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September Weather in Sun Valley, United States

Last updated: June 24, 2025

In Sun Valley, United States, the average temperature in September hovers around 18°C (64°F), making it a pleasant time to visit. However, temperatures can range significantly, with a minimum of 0°C (32°F) and soaring to a maximum of 36°C (97°F). During this month, expect about 8 mm (0.3 in) of precipitation spread over 2 days, and enjoy an average humidity of 41%.

September Temperature in Sun Valley

In September in Sun Valley, the average temperature is 18°C (64°F). The maximum can reach 36°C (97°F) and the minimum can be as low as 0°C (32°F). Be prepared for a wide range of temperatures, and pack accordingly for your trip!

September Weather in Sun Valley: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Sun Valley, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Sun Valley, September typically has an average temperature of 18°C (64°F), with highs reaching up to 36°C (97°F) and lows dropping to around 0°C (32°F).
JanFebMarAprMayJunJulAugSepOctNovDec323338475566747364504132
Data source: Temperature data for Sun Valley generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Sun Valley

In Sun Valley in September, the precipitation amount is 8 mm (0.3 in) over the course of 2 days.

September Precipitation Trends in Sun Valley

The chart displays monthly precipitation patterns in Sun Valley, 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. In Sun Valley, September typically receives around 8 mm (0.3 inches) of precipitation spread over approximately 2 days.
JanFebMarAprMayJunJulAugSepOctNovDec9187713239811118333965
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Sun Valley

In Sun Valley in September humidity is 41%. With an average temperature of 18°C (64°F), this humidity feels like a mild and comfortable atmosphere for traveling, allowing you to explore without feeling overly sticky or fatigued.

September Average Humidity in Sun Valley

This chart illustrates the average monthly humidity levels in Sun Valley, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Sun Valley is approximately 41%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%87%84%78%64%56%44%34%41%60%81%82%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Sun Valley

In Sun Valley in September, the maximum UV index reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check the Hourly UV Index in Sun Valley.

Maximum UV Index Levels in Sun Valley for September

The chart shows the monthly maximum UV Index (UVI) for Sun Valley 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. In September, the maximum UV index in Sun Valley typically reaches 10, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec46891112121110743
Data source: Sun Valley 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.

How September Weather in Sun Valley Compares to Other Months

Weather in Sun Valley varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Sun Valley, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Sun Valley, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather0°C (33°F)91 mm (3.6 inches)85%moderate
February Weather1°C (34°F)87 mm (3.4 inches)87%high
March Weather3°C (38°F)71 mm (2.8 inches)84%very high
April Weather8°C (47°F)32 mm (1.3 inches)78%very high
May Weather13°C (55°F)39 mm (1.5 inches)64%extreme
June Weather19°C (67°F)8 mm (0.3 inches)56%extreme
July Weather24°C (75°F)11 mm (0.4 inches)44%extreme
August Weather23°C (73°F)11 mm (0.4 inches)34%extreme
September Weather18°C (64°F)8 mm (0.3 inches)41%very high
October Weather10°C (51°F)33 mm (1.3 inches)60%high
November Weather5°C (42°F)39 mm (1.5 inches)81%moderate
December Weather0°C (32°F)64 mm (2.5 inches)82%moderate

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