August weather forecast and climate
St. Louis, MO

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

Temperature

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

Heat index

The average heat index in August is evaluated at a torrid 100.2°F (37.9°C). Take special precautions - heat exhaustion and heat cramps are expected. Heatstroke may occur with lengthy activity.
Take into consideration that the heat index values are calculated for shade and light wind conditions. Exposure to direct sunshine can increase heat index values by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'feels like', 'felt air temperature', 'real feel', or 'apparent temperature', is calculated by taking the relative humidity value for a specific location and factoring it into the air temperature reading. This effect is subjective, depending on the activity and individual's heat perception influenced by various reasons (metabolic differences, wind, clothing). 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 cools itself through perspiration, as excessive warmth is removed from the body through sweat evaporation. High relative humidity reduces the evaporation rate, resulting in a lower heat removal rate from the body, causing the perception of being overheated. If the body can not disperse the excessive heat and body temperature reaches conditions of hyperthermia, above 99.5°F (37.5°C) to 100.9°F (38.3°C), thermal conditions are potentially life-threatening.

Humidity

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

Rainfall

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

Snowfall

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

Daylight

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

Sunshine

In August, the average sunshine in St. Louis is 8.7h.

UV index

Months with the highest UV index in St. Louis are June through August, with an average maximum UV index of 9. A UV Index reading of 8 to 10 represents a very high health risk from the exposure to the Sun's UV rays for the average person.
Note: The average daily UV index of 9 transform into the following instructions:
Take extra precautions. Protection against sun damage is required. Seek shade and minimize exposure to direct Sun in a period between 10 a.m. and 4 p.m. when UV radiation is most intense; keep in mind that shade structures like parasols or canopies do not provide perfect sun protection. 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.