Last updated: February 24, 2025
September in St. Louis, United States, showcases a dynamic weather profile that is both inviting and refreshing. With maximum temperatures peaking at a warm 35°C (95°F), the city basks in sunny days, while averages linger around a comfortable 22°C (73°F). On the cooler end, nighttime lows can drop to 7°C (45°F), offering a crisp contrast. Rainfall sees 56 mm (2.2 in) spread over 7 days, contributing to the 76% humidity, creating a rich, lush atmosphere perfect for fall activities. Whether you're enjoying warm afternoons or cool evenings, September presents a delightful blend of warmth and refreshing breezes in St. Louis.
In September, St. Louis experiences a delightful transition as summer yields to autumn. The temperatures reflect this shift, with minimums around 7°C (45°F), rising to a comforting average of 22°C (73°F), and peaking at a warm 35°C (95°F). This month often showcases a perfect blend of sunny days and cooler evenings, inviting residents to relish outdoor activities. The gradual decline from the summer's peak temperatures heralds the onset of crisper air, making it an ideal time for enjoying the city's parks and vibrant festivities. As the warmth lingers, the changing leaves gradually add a picturesque touch to the skyline, marking a beautiful transition in the heart of the Midwest.
In September, St. Louis experiences a noticeable decline in precipitation, with only 56 mm (2.2 in) of rain over just 7 days—the lowest monthly total of the year. This marks a shift from the more tumultuous summer months, particularly August, which sees significantly higher rainfall at 130 mm (5.1 in) over 11 days. As the summer heat begins to wane, September's drier conditions suggest a transitional period, paving the way for the wetter spells of fall. The pattern of decreasing rainfall and precipitation days in September highlights a seasonal shift, offering a respite before the arrival of autumn storms.
September in St. Louis marks a notable shift in humidity levels, as the average drops to 76%, a refreshing change from the summer months. This decrease follows a trend observed since June, where humidity peaked at 83%. As the city gradually transitions from the sweltering heat of summer, September's lower humidity levels contribute to more comfortable conditions, making it an ideal time for outdoor activities. Interestingly, this marks the beginning of a trend toward cooler, drier air, setting the stage for the crispness of fall, with humidity remaining stable at 76% into October before rising again in the colder months. Overall, September offers a brief but welcome respite from the higher humidity that characterizes the preceding summer months.
As summer transitions into the cooler days of fall, September in St. Louis maintains a very high UV Index of 9, indicating that sun exposure remains a significant consideration. With a burn time of just 15 minutes, it's crucial for residents and visitors alike to be mindful of sun protection as they enjoy outdoor activities. Although the UV Index dips slightly from the peak levels of the summer months, it remains essential to stay vigilant against overexposure. Adopting protective measures now can help prevent skin damage and ensure that your fall adventures are not interrupted. For more information on UV levels and safety tips, check out the St. Louis UV Index.
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As summer gives way to autumn, September in St. Louis enjoys a delightful transition with approximately 290 hours of sunshine, marking a gradual decline from the peak of 348 hours in July. This month showcases a notable change, smoothly following August's abundant light yet still shining bright enough to keep the warmth of summer lingering. Overall, the sunny days are a reminder of the vibrant energy that fills the city, contrasting with the diminishing hours seen as the year moves toward winter. With September's sunshine, residents and visitors alike can bask in a perfect blend of warmth and cool breezes, heralding the beautiful fall season ahead.
As September rolls into St. Louis, the weather begins to shift, revealing an inviting 64% chance of sunny days—one of the highest probabilities for sunshine throughout the year. This trend marks a significant increase compared to the summer months, where sunshine chances hover around the mid to high 40s. The gradual transition from the sweltering heat of August, which offers a 47% chance of sun, sets the stage for a beautiful early autumn. Observing the progression from spring through summer, it's clear that September provides a delightful opportunity for outdoor activities under clear, blue skies, making it a favored month for locals and visitors alike.
As summer fades into autumn in St. Louis, September presents a gentle transition in daylight duration. With an average of 12 hours of daylight, the month marks a slight decrease from the longer summer days, wherein June, July, and August bask in 14 hours of sun. This gradual dimming heralds the approach of fall, following a peak in daylight that inspires outdoor activities and bright evenings. Notably, as the year progresses towards winter, daylight hours will continue to diminish, cascading down to just 9 hours in December. This rhythmic ebb and flow not only enhances the charm of each season but also invites residents to savor the lingering warmth of September before the chill of autumn fully sets in.
