September Weather in Decorah, United States

Last updated: February 24, 2025

In September, Decorah, United States, experiences a dynamic weather profile characterized by a maximum temperature of 32°C (90°F) and an average of 18°C (65°F), presenting a pleasant transition into autumn. Nighttime chills can drop the temperature as low as 2°C (35°F), creating a striking contrast. The month witnesses an aggregate precipitation amount of 123 mm (4.8 in) across 10 days, contributing to a relatively high humidity level of 74%. This blend of warm days and cool nights, coupled with the occasional rainfall, makes September a uniquely refreshing month in Decorah.

September Temperature in Decorah

As September arrives in Decorah, the transition to cooler weather becomes evident. With nighttime lows averaging 2°C (35°F), the crisp air heralds the onset of autumn. Daytime temperatures typically reach a comfortable 18°C (65°F), making it an ideal time for outdoor activities amidst the vibrant changing leaves. This month can still boast warm days, peaking at around 32°C (90°F), reflecting a lingering summer warmth, before the chill of October sets in. Overall, September offers a delightful balance of cool nights and pleasantly warm afternoons, inviting both relaxation and exploration in this picturesque corner of the United States.

September Weather in Decorah: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Decorah, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends.
JanFebMarAprMayJunJulAugSepOctNovDec192035455971747064493527
Data source: Temperature data for Decorah generated using information from the Copernicus Climate Change Service.
Choose your preferred temperature unit
The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Decorah

In September, Decorah experiences a noticeable increase in precipitation, receiving 123 mm (4.8 in) over 10 days. This marks a continuation of the wetter trend that begins in May, when rainfall peaks at 155 mm (6.1 in), and it reflects the region's transition to autumn. Notably, September’s precipitation is higher than the preceding months of July and August, suggesting a shift towards more substantial rainfall as the summer warmth fades. This pattern sets the stage for October, which also boasts significant precipitation at 133 mm (5.2 in). Overall, the month showcases the dynamic weather typical of the changing seasons in the upper Midwest.

September Precipitation Trends in Decorah

The chart displays monthly precipitation patterns in Decorah, with values for each month alongside September's data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September's conditions compare to those of other months.
JanFebMarAprMayJunJulAugSepOctNovDec395264801551301061101231335338
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Decorah

In September, Decorah experiences a notable shift in humidity, averaging 74%, which marks a decrease from the higher levels seen in the summer months. This drop reflects a transition toward autumn, as humidity falls from a peak of 75% in both July and May. Interestingly, despite the approach of cooler weather, September still maintains a comfortable level of humidity, higher than the dryer late summer of August at 69%. This gradual decline indicates the onset of the more variable weather patterns typical of fall, as the area prepares for the more humid conditions of November at 88%.

September Average Humidity in Decorah

This chart illustrates the average monthly humidity levels in Decorah, with September's data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, allowing you to see how September's humidity levels compare to other months.
JanFebMarAprMayJunJulAugSepOctNovDec84%85%84%83%75%79%75%69%74%79%88%82%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Decorah

As September rolls into Decorah, residents can expect a high UV Index of 8, signaling a continued need for sun protection as summer's warmth lingers. This very high exposure category means that burn time is notably short at just 15 minutes, echoing the peak conditions experienced in the preceding summer months. Although the UV Index dips slightly from August's peak, it remains crucial to remain cautious when enjoying outdoor activities, especially as you transition into the cooler autumn months. Checking the Decorah UV Index regularly can help you prepare for safe sun exposure as the seasonal changes unfold.

Maximum UV Index Levels in Decorah for September

The chart shows the monthly maximum UV Index (UVI) for Decorah in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues.
JanFebMarAprMayJunJulAugSepOctNovDec34589101098532
Data source: Decorah September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

September Sunshine in Decorah

As summer fades, September in Decorah continues to bask in a generous 261 hours of sunshine, marking a graceful transition from the sun-drenched days of July and August. This month’s sunlight, while slightly diminished from the peak summer months, still outshines the earlier part of the year, significantly above January's dreary 129 hours. The consistent upward trend from the depths of winter illuminates the vibrant shift of seasons; with each month, the increase in sunlight culminates in the refreshing brilliance of late summer and early fall. As golden leaves adorn the landscape, September's softer sunlight provides a perfect backdrop for enjoying the last warm days before the cooler fall sets in.

Monthly Sunshine Duration in Decorah: September Highlighted

The September sunshine duration represents the total number of hours Decorah experiences direct sunlight during the month of September, excluding cloudy or obstructed periods. This chart compares the sunshine duration of September with the other months of the year.
JanFebMarAprMayJunJulAugSepOctNovDec129h194h231h232h257h332h359h324h261h200h191h180h
Data source: Decorah September Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in Decorah During September

As summer fades into autumn, September in Decorah brings an exciting transition in weather, boasting a 63% chance of sunny days. This marks a significant increase from the earlier months, with sunny probabilities rising steadily from a mere 25% in January to this high in September. It's a time when the lingering warmth of summer still graces the region, surpassing the rainy tendencies of spring and early summer. Interestingly, after reaching its peak in September, the likelihood of sunshine begins to dip again in October, illustrating the ephemeral nature of pleasant weather as the days grow shorter. This makes September a golden opportunity for those seeking to bask in the sun before autumn fully takes hold.

