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September Weather in Merrillan, United States

Last updated: June 24, 2025

In September, the average temperature in Merrillan, United States is a comfortable 17°C (63°F). However, temperatures can vary significantly, with minimums plunging to 1°C (34°F) and maximums soaring up to 33°C (92°F). Expect about 97 mm (3.8 in) of precipitation spread over 10 days, and be prepared for a high average humidity of 80%.

September Temperature in Merrillan

In September in Merrillan, the average temperature is 17°C (63°F). Maximum temperatures can reach up to 33°C (92°F), while minimums can drop as low as 1°C (34°F). This variation in temperature makes it essential to pack a versatile wardrobe for your travels.

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

The chart illustrates September temperature patterns in Merrillan, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Merrillan, September typically has an average temperature of 17°C (63°F), with highs reaching up to 33°C (92°F) and lows dropping to around 1°C (34°F).
JanFebMarAprMayJunJulAugSepOctNovDec181934445869726963483425
Data source: Temperature data for Merrillan 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 Merrillan

In Merrillan in September, the total precipitation amount is 97 mm (3.8 in) over a span of 10 days.

September Precipitation Trends in Merrillan

The chart displays monthly precipitation patterns in Merrillan, 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 Merrillan, September typically receives around 97 mm (3.8 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec33525695130135112136971195350
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Merrillan

In Merrillan in September humidity is 80%. With an average temperature of 17°C (63°F), this humidity feels like you're walking through a thick, warm blanket, making travel feel slightly stifling and requiring frequent breaks to stay comfortable.

September Average Humidity in Merrillan

This chart illustrates the average monthly humidity levels in Merrillan, 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 Merrillan is approximately 80%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec88%89%86%85%79%80%80%78%80%84%89%85%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Merrillan

In Merrillan in September, the maximum UV index is 7, which corresponds to the high Exposure Category. This means that the time to burn is approximately 25 minutes. For more detailed information, you can check the Hourly UV Index in Merrillan.

Maximum UV Index Levels in Merrillan for September

The chart shows the monthly maximum UV Index (UVI) for Merrillan 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 Merrillan typically reaches 7, which falls under the high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec24588101097532
Data source: Merrillan 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 Merrillan Compares to Other Months

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

This table compares monthly weather conditions in Merrillan, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-8°C (18°F)33 mm (1.3 inches)88%low
February Weather-7°C (19°F)52 mm (2.1 inches)89%moderate
March Weather1°C (34°F)56 mm (2.2 inches)86%moderate
April Weather6°C (44°F)95 mm (3.8 inches)85%very high
May Weather15°C (58°F)130 mm (5.1 inches)79%very high
June Weather20°C (69°F)135 mm (5.3 inches)80%very high
July Weather22°C (73°F)112 mm (4.4 inches)80%very high
August Weather20°C (69°F)136 mm (5.4 inches)78%very high
September Weather17°C (63°F)97 mm (3.8 inches)80%high
October Weather9°C (49°F)119 mm (4.7 inches)84%moderate
November Weather1°C (34°F)53 mm (2.1 inches)89%moderate
December Weather-4°C (25°F)50 mm (2.0 inches)85%low

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