September Weather in Stanford, United States

Last updated: February 24, 2025

In September, Stanford, United States, experiences a mix of warmth and mild conditions typical of early autumn. Daily maximum temperatures can reach a scorching 39°C (103°F), while the average temperature rests comfortably at 18°C (66°F). Nighttime brings relief, with minimum temperatures dipping to a cool 10°C (50°F). Despite the high daytime heat, the month is characterized by minimal rainfall, with a mere 2 mm (0.1 in) of precipitation recorded over zero rainy days. Humidity levels hover around 55%, contributing to the overall pleasant and dry climate, making September an ideal time for outdoor activities in this picturesque region.

September Temperature in Stanford

September in Stanford, United States, marks a transition into the warmest stretch of the year, with temperatures showcasing a striking increase. The month begins with a minimum temperature of 10°C (50°F), and the average heightens to 18°C (66°F). However, the standout feature of September's climate is the impressive maximum temperature, soaring to 39°C (103°F), a sharp contrast to the cooler early months of the year. This pattern illustrates a gradual warm-up from the temperate summer months, reflecting a significant peak that hints at the lingering summer heat. As the month progresses, residents and visitors alike can savor the warm days while anticipating the milder conditions of autumn.

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

The chart illustrates September temperature patterns in Stanford, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends.
JanFebMarAprMayJunJulAugSepOctNovDec525354565863636565625652
Data source: Temperature data for Stanford 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 Stanford

In September, Stanford experiences a significant drop in precipitation, recording just 2 mm (0.1 in), with no measurable rainfall days. This minimal amount marks the continuation of a dry streak that begins in July and persists through August, where the region sees a complete absence of rain. This trend of low precipitation is characteristic of the late summer months, leading into the drier part of the year. As autumn approaches, October brings a slight uptick in rain, hinting at the seasonal shifts ahead. Thus, September serves as a transitional month, where the effects of the dry summer are palpable, yet it foreshadows the return of moisture in the coming weeks.

September Precipitation Trends in Stanford

The chart displays monthly precipitation patterns in Stanford, 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.
JanFebMarAprMayJunJulAugSepOctNovDec1051008633242012244788
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Stanford

In September, Stanford experiences a transition in its humidity levels, with a relatively low average of 55%. This marks a slight increase from the summer months, where August recorded the driest conditions at 54%. The trend reveals a steady decline in humidity from the beginning of the year, starting at a high of 82% in January, and reaching its lowest point in the mid-summer. As autumn approaches, September's modest humidity signals a shift towards the wetter conditions characteristic of the fall season, laying the groundwork for the more humid months ahead, such as October and November, which see increases to 62% and 78%, respectively. This cyclical pattern highlights Stanford's dynamic climate, oscillating between dry summers and wetter autumns.

September Average Humidity in Stanford

This chart illustrates the average monthly humidity levels in Stanford, 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.
JanFebMarAprMayJunJulAugSepOctNovDec82%84%82%78%71%64%59%54%55%62%78%80%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Stanford

As September rolls into Stanford, the UV Index remains notably high at 9, categorizing it as very high and necessitating careful sun exposure management. This month marks a slight decrease from August's peak levels, yet it still demands awareness as the optimal burn time is just 15 minutes. Following the extreme highs of summer, where June and July reached indices of 11, September signals a gradual tapering of aggressive sun intensity as the seasons shift. However, it still calls for protective measures to avoid skin damage, reminding residents to stay vigilant. For more detailed information about UV conditions, check out Stanford UV Index.

Maximum UV Index Levels in Stanford for September

The chart shows the monthly maximum UV Index (UVI) for Stanford 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.
JanFebMarAprMayJunJulAugSepOctNovDec3589101111109743
Data source: Stanford 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 Stanford

In Stanford, September marks a delightful transition as summer cedes to autumn, boasting an impressive 299 hours of sunshine. This month follows the high point of summer, where June reached its peak at 355 hours, and maintains a warm glow even as temperatures begin to cool. While the days are slightly shorter than in the height of summer, September still outshines the earlier months of the year, like January with a mere 151 hours and February's 216 hours. Interestingly, the overall trend shows a steady increase in sunshine from the bleak winter months, culminating in a vibrant summer before tapering off into the crispness of fall. As daylight lingers in September, it sets a beautiful tone for the coming months while reminding us of summer’s radiant legacy.

Monthly Sunshine Duration in Stanford: September Highlighted

The September sunshine duration represents the total number of hours Stanford 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.
JanFebMarAprMayJunJulAugSepOctNovDec151h216h263h296h341h355h349h320h299h276h225h194h
Data source: Stanford September Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in Stanford During September

September in Stanford, United States, brings a 58% chance of sunny weather, making it one of the more favorable months for sunlight as summer transitions into autumn. While February and May boast even higher percentages of sun at 55% and 62% respectively, September holds its own in the context of the annual weather trends. This month shows a slight decline from the sunniness of August (61%), yet it still surpasses the earlier months of the year, where chances of sunshine linger below the fifty percent mark. As the warm summer days give way to cooler evenings, September stands out as a delightful time to enjoy the outdoors under mostly sunny skies.