Percentage of Sunny Days in September in Decorah

The chart illustrates the percentage of sunny days in Decorah throughout the year, with September highlighted. It highlights the variation in sunshine across each month and provides an overview of the typical frequency of sunny days, offering insights into how often Decorah experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec25%33%42%32%35%55%51%57%63%42%41%36%
Data source: Decorah September chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in Decorah in September

As September unfolds in Decorah, the days begin to shorten, offering approximately 12 hours of daylight. This gradual decline from the summer peak of 15 hours in June reflects the overarching seasonal shift, where the vibrant energy of August's 13 hours gives way to the crispness of autumn. The transition is a reminder of nature's rhythm, as daylight hours wane into October, which welcomes just 10 hours of sunshine. This trend highlights the inevitable approach of winter, shaping the landscape and lifestyle of Decorah's residents as they adjust to the cooler days ahead.

Average Daylight Hours in Decorah for September

The chart illustrates the variation in daylight duration in Decorah throughout the year, with September highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec9h 23m10h 31m11h 57m13h 26m14h 41m15h 18m14h 58m13h 51m12h 26m10h 58m9h 41m9h 1m
Data source: Decorah daylight hours, calculated by summing the hours between sunrise and sunset for each day.

September Winds in Decorah

As September rolls into Decorah, the wind picks up slightly, averaging 3.5 m/s (8 mph), setting the stage for the change of seasons. This increase in wind speed aligns with a gradual upward trend observed as summer transitions into autumn, a shift that typically brings more brisk breezes. Following the warmer months, where winds notably dipped to their calmest in July and August, this slight uptick heralds the approach of fall. Notably, September's winds lay the groundwork for the more vigorous gusts that emerge in November, showcasing nature's rhythm as it prepares for the colder months ahead.

Average September Wind Speed in Decorah

The chart displays monthly wind speed patterns in Decorah, with values for each month shown alongside September's data, which is highlighted for easy comparison. It illustrates the average wind speed, offering insights into how September's wind conditions compare to the rest of the year.
JanFebMarAprMayJunJulAugSepOctNovDec3.43.64.24.13.93.42.93.03.5 m/s3.74.54.2
Data source: Decorah September wind data, generated using information from the Copernicus Climate Change Service.

How September Weather in Decorah Compares to Other Months

The weather in Decorah 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 Decorah and find detailed weather information for every month.

September and January present strikingly contrasting weather conditions. In September, temperatures range from a mild 2°C (35°F) at night to a warm average of 18°C (65°F) and can reach as high as 32°C (90°F) during the day. This month also experiences considerable rainfall, with about 123 mm (4.8 in) spread over 10 days and a humidity level of 74%. In contrast, January is characterized by frigid temperatures, with lows plunging to -33°C (-28°F) and an average temperature of -7°C (20°F), peaking at only 11°C (51°F). The precipitation is significantly lower in January at 39 mm (1.5 in) over 7 days, accompanied by a higher humidity of 84%. For a closer look at what to expect in January, visit Decorah weather in January.

September and February present stark contrasts in weather conditions. In September, temperatures range from a chilly minimum of 2°C (35°F) to a warm maximum of 32°C (90°F), with an average of 18°C (65°F). This month sees considerable rainfall, accumulating to 123 mm (4.8 in) over approximately 10 days, accompanied by a humidity level of 74%. In contrast, February features much colder temperatures, with a minimum plunging to -34°C (-28°F) and an average of -7°C (20°F), while the maximum can reach a milder 18°C (65°F). February experiences much lower precipitation of 52 mm (2.0 in) over about 8 days, but the humidity is higher at 85%. For a closer look at February's climate specifics, check out Decorah weather in February.

In September, temperatures range from a chilly minimum of 2°C (35°F) to a warm maximum of 32°C (90°F), with an average of 18°C (65°F), while March features colder weather, with temperatures dipping as low as -25°C (-12°F) and peaking at 21°C (69°F), averaging around 2°C (35°F). The month of September experiences a higher precipitation level of 123 mm (4.8 in) over approximately 10 days, compared to March's 64 mm (2.5 in) over 8 days. Additionally, March has a slightly higher humidity level at 84%, compared to September's 74%. For more details about March weather, you can visit Decorah weather in March.

When comparing the weather in September and April, there's a noticeable contrast in temperature and humidity. September boasts a warmer range with minimums around 2°C (35°F) and averaging 18°C (65°F), peaking at a maximum of 32°C (90°F). In contrast, April starts much cooler, with temperatures dipping to a minimum of -11°C (13°F) and averaging only 7°C (45°F), although it can still reach a comfortable 26°C (80°F). Precipitation levels also differ slightly, with September receiving 123 mm (4.8 in) over 10 days, compared to April's 80 mm (3.2 in) over the same number of days. Additionally, April's humidity is slightly higher at 83%, compared to September's 74%. For a more detailed look at April's weather, visit Decorah weather in April.