As September rolls into St. Louis, the gentle breeze brings a slight uptick in average wind speed to 3.0 m/s (7 mph), marking a subtle shift from the languid summer months. This increase hints at the transition towards autumn, where winds begin to pick up after the quiet calm of July and August, which both lingered at around 2.1 to 2.4 m/s (5 mph). These late summer lulls give way to a more dynamic atmosphere, as the air starts to cool, positioning September as a bridge to the brisker October winds, which see a return to higher speeds at 3.5 m/s (8 mph). This pattern of fluctuating winds invites a refreshing change, signaling not just a change in season, but also an invigorating shift in St. Louis's climate tapestry.
The weather in St. Louis changes throughout the year, offering a unique experience in each season. Below is a month-by-month comparison of September's weather with other months, highlighting differences in temperature, precipitation, and other key factors. Click on each section to discover seasonal trends in St. Louis and find detailed weather information for every month.
In September, the weather is warm and inviting, with average temperatures around 22°C (73°F) and a maximum reaching up to 35°C (95°F), making it ideal for outdoor activities. However, the month sees some precipitation, averaging 56 mm (2.2 in) over about 7 days, along with a comfortable humidity level of 76%. In stark contrast, January brings a chilling cold, with average temperatures plummeting to around 0°C (32°F) and dipping as low as -22°C (-7°F). Although it receives slightly more precipitation at 76 mm (3.0 in) over 8 days, the colder conditions and higher humidity of 82% create a frosty atmosphere. For a more detailed look at January weather, check out St. Louis weather in January.
In September, temperatures range from a mild 7°C (45°F) at night to a warm 35°C (95°F) during the day, with an average of 22°C (73°F). The month experiences around 56 mm (2.2 in) of precipitation over approximately 7 days, paired with a humidity level of 76%. In contrast, February brings a dramatic chill, with temperatures plunging to a minimum of -19°C (-1°F) and an average of just 2°C (35°F), though it can occasionally reach a pleasant maximum of 24°C (76°F). This month sees slightly higher precipitation at 80 mm (3.2 in) over about 10 days, with humidity reaching 80%. For more details on February weather specifics, visit St. Louis weather in February.
September and March present distinctly different weather patterns. In September, temperatures range from a pleasant 7°C (45°F) at night to a warm 35°C (95°F) during the day, with an average of 22°C (73°F). The month sees a moderate level of precipitation, totaling 56 mm (2.2 in) over 7 days, and humidity levels hover around 76%. In contrast, March experiences much cooler temperatures, with lows dipping to -17°C (2°F) and daytime highs reaching 27°C (81°F), averaging just 8°C (47°F). This month is notably wetter, with 131 mm (5.2 in) of rainfall recorded over 12 days, and humidity at a slightly higher 80%. For more specific insights into the conditions in March, you can visit St. Louis weather in March.
September and April showcase contrasting weather patterns. In September, temperatures range from a milder 7°C (45°F) at night to a warm 35°C (95°F) during the day, with an average of 22°C (73°F). The month experiences moderate precipitation of 56 mm (2.2 in) over about 7 days, accompanied by a humidity level of 76%. In contrast, April sees a broader temperature swing, featuring chilly nights at -4°C (24°F) and warmer days peaking at 30°C (87°F), with an average of 13°C (55°F). This spring month is wetter, with precipitation totaling 129 mm (5.1 in) over approximately 11 days and slightly higher humidity at 80%. For an in-depth look at April's weather, you can visit St. Louis weather in April.
When comparing the weather in September and May, September typically offers warmer averages with temperatures ranging from a minimum of 7°C (45°F) to a maximum of 35°C (95°F), while May's temperatures are slightly cooler, with a minimum of 4°C (40°F) and a maximum of 34°C (94°F). Precipitation is notably higher in May, accumulating around 145 mm (5.7 in) over about 14 days, compared to September's 56 mm (2.2 in) across 7 days. Humidity levels are also higher in May, reaching 82%, in contrast to September’s 76%. For more detailed insights, you can check out St. Louis weather in May.