Percentage of Sunny Days in September in Stanford

The chart illustrates the percentage of sunny days in Stanford 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 Stanford experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec39%55%58%45%62%57%48%61%58%53%46%35%
Data source: Stanford September chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in Stanford in September

As summer wanes and September unfolds in Stanford, United States, daylight begins to gradually retreat, allowing for 12 hours of sunlight. This marks a gentle descent from the peak of 14 hours experienced during the summer months of June, July, and August. As the days grow shorter, the transition into autumn becomes evident, with daylight diminishing by an hour from the previous month. Interestingly, while July and August bask in maximum brightness, September serves as a bridge, linking the long, sun-drenched days of summer to the cooler, dimmer moments of fall, with October beckoning just around the corner, promising even shorter days ahead.

Average Daylight Hours in Stanford for September

The chart illustrates the variation in daylight duration in Stanford throughout the year, with September highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec9h 54m10h 49m11h 59m13h 11m14h 11m14h 41m14h 25m13h 31m12h 22m11h 10m10h 8m9h 36m
Data source: Stanford daylight hours, calculated by summing the hours between sunrise and sunset for each day.

September Winds in Stanford

As September arrives in Stanford, the gentle whispers of the wind begin to soften, with average gusts dropping to 2.0 m/s (4 mph), the lowest of the year. This decline follows a gradual increase from the earlier months, peaking at a breezy 3.0 m/s (7 mph) in May, signaling a transition from the lively summer air. August’s calmness sets the stage for September's tranquility, contrasting with the mild vigor experienced earlier in the season. Notably, this month marks a shift towards more serene conditions, as the cooling temperatures and changing leaves blend harmoniously with the subdued breezes, reflecting the gentle approach of autumn.

Average September Wind Speed in Stanford

The chart displays monthly wind speed patterns in Stanford, 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.
JanFebMarAprMayJunJulAugSepOctNovDec2.22.52.62.63.02.72.32.12.0 m/s2.41.82.4
Data source: Stanford September wind data, generated using information from the Copernicus Climate Change Service.

How September Weather in Stanford Compares to Other Months

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

In September, the weather offers a warm farewell to summer, with temperatures ranging from a mild 10°C (50°F) to a scorching 39°C (103°F), while enjoying a relatively dry spell with only 2 mm of precipitation. In stark contrast, January brings cooler temperatures, typically between 2°C (36°F) and 24°C (75°F), along with significant rainfall amounting to 105 mm (4.1 in) over roughly 7 days, making it one of the wettest months of the year. Additionally, December's humidity is lower at 55%, while January experiences a higher humidity level of 82%, contributing to a damp chill in the air. For more insights into the January climate, visit Stanford weather in January.

September and February present contrasting weather experiences. In September, temperatures can soar as high as 39°C (103°F), with an average of 18°C (66°F) and minimal precipitation, leading to a dry atmosphere with humidity around 55%. In stark contrast, February experiences much cooler temperatures, with a maximum of only 24°C (76°F) and average highs near 11°C (53°F). This month is considerably wetter, receiving about 100 mm (3.9 in) of rainfall across approximately 8 days, and the humidity rises significantly to 84%. For more details on February weather, you can check Stanford weather in February.

September typically showcases a warm climate, with temperatures ranging from a cool 10°C (50°F) at night to a scorching peak of 39°C (103°F) during the day. The month boasts minimal precipitation, averaging only 2 mm (0.1 in) and experiencing no rainy days, making it a relatively dry time. In contrast, March presents a much cooler atmosphere, with temperatures fluctuating between a minimum of 4°C (40°F) and a maximum of 25°C (78°F). This month is marked by significantly higher precipitation, averaging 86 mm (3.4 in) over 11 days, and notable humidity levels of 82%. For more detailed weather insights specific to March, you can visit Stanford weather in March.

Comparing the weather conditions in September and April reveals significant differences. September typically enjoys warmer temperatures, with a minimum of 10°C (50°F) and an average high reaching up to 39°C (103°F), while April sees cooler weather with a minimum of 6°C (42°F) and a maximum of 30°C (87°F). Additionally, September is characterized by very low precipitation, averaging only 2 mm (0.1 in) with no rainy days, in stark contrast to April, which experiences more moisture with 33 mm (1.3 in) of rainfall spread over five days. The humidity levels also reflect these differences, as September has a moderate humidity of 55%, while April is much more humid at 78%. For a deeper understanding of April weather specifics, you can refer to Stanford weather in April.