In comparing the weather of September and May, September typically presents warmer temperatures, with averages around 18°C (65°F) and maximums reaching up to 32°C (90°F). In contrast, May features slightly cooler average temperatures at 15°C (59°F) but can also experience high maximums, peaking at 33°C (92°F). Precipitation is more pronounced in May, with 155 mm (6.1 in) over 15 days, compared to September's 123 mm (4.8 in) over 10 days. Humidity levels remain quite similar, hovering around 74% in September and 75% in May. For a closer look at May's weather, you can visit Decorah weather in May.

In comparing the weather of September and June, we can observe notable differences in temperature and humidity levels. September generally starts with cooler temperatures, with a minimum of 2°C (35°F) and an average of 18°C (65°F), peaking at 32°C (90°F). In contrast, June has a milder temperature range, with lows around 8°C (48°F), an average of 22°C (71°F), and highs reaching 35°C (95°F). Both months experience significant precipitation, but September sees 123 mm (4.8 in) over about 10 days, while June slightly exceeds that with 130 mm (5.1 in) over 11 days. Additionally, humidity in September averages around 74%, while June is slightly higher at 79%. For more detailed insights, check out Decorah weather in June.

When comparing the weather in September and July, notable differences can be observed. September experiences a wider temperature range, with minimums as low as 2°C (35°F) and maximums reaching 32°C (90°F), leading to an average temperature of 18°C (65°F). In contrast, July tends to be warmer overall, with minimums of 11°C (53°F) and maximums of up to 34°C (93°F), averaging 23°C (74°F). Precipitation levels are fairly similar; September sees 123 mm (4.8 in) over 10 days, while July has slightly less at 106 mm (4.2 in), also over 10 days. Humidity levels are comparable, with September at 74% and July at 75%. For a more detailed look at July weather, you can visit Decorah weather in July.

In comparing the weather patterns of September and August, we see notable differences in temperature and humidity. September experiences cooler minimum temperatures, dropping to 2°C (35°F), while August's minima are significantly higher at 10°C (51°F). Though the average temperatures are similar, with September averaging 18°C (65°F) and August slightly warmer at 21°C (70°F), September also sees a higher maximum temperature of 32°C (90°F) compared to August's high of 34°C (94°F). Additionally, September has slightly more precipitation at 123 mm (4.8 in) over 10 days, while August totals 109 mm (4.3 in) over the same number of days. Humidity is also higher in September at 74% compared to August’s 69%. For a more detailed look at August weather, visit Decorah weather in August.

September and October present a notable shift in weather patterns. In September, temperatures typically range from a mild 2°C (35°F) at night to a warm 32°C (90°F) during the day, with an average of 18°C (65°F). The month sees a moderate level of precipitation at 123 mm (4.8 in) across about 10 days, and humidity sits at 74%.

In contrast, October experiences a more pronounced shift toward cooler conditions, featuring a minimum temperature of -7°C (20°F) and a lower average of 10°C (50°F), though it can still reach a maximum of 30°C (86°F). Precipitation slightly increases to 133 mm (5.2 in) over 11 days, accompanied by a higher humidity level of 79%. For more detailed information on October weather, check out Decorah weather in October.

September and November present stark contrasts in weather patterns. September typically enjoys mild temperatures with a minimum of 2°C (35°F) and an average of 18°C (65°F), peaking at 32°C (90°F). This month also sees considerable precipitation, averaging 123 mm (4.8 in) over about 10 days, coupled with a humidity level of 74%. In contrast, November experiences much colder temperatures, with a minimum plunging to -16°C (3°F) and an average of just 2°C (35°F), while the maximum reaches only 22°C (72°F). Precipitation decreases to 53 mm (2.1 in) over 7 days, and humidity rises to 88%. For more details on November weather, you can visit Decorah weather in November.

September and December present strikingly contrasting weather patterns. September features a temperature range from a mild 2°C (35°F) to a warm 32°C (90°F), with an average of 18°C (65°F), and it typically experiences 123 mm (4.8 in) of precipitation over about 10 days. The humidity in September hovers around 74%, contributing to a warm, often muggy atmosphere.

In contrast, December brings much colder temperatures, with a minimum of -23°C (-9°F) and an average of -3°C (28°F). The maximum temperature can reach 20°C (68°F), but overall it is significantly chillier than September. December records much less precipitation—38 mm (1.5 in) over just 6 days—and sees higher humidity at 82%, which can create a colder, more biting sensation in the air. For a detailed look at December weather specifics, check Decorah weather in December.

Compare Decorah's Climate with Cities Worldwide

Conclusion: What to Expect From September Weather in Decorah

As September unfolds in Decorah, the weather presents a notable transition compared to the summer's warmth, making it a time of change and refreshment. Daily temperatures begin to dip from the highs of previous months, averaging a comfortable 18°C while the maximum can still reach a warm 32°C on clearer days. With 75% humidity and 123 mm of rainfall over about 10 days, this month marks a shift towards a more autumnal feel, characterized by cooler mornings and the unmistakable scents of the season. For those keen on understanding how these conditions play into the broader climate patterns, more insights can be found at Decorah Climate.