Climate - Seattle (Washington_state)

In Seattle, the climate is sub-oceanic, with quite mild, rainy winters and mild, fairly sunny summers.
The city is located in northwestern United States, in the state of Washington, of which it is the largest city. Although it is surrounded by water, since it lies between the Puget Sound and Lake Washington, Seattle is still 150 kilometers (95 miles) away from the Pacific coast, and it is partially protected by the mountains of the Coastal Chain which lie to the west (where the Olympic National Park is located), so it is less humid than the coastal area (where rainfall is equal to or higher than 2,000 millimeters - 80 inches per year).
And although it is famous in the United States for being damp and cloudy, in summer, when it is protected by the high pressure system of the Pacific, there are many sunny days. However, the rains in the cold half-year are frequent, and often occur in the form of drizzle.
The average temperature of December (which in western United States is often the coldest month) is 5.6 °C (42 °F), that of August is 19.6 °C (67.4 °F). Here are the average temperatures at the Tacoma airport.

Although winter is mild enough, there can sometimes be cold waves, sometimes even in November, with lows going down to -10 °C (14 °F) or even below. The coldest record is -17.8 °C (0 °F) and was set in January 1950.
Snow in Seattle is rare: on average, 16 centimeters (6.3 in) of snow fall per year. However, occasionally there is a moderate snowfall. Two particularly snowy months were February 2019, with 50 cm (20 in) in total, and January 1969, with as much as 127 cm (50 in). In December 2008, snow remained on the ground for more than 10 days in a row. In February 2021, 28 cm (11 in) of snow fell in two days.
In summer, daytime temperatures are generally mild or pleasantly warm. However, there may also be heat waves, which last a few days, with highs around 35 °C (95 °F), and sometimes more. During the exceptional heat wave of late June 2021, it reached 42.2 (108 °F).
Precipitation amounts to 1,000 mm (39.4 in) per year. It is more abundant from November to January, and in any case, it is frequent from October to May. However, as we have said, in summer it is reduced: the summer, in July and August, is pleasant, with cool nights, and quite sunny, with some morning fogs. Here is the average rainfall.

About 2,100 hours of sunshine per year are recorded in Seattle. As mentioned, even though the sky is often cloudy for many months a year, in summer (and even in late spring) the sunshine amount becomes good. Here are the average sunshine hours per day.

In Seattle, the sea is cold all year round, as can be seen in the following table.



Around Seattle, we find very snowy mountains. To the west, we find the aforementioned mountains of the Olympic National Park. About 100 km (62 mi) to the south-east, we find Mount Rainier, a volcano, 4,392 meters (14,411 feet) high, which is the snowiest place in the United States. North-east of Seattle, the Cascade Range (see for example the Mount Baker Ski Area) is very wet as well, and snowy in the winter months.

Best Time

The best time to visit Seattle is summer, especially in July and August, since it is the mildest, driest and sunniest period of the year. May, June and September are also acceptable months.

Back to the climate of Washington state.

Seattle - Weather by month

Based on the period 1991-2020

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In January, the weather in Seattle is usually quite cold. The average temperature is of 6.0 °C (43 °F), with a minimum of 3.2 °C (37.8 °F) and a maximum of 8.9 °C (48 °F).
On the coldest nights of the month, the temperature usually drops to around -3.5 °C (25.5 °F). However, it dropped to -9.4 °C (15.1 °F) in January 1996.
On the warmest days of the month, the temperature usually reaches around 14 °C (57 °F). However, it reached 17.8 °C (64 °F) in January 2018.
Precipitation amounts to 145 mm (5.7 in), distributed over 19 days.
The day lasts on average 9 hours and 0 minutes.
There are on average 2.5 hours of sunshine per day. So, the sun shines 25% of the time.
The average humidity is 80%. Hence, the air is normally humid.
The average wind speed is 13 kph (8 mph).
The average sea temperature is of 8 °C (46.5 °F). Therefore, the sea is very cold for swimming.

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In February, the weather in Seattle is usually quite mild. The average temperature is of 6.7 °C (44 °F), with a minimum of 3.2 °C (37.8 °F) and a maximum of 10.2 °C (50.4 °F).
On the coldest nights of the month, the temperature usually drops to around -2.5 °C (27.5 °F). However, it dropped to -7.2 °C (19 °F) in February 2011.
On the warmest days of the month, the temperature usually reaches around 15 °C (59.5 °F). However, it reached 19.4 °C (66.9 °F) in February 1992.
Precipitation amounts to 95 mm (3.7 in), distributed over 16 days.
The day lasts on average 10 hours and 20 minutes.
There are on average 4 hours of sunshine per day. So, the sun shines 38% of the time.
The average humidity is 76%. Hence, the air is normally humid.
The average wind speed is 13 kph (8 mph).
The average sea temperature is of 8 °C (46.5 °F). Therefore, the sea is very cold for swimming.