September and May present contrasting weather profiles. September typically boasts warmer temperatures with a minimum of 10°C (50°F) and an average of 18°C (66°F), peaking at a sweltering 39°C (103°F). In contrast, May has cooler conditions, with minimum temperatures around 8°C (46°F) and an average of 15°C (59°F), reaching a maximum of 29°C (84°F). Additionally, September enjoys very low precipitation, registering only 2 mm (0.1 in) across 0 days, while May experiences significantly more rainfall at 24 mm (0.9 in) over 2 days. Humidity levels also differ, with September at 55% compared to May's higher humidity of 71%. For more details on the weather in May, refer to Stanford weather in May.

In September, the weather tends to be warmer compared to June, with average temperatures reaching 18°C (66°F) and maximums soaring up to 39°C (103°F). In contrast, June has a slightly lower average temperature of 17°C (63°F) and a maximum of 35°C (96°F). Both months experience similar low precipitation levels of 2 mm (0.1 in) with no rainy days; however, September's humidity at 55% is lower than June's 64%. This difference in humidity may contribute to a more comfortable feel in September compared to the more humid June days. For more detailed information, you can check Stanford weather in June.

When comparing the weather in September and July, we can see some notable differences. September features a wider temperature range, with minimums dropping to 10°C (50°F) and maximums soaring up to 39°C (103°F), compared to July's more moderate range of 11°C (53°F) to a high of 29°C (84°F). Both months experience very little precipitation, with September receiving just 2 mm (0.1 in) and July being completely dry at 0 mm (0.0 in). Humidity levels are slightly lower in September at 55%, compared to 58% in July, making September feel a bit more comfortable despite the higher maximum temperatures. For a more detailed look at July weather, check out Stanford weather in July.

September's weather offers a slight decrease in minimum temperatures, averaging 10°C (50°F), compared to August's 12°C (54°F). However, both months share the same average temperature of 18°C (65°F), with September experiencing a notable increase in maximum temperatures, reaching up to 39°C (103°F), while August peaks at a more moderate 35°C (96°F). Both months recorded very little precipitation, with September seeing only 2 mm (0.1 in) of rain, matching August's dry spell of 0 mm (0.0 in). Humidity levels remain fairly stable, with September at 55% and August slightly lower at 54%. For more detailed insights, you can check Stanford weather in August.

In September, temperatures range from a minimum of 10°C (50°F) to a maximum of 39°C (103°F), presenting some sweltering days with an average of 18°C (66°F). The month is relatively dry, receiving only 2 mm of precipitation over no rainy days and experiencing a humidity level of 55%. In contrast, October sees a slight decrease in temperatures, with a minimum of 7°C (45°F) and a maximum of 33°C (92°F), averaging 17°C (63°F). This month is characterized by increased rainfall, totaling 24 mm over just one day, and a rise in humidity to 62%. Overall, October brings cooler temperatures and more moisture compared to September. For more details, visit Stanford weather in October.

September and November present contrasting weather conditions. In September, temperatures range from a minimum of 10°C (50°F) to a scorching maximum of 39°C (103°F), with an average of 18°C (66°F). The month enjoys very little precipitation, recording only 2 mm (0.1 in) over no rainy days, and the humidity is relatively moderate at 55%. In stark contrast, November experiences cooler weather, with temperatures ranging between a minimum of 4°C (39°F) and a maximum of 27°C (80°F), averaging 13°C (56°F). This month sees significantly more precipitation, totaling 47 mm (1.9 in) over five rainy days, and the humidity rises to 78%, increasing the dampness in the air. For more details on conditions, you can check Stanford weather in November.

In September, the weather is generally warm, with temperatures ranging from a minimum of 10°C (50°F) to a scorching maximum of 39°C (103°F) and an average of 18°C (66°F). The humidity levels are relatively moderate at 55%, and there is little to no rainfall, with only 2 mm recorded over the month. In contrast, December brings cooler and wetter conditions, with temperatures dropping to a minimum of 3°C (37°F) and averaging 11°C (52°F), peaking at 22°C (72°F). Precipitation significantly increases in December, totaling 88 mm (3.5 in) over 9 wet days, and humidity rises to 80%, creating a marked shift in the climate. For more detailed insights, check out Stanford weather in December.

Compare Stanford's Climate with Cities Worldwide

Conclusion: What to Expect From September Weather in Stanford

As September unfolds in Stanford, the weather transitions into a warm and inviting period, markedly different from the cooler months that precede it. With average temperatures settling around a pleasant 18°C (66°F) and peaks soaring to a toasty 39°C (103°F), this month offers a taste of late summer bliss. The low precipitation—notably, no rain in sight—coupled with a moderate humidity level of 55%, creates ideal conditions for outdoor activities and gatherings. This dry spell not only amplifies the allure of the golden Californian sun but also sets the stage for a refreshing shift as the season gradually turns. For more insights on Stanford's climate throughout the year, explore Stanford Climate.