In comparing the weather between September and June, notable differences emerge. September experiences a broader temperature range, with minimums at 7°C (45°F) and maximums reaching 35°C (95°F), averaging around 22°C (73°F). The month sees less precipitation, totaling 56 mm (2.2 in) over about 7 days, accompanied by a humidity level of 76%. In contrast, June is warmer overall, with minimum temperatures at 12°C (54°F) and a higher average of 25°C (77°F), peaking at 36°C (98°F). However, June is significantly wetter, receiving 101 mm (4.0 in) of rainfall over 11 days and maintaining higher humidity at 83%. For more detailed insights, you can check out St. Louis weather in June.
When comparing the weather in September to that in July, it is clear that September tends to be cooler and slightly drier. In September, the minimum temperature drops to 7°C (45°F) while the average temperature is 22°C (73°F), reaching a maximum of 35°C (95°F). In contrast, July experiences milder lows at 16°C (61°F) with an average of 26°C (80°F) and peaks at a scorching 38°C (101°F). Furthermore, September sees about 56 mm (2.2 in) of precipitation over 7 days, whereas July is wetter with 97 mm (3.8 in) across 11 days, leading to a higher humidity level of 81% in July compared to September's 76%. For further insights, you can explore St. Louis weather in July.
In comparing the weather of September and August, September showcases a cooler temperature range with a minimum of 7°C (45°F) and an average of 22°C (73°F), compared to August's higher minimum of 12°C (54°F) and average of 25°C (76°F). Both months reach similar maximum temperatures, peaking at 35°C (95°F) in September and slightly higher at 36°C (96°F) in August. Precipitation is notably lower in September, with 56 mm (2.2 in) falling over 7 days, while August experiences significantly more rain, totaling 130 mm (5.1 in) across 11 days, indicating a wetter climate. Humidity levels are also slightly less in September at 76%, compared to August's 80%. For a more detailed look at August weather, check out St. Louis weather in August.
September and October exhibit contrasting weather patterns that reflect the transition from summer to fall. In September, temperatures range from a minimum of 7°C (45°F) to a maximum of 35°C (95°F), with an average of 22°C (73°F). The month sees about 56 mm (2.2 in) of precipitation over 7 days and maintains a humidity level of 76%. In contrast, October experiences cooler temperatures, with a minimum of -4°C (26°F), an average of 15°C (59°F), and a maximum of 34°C (93°F). Precipitation increases to 105 mm (4.1 in) over 11 days, while humidity remains steady at 76%. This shift in weather highlights the onset of autumn's chill and increased rainfall. For more details on October weather, you can visit St. Louis weather in October.
When comparing the weather in September and November, a stark contrast emerges. September typically boasts milder temperatures, with an average of 22°C (73°F) and a maximum of 35°C (95°F), along with a relatively low precipitation of 56 mm over 7 days. In contrast, November experiences much cooler conditions, where the average dips to just 7°C (44°F), with temperatures occasionally falling as low as -13°C (9°F). Additionally, November sees slightly higher precipitation at 75 mm over 9 days and increased humidity at 85%. For a more detailed look at November weather patterns, check out St. Louis weather in November.
September and December weather showcase significant contrasts. In September, temperatures range from a comfortable minimum of 7°C (45°F) to a warm maximum of 35°C (95°F), with an average of 22°C (73°F). This month experiences 56 mm (2.2 in) of precipitation over about 7 days, and the humidity sits at 76%. In contrast, December brings much colder temperatures, with lows touching -18°C (0°F) and an average of just 4°C (39°F), while the maximum only reaches 22°C (71°F). Precipitation levels remain similar, at 59 mm (2.3 in) across the same number of days, but the humidity increases to 86%. For more detailed insights about December's weather, visit St. Louis weather in December.
As September unfolds in St. Louis, it marks a notable transition from the sweltering heat of summer to more moderate conditions. While the temperatures can still reach a warm peak, the overall climate begins to cool down, offering a welcome respite with average highs that are more comfortable. The humidity remains a consistent factor, creating a somewhat sticky atmosphere, although rain events occur less frequently than in the summer months. This month typically features a mix of pleasant sunny days and occasional showers, resulting in a vibrant and lively environment. For a detailed look at how September fits within the broader context of St. Louis' weather patterns, visit St. Louis Climate.