September weather forecast and climate
St. Louis, MO

A beautiful twilight view of the Gateway Arch in St. Louis, Missouri, with a distant view of the city buildings mirrored in the waterfront
A beautiful twilight view of the Gateway Arch in St. Louis, Missouri, with a distant view of the city buildings mirrored in the waterfront
September, the first month of the autumn, in St. Louis, is still a warm month, with average temperature fluctuating between 80.2°F (26.8°C) and 60.6°F (15.9°C).

Temperature

In September, the average high-temperature in St. Louis marginally drops, from a hot 88°F (31.1°C) in August, to a warm 80.2°F (26.8°C). In September, in St. Louis, the average low-temperature is 60.6°F (15.9°C).

Humidity

The average relative humidity in St. Louis is 71.6%.

Rainfall

In St. Louis, in September, during 7.4 rainfall days, 3.13" (79.5mm) of precipitation is typically 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

May through October are months without snowfall in St. Louis.

Daylight

The average length of the day in St. Louis is 12.4h.

Sunshine

In September, the average sunshine in St. Louis is 7.9h.

UV index

In St. Louis, the average daily maximum UV index is 7. A UV Index of 6 to 7 symbolizes a high health vulnerability from unprotected exposure to the Sun's UV rays for average individuals.
Note: The daily maximum UV index of 7 in September interpret into the following advice:
Take precautions and utilize sun safety practices. Protection against the skin and eye damage is required. 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.

What is the temperature in September in St. Louis?

In September, the average high-temperature is 80.2°F (26.8°C), and the average low-temperature is 60.6°F (15.9°C).

What is the average humidity in September in St. Louis?

In September, the average relative humidity in St. Louis, Missouri, is 71.6%.

How much does it rain in St. Louis in September?

In St. Louis, during September, the rain falls for 7.4 days and regularly aggregates up to 3.13" (79.5mm) of precipitation.

When it does not snow in St. Louis?

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

What is the average length of the day in September in St. Louis?

The average length of the day in September in St. Louis is 12.4h.

How many hours of sunshine does St. Louis have in September?

In September, the average sunshine in St. Louis is 7.9h.

What is the UV index intensity in September in St. Louis?

In St. Louis, Missouri, the average daily maximum UV index in September is 7. A UV Index of 6 to 7 symbolizes a high hazard to health from unsafe exposure to the Sun's UV rays.
Average temperature in September - St. Louis, MO
  • Average high temperature in September: 26.8°C

The warmest month (with the highest average high temperature) is July (31.7°C).
The month with the lowest average high temperature is January (4.4°C).

  • Average low temperature in September: 15.9°C

The month with the highest average low temperature is July (21.7°C).
The coldest month (with the lowest average low temperature) is January (-4.6°C).

Average humidity in September - St. Louis, MO
  • Average humidity in September: 71.6%

The month with the highest relative humidity is December (75.8%).
The month with the lowest relative humidity is April (63.5%).

Average rainfall in September - St. Louis, MO
  • Average rainfall in September: 79.5mm

The wettest month (with the highest rainfall) is May (119.9mm).
The driest month (with the least rainfall) is February (56.9mm).

Average rainfall days in September - St. Louis, MO
  • Average rainfall days in September: 7.4 days

The month with the highest number of rainy days is May (11.9 days).
The month with the least rainy days is September (7.4 days).

Average snowfall in September - St. Louis, MO
  • Average snowfall in September: 0mm

The month with the highest snowfall is January (142.2mm).
Months with the least snowfall are May, June, July, August, September and October (0mm).

Average snowfall days in September - St. Louis, MO
  • Average snowfall days in September: 0 days

The month with the highest number of snowfall days is January (4.7 days).
Months with the least snowfall days are May, June, July, August, September and October (0 days).

Average daylight in September / Average sunshine in September - St. Louis, MO
  • Average daylight in September: 12.4h

The month with the longest days is June (Average daylight: 14.8h).
The month with the shortest days is December (Average daylight: 9.5h).

  • Average sunshine in September: 7.9h

The month with the most sunshine is July (Average sunshine: 10h).
The month with the least sunshine is December (Average sunshine: 4.2h).

Average UV index in September - St. Louis, MO
  • Average UV index in September: 7

Months with the highest UV index are June, July and August (UV index 9).
Months with the lowest UV index are January and December (UV index 2).