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In March, the weather in Seattle is usually quite mild. The average temperature is of 8.4 °C (47 °F), with a minimum of 4.4 °C (39.9 °F) and a maximum of 12.3 °C (54.1 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around -0.5 °C (31 °F). However, it dropped to -3.3 °C (26.1 °F) in March 2009.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 19.5 °C (66.5 °F). However, it reached 26.1 °C (79 °F) in March 2019.
Precipitation amounts to 105 mm (4.1 in), distributed over 17 days.
The day lasts on average 12 hours and 0 minutes.
There are on average 6 hours of sunshine per day. So, the sun shines 48% of the time.
The average humidity is 74%. Hence, the air is normally humid.
The average wind speed is 14 kph (9 mph).
The average sea temperature is of 8.5 °C (47 °F). Therefore, the sea is very cold for swimming.

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In April, the weather in Seattle is usually mild. The average temperature is of 10.8 °C (51 °F), with a minimum of 6.3 °C (43.3 °F) and a maximum of 15.2 °C (59.4 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 2 °C (35.5 °F). However, it dropped to 0 °C (32 °F) in April 2008.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 23.5 °C (74.5 °F). However, it reached 31.7 °C (89.1 °F) in April 2016.
Precipitation amounts to 80 mm (3.1 in), distributed over 15 days.
The day lasts on average 13 hours and 40 minutes.
There are on average 7 hours of sunshine per day. So, the sun shines 51% of the time.
The average humidity is 71%. Hence, the air is normally humid.
The average wind speed is 13 kph (8 mph).
The average sea temperature is of 9 °C (48.5 °F). Therefore, the sea is very cold for swimming.

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In May, the weather in Seattle is usually mild. The average temperature is of 14.2 °C (58 °F), with a minimum of 9.3 °C (48.7 °F) and a maximum of 19.1 °C (66.4 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 4.5 °C (40.5 °F). However, it dropped to 2 °C (35.6 °F) in May 1999.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 28 °C (82 °F). However, it reached 32.2 °C (90 °F) in May 2008.
Precipitation amounts to 50 mm (2 in), distributed over 11 days.
The day lasts on average 15 hours and 10 minutes. So the days are long.
There are on average 8 hours of sunshine per day. So, the sun shines 54% of the time.
The average humidity is 68%.
The average wind speed is 12 kph (8 mph).
The average sea temperature is of 10.5 °C (51 °F). Therefore, the sea is very cold for swimming.

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In June, the weather in Seattle is usually very mild. The average temperature is of 16.7 °C (62 °F), with a minimum of 11.7 °C (53.1 °F) and a maximum of 21.7 °C (71.1 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 8 °C (46.5 °F). However, it dropped to 5.6 °C (42.1 °F) in June 1991.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 30 °C (85.5 °F). However, it reached 35.6 °C (96.1 °F) in June 2017.
Precipitation amounts to 35 mm (1.4 in), distributed over 9 days.
The day lasts on average 15 hours and 55 minutes. So the days are long. June 21, the summer solstice, is the longest day of the year in the Northern Hemisphere.
There are on average 9 hours of sunshine per day. So, the sun shines 56% of the time.
The average humidity is 67%.
The average wind speed is 12 kph (8 mph).
The average sea temperature is of 12 °C (53.5 °F). Therefore, the sea is very cold for swimming.

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In July, the weather in Seattle is usually warm. The average temperature is of 19.5 °C (67 °F), with a minimum of 13.8 °C (56.8 °F) and a maximum of 25.2 °C (77.4 °F).
On the coldest nights of the month, the temperature usually drops to around 11 °C (51.5 °F). However, it dropped to 8.9 °C (48 °F) in July 1999.
On the warmest days of the month, the temperature usually reaches around 33 °C (91.5 °F). However, it reached 39.4 °C (102.9 °F) in July 2009.
Precipitation amounts to 15 mm (0.6 in), distributed over 5 days.
The day lasts on average 15 hours and 30 minutes. So the days are long.
There are on average 10 hours of sunshine per day. So, the sun shines 65% of the time.
The average humidity is 64%.
The average wind speed is 11 kph (7 mph).
The average sea temperature is of 13 °C (55.5 °F). Therefore, the sea is very cold for swimming.

