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Monthly climate in Mercer Island, Washington, United States

Last updated: May 6, 2024

Under the Köppen–Geiger climate classification Mercer Island features a warm-summer Mediterranean climate (Csb).Temperatures typically range between 5 °C (41 °F) and 19 °C (67 °F) through the year, but rarely can drop to -10 °C (14 °F) or can rise to as high as 38 °C (101 °F).The average annual precipitation amounts to about 1394 mm (54.9 inches) and receives 161 rainy days on the 1 mm (0.04 inches) threshold annually.Mercer Island enjoys an average of 2583 hours of sunshine throughout the year, and daylight varies from 8 hours 30 minutes to 15 hours 52 minutes per day.

Monthly average temperatures in Mercer Island, Washington, United States §

The warmest months in Mercer Island are June, July and August, with daily mean temperatures ranging from 17 to 19 °C (62 - 67 °F) throughout the day. The coldest temperatures usually occur in January, February and December, when daily mean temperatures range from 5 to 6 °C (41 - 43 °F) throughout the day. On average each year, Mercer Island experiences 28 days above 25 °C (77.0 °F) and 11 days below 0 °C (32.0 °F).

Monthly average temperatures with daily means, minimums and maximums for period, average high and low temperatures in Mercer Island, Washington, United States.Generated using Copernicus Climate Change Service information.Data for period from January 2017 to June 2022.
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Maximum 14°C
(57°F)		 14°C
(58°F)		 22°C
(72°F)		 24°C
(75°F)		 28°C
(82°F)		 38°C
(101°F)		 32°C
(91°F)		 33°C
(93°F)		 30°C
(86°F)		 23°C
(74°F)		 17°C
(63°F)		 14°C
(58°F)
Mean maximum 13°C
(55°F)		 12°C
(54°F)		 17°C
(63°F)		 21°C
(70°F)		 25°C
(78°F)		 29°C
(84°F)		 30°C
(87°F)		 31°C
(88°F)		 28°C
(82°F)		 20°C
(68°F)		 16°C
(61°F)		 12°C
(55°F)
Average high 8°C
(47°F)		 8°C
(46°F)		 11°C
(52°F)		 14°C
(57°F)		 18°C
(64°F)		 21°C
(70°F)		 24°C
(76°F)		 24°C
(76°F)		 21°C
(69°F)		 15°C
(59°F)		 11°C
(52°F)		 8°C
(46°F)
Daily mean 6°C
(43°F)		 5°C
(41°F)		 7°C
(46°F)		 10°C
(50°F)		 14°C
(57°F)		 17°C
(62°F)		 19°C
(67°F)		 19°C
(67°F)		 16°C
(62°F)		 11°C
(52°F)		 8°C
(47°F)		 6°C
(42°F)
Average low 4°C
(39°F)		 3°C
(37°F)		 5°C
(40°F)		 7°C
(44°F)		 10°C
(50°F)		 13°C
(55°F)		 15°C
(59°F)		 15°C
(59°F)		 13°C
(55°F)		 8°C
(47°F)		 6°C
(43°F)		 4°C
(39°F)
Mean minimum -3°C
(28°F)		 -4°C
(25°F)		 0°C
(32°F)		 2°C
(36°F)		 6°C
(43°F)		 9°C
(48°F)		 12°C
(54°F)		 11°C
(53°F)		 9°C
(48°F)		 3°C
(37°F)		 1°C
(33°F)		 -3°C
(27°F)
Minimum -7°C
(19°F)		 -10°C
(14°F)		 -1°C
(31°F)		 1°C
(34°F)		 5°C
(42°F)		 8°C
(46°F)		 11°C
(52°F)		 10°C
(51°F)		 8°C
(46°F)		 -1°C
(30°F)		 -1°C
(30°F)		 -7°C
(20°F)

Compare climate in Mercer Island with other places

Compare temperature, precipitation, sunshine, UV index in Mercer Island, Washington, United States with other places around the world.

Monthly average precipitation in Mercer Island, Washington, United States §

Mercer Island usually has the most precipitation in February, November and December, with an average of 18 rainy days and 185 mm (7.3 inches) of precipitation per month.The driest months in Mercer Island are June, July and August. On average, 32 mm (1.3 inches) of precipitation falls during these months.

Monthly average precipitation and precipitation days in Mercer Island, Washington, United States.Generated using Copernicus Climate Change Service information.Data for period from January 2017 to January 2022.
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Average precipitation mm (inches) 175 (6.9) 177 (7.0) 126 (4.9) 117 (4.6) 68 (2.7) 63 (2.5) 18 (0.7) 16 (0.6) 100 (3.9) 155 (6.1) 181 (7.1) 196 (7.7)
Average precipitation days (≥ 1 mm) 16 19 17 14 12 9 5 5 12 15 18 19

Monthly sunshine hours in Mercer Island, Washington, United States §

The sunniest months in Mercer Island are June, July and August, when the sun shines an average of 10 hours 52 minutes a day.Least sunny months in Mercer Island: January, November and December receive an average of 3 hours 7 minutes of sunshine daily.

Mean monthly sunshine duration, average sunshine hours per day and mean daily daylight hours in Mercer Island, Washington, United States.Generated using Copernicus Atmosphere Monitoring Service information.Data for period from January 2017 to January 2022.
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Mean monthly sunshine hours 80 123 199 229 299 310 360 329 254 189 114 92
Mean daily daylight hours 8h 56m 10h 16m 11h 57m 13h 40m 15h 8m 15h 52m 15h 27m 14h 8m 12h 29m 10h 47m 9h 17m 8h 30m

Solar UV radiation in Mercer Island, Washington, United States §

Mercer Island experiences the highest level of ultraviolet (UV) radiation in June, July and August, when the maximum UV index can reach values of 8 - 9, which corresponds to the Very High category of sun exposure.January, November and December are in the Low exposure category. In these months, the maximum values of the UV index do not exceed 2. For more detailed information, check out our hourly Mercer Island UV Index data.

Average daily maximum UV levels by month for Mercer Island, Washington, United States.Generated using Copernicus Atmosphere Monitoring Service information.Data for period from January 2022 to January 2023.
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
UV Index (month maximum) 2 3 5 6 8 9 9 8 7 5 2 1