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December Weather in SeaTac, United States

Last updated: June 24, 2025

In December, the average temperature in SeaTac, United States hovers around 6°C (42°F). Expect minimums to drop as low as -7°C (20°F), while the maximums can reach up to 14°C (58°F). With an average precipitation of 196 mm (7.7 in) spread over 19 days, and a notable humidity level at 88%, be prepared for a distinctly chilly and damp experience.

December Temperature in SeaTac

In December in SeaTac, the average temperature is 6°C (42°F), with maximums reaching 14°C (58°F) and minimums dipping as low as -7°C (20°F). Travelers should be prepared for a range of temperatures and pack accordingly to enjoy their visit.

December Weather in SeaTac: Daily Temperature Highs, Lows, and Averages

The chart illustrates December temperature patterns in SeaTac, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In SeaTac, December typically has an average temperature of 6°C (42°F), with highs reaching up to 14°C (58°F) and lows dropping to around -7°C (20°F).
JanFebMarAprMayJunJulAugSepOctNovDec424145505762666762524742
Data source: Temperature data for SeaTac 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.

December Precipitation in SeaTac

In SeaTac in December, the precipitation amount is 196 mm (7.7 in) over the course of 19 days.

December Precipitation Trends in SeaTac

The chart displays monthly precipitation patterns in SeaTac, with values for each month alongside December’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how December’s conditions compare to those of other months. In SeaTac, December typically receives around 196 mm (7.7 inches) of precipitation spread over approximately 19 days.
JanFebMarAprMayJunJulAugSepOctNovDec17517712611768631916100155181196
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in SeaTac

In SeaTac in December, humidity is 88%. With an average temperature of 6°C (42°F), this humidity feels like a damp chill that seeps into your bones, making traveling uncomfortable as the cold air clings to your skin and saps your energy.

December Average Humidity in SeaTac

This chart illustrates the average monthly humidity levels in SeaTac, with December’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In December, average humidity in SeaTac is approximately 88%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec86%86%87%84%81%82%79%63%62%83%89%88%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in SeaTac

In SeaTac in December, the maximum UV index is 1, which corresponds to a low Exposure Category. This means you have a time to burn of 45 minutes. For more details, you can check the Hourly UV Index in SeaTac.

Maximum UV Index Levels in SeaTac for December

The chart shows the monthly maximum UV Index (UVI) for SeaTac in December, 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 December, the maximum UV index in SeaTac typically reaches 1, which falls under the low exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec235689987521
Data source: SeaTac December 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 December Weather in SeaTac Compares to Other Months

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

This table compares monthly weather conditions in SeaTac, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather6°C (43°F)175 mm (6.9 inches)86%low
February Weather5°C (41°F)177 mm (7.0 inches)86%moderate
March Weather7°C (46°F)126 mm (4.9 inches)87%moderate
April Weather10°C (50°F)117 mm (4.6 inches)84%high
May Weather14°C (57°F)68 mm (2.7 inches)81%very high
June Weather17°C (62°F)63 mm (2.5 inches)82%very high
July Weather19°C (67°F)18 mm (0.7 inches)79%very high
August Weather19°C (67°F)16 mm (0.6 inches)63%very high
September Weather16°C (62°F)100 mm (3.9 inches)62%high
October Weather11°C (52°F)155 mm (6.1 inches)83%moderate
November Weather8°C (47°F)181 mm (7.1 inches)89%low
December Weather6°C (42°F)196 mm (7.7 inches)88%low

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