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In August, the warmest month of the year, the weather in Seattle is usually warm. The average temperature is of 19.6 °C (67 °F), with a minimum of 14 °C (57.2 °F) and a maximum of 25.3 °C (77.5 °F).
On the coldest nights of the month, the temperature usually drops to around 11 °C (51.5 °F). However, it dropped to 8.9 °C (48 °F) in August 1993.
On the warmest days of the month, the temperature usually reaches around 32 °C (90 °F). However, it reached 36.7 °C (98.1 °F) in August 2020.
Precipitation amounts to 25 mm (1 in), distributed over 5 days.
The day lasts on average 14 hours and 5 minutes. So the days are long.
There are on average 9 hours of sunshine per day. So, the sun shines 64% of the time.
The average humidity is 65%.
The average wind speed is 11 kph (7 mph).
The average sea temperature is of 13.5 °C (56 °F). Therefore, the sea is very cold for swimming.

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In September, the weather in Seattle is usually very mild. The average temperature is of 17 °C (63 °F), with a minimum of 12 °C (53.6 °F) and a maximum of 22 °C (71.6 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around 7.5 °C (45.5 °F). However, it dropped to 5.6 °C (42.1 °F) in September 1999.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 29 °C (84 °F). However, it reached 33.9 °C (93 °F) in September 2013.
Precipitation amounts to 40 mm (1.6 in), distributed over 8 days.
The day lasts on average 12 hours and 30 minutes.
There are on average 7.5 hours of sunshine per day. So, the sun shines 59% of the time.
The average humidity is 70%. Hence, the air is normally humid.
The average wind speed is 11 kph (7 mph).
The average sea temperature is of 13 °C (55 °F). Therefore, the sea is very cold for swimming.

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In October, the weather in Seattle is usually mild. The average temperature is of 12.0 °C (54 °F), with a minimum of 8.3 °C (46.9 °F) and a maximum of 15.8 °C (60.4 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around 2.5 °C (37 °F). However, it dropped to -1.1 °C (30 °F) in October 1991.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 22.5 °C (72.5 °F). However, it reached 28.3 °C (82.9 °F) in October 1991.
Precipitation amounts to 100 mm (3.9 in), distributed over 14 days.
The day lasts on average 10 hours and 50 minutes.
There are on average 4.5 hours of sunshine per day. So, the sun shines 42% of the time.
The average humidity is 78%. Hence, the air is normally humid.
The average wind speed is 11 kph (7 mph).
The average sea temperature is of 11 °C (52 °F). Therefore, the sea is very cold for swimming.

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In November, the weather in Seattle is usually quite mild. The average temperature is of 8.0 °C (46 °F), with a minimum of 4.9 °C (40.8 °F) and a maximum of 11.2 °C (52.2 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around -1.5 °C (29 °F). However, it dropped to -10 °C (14 °F) in November 2010.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 17 °C (62 °F). However, it reached 23.3 °C (73.9 °F) in November 2010.
Precipitation amounts to 160 mm (6.3 in), distributed over 18 days.
The day lasts on average 9 hours and 20 minutes.
There are on average 2.5 hours of sunshine per day. So, the sun shines 26% of the time.
The average humidity is 80%. Hence, the air is normally humid.
The average wind speed is 13 kph (8 mph).
The average sea temperature is of 9.5 °C (49.5 °F). Therefore, the sea is very cold for swimming.

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In December, the coldest month of the year, the weather in Seattle is usually quite cold. The average temperature is of 5.6 °C (42 °F), with a minimum of 2.8 °C (37 °F) and a maximum of 8.3 °C (46.9 °F).
On the coldest nights of the month, the temperature usually drops to around -4 °C (25 °F). However, it dropped to -10 °C (14 °F) in December 2008.
On the warmest days of the month, the temperature usually reaches around 14 °C (57 °F). However, it reached 18.9 °C (66 °F) in December 2014.
Precipitation amounts to 145 mm (5.7 in), distributed over 18 days.
The day lasts on average 8 hours and 30 minutes. December 21, the winter solstice, is the shortest day of the year in the Northern Hemisphere.
There are on average 1.5 hours of sunshine per day. So, the sun shines 20% of the time.
The average humidity is 80%. Hence, the air is normally humid.
The average wind speed is 14 kph (8 mph).
The average sea temperature is of 8.5 °C (47.5 °F). Therefore, the sea is very cold for swimming.