production as a result of their activity.
The human body normally cools itself by perspiration, as evaporated sweat carries heat away from the body. With a lot of moisture in the air, the evaporation process is not as effective, and the body does not cool down as efficiently, creating a perception of overheating. When heat gain exceeds the level the body can remove, body temperature begins to rise, and heat-related illnesses and disorders may develop.

Humidity

In August, the average relative humidity in St. Louis is 70%.

Rainfall

In August, in St. Louis, the rain falls for 8.2 days. Throughout August, 2.99" (75.9mm) of precipitation is accumulated. In St. Louis, during the entire year, the rain falls for 112.6 days and collects up to 40.96" (1040.3mm) of precipitation.

Snowfall

In St. Louis snow does not fall in May through October.

Daylight

In St. Louis, the average length of the day is 13.6h.

Sunshine

The average sunshine in August in St. Louis is 8.7h.

UV index

June through August, with an average maximum UV index of 9, are months with the highest UV index in St. Louis. A UV Index estimate of 8 to 10 represents a very high health hazard from the exposure to the Sun's UV rays for ordinary individuals.
Note: In August, the average maximum UV index of 9 translate into the following recommendations:
Take special precautions, as unprotected eyes and skin can be burned and damaged quickly. The Sun's UV radiation is most powerful between 10 a.m. and 4 p.m. To the extent possible, limit exposure to the direct sun during these hours. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes. A broad-spectrum sunscreen of SPF 30+ should be liberally applied and re-applied every two hours, and immediately after an outdoor workout or a swim.