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Monthly climate in Sumas, Washington, United States

Last updated: May 6, 2024

Under the Köppen–Geiger climate classification Sumas features a oceanic climate (Cfb).Temperatures typically range between 2 °C (35 °F) and 18 °C (64 °F) through the year, but rarely can drop to -18 °C (0 °F) or can rise to as high as 39 °C (102 °F).The average annual precipitation amounts to about 2050 mm (80.7 inches) and receives 169 rainy days on the 1 mm (0.04 inches) threshold annually.Sumas enjoys an average of 2673 hours of sunshine throughout the year, and daylight varies from 8 hours 16 minutes to 16 hours 7 minutes per day.

Monthly average temperatures in Sumas, Washington, United States §

The warmest months in Sumas are June, July and August, with daily mean temperatures ranging from 15 to 18 °C (59 - 64 °F) throughout the day. The coldest temperatures usually occur in January, February and December, when daily mean temperatures range from 2 to 3 °C (35 - 37 °F) throughout the day. On average each year, Sumas experiences 21 days above 25 °C (77.0 °F) and 55 days below 0 °C (32.0 °F).

Monthly average temperatures with daily means, minimums and maximums for period, average high and low temperatures in Sumas, 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 11°C
(52°F)		 12°C
(54°F)		 23°C
(74°F)		 25°C
(78°F)		 27°C
(81°F)		 39°C
(102°F)		 33°C
(91°F)		 35°C
(94°F)		 33°C
(91°F)		 23°C
(74°F)		 14°C
(58°F)		 12°C
(54°F)
Mean maximum 10°C
(49°F)		 10°C
(50°F)		 16°C
(60°F)		 20°C
(69°F)		 24°C
(76°F)		 28°C
(82°F)		 30°C
(86°F)		 32°C
(90°F)		 28°C
(82°F)		 18°C
(65°F)		 13°C
(57°F)		 10°C
(50°F)
Average high 5°C
(42°F)		 5°C
(41°F)		 9°C
(49°F)		 12°C
(55°F)		 17°C
(62°F)		 19°C
(66°F)		 22°C
(72°F)		 23°C
(73°F)		 19°C
(66°F)		 12°C
(55°F)		 8°C
(47°F)		 5°C
(40°F)
Daily mean 3°C
(37°F)		 2°C
(35°F)		 5°C
(41°F)		 8°C
(47°F)		 12°C
(54°F)		 15°C
(59°F)		 17°C
(63°F)		 18°C
(64°F)		 14°C
(58°F)		 9°C
(48°F)		 5°C
(42°F)		 2°C
(36°F)
Average low 0°C
(33°F)		 -1°C
(31°F)		 2°C
(35°F)		 4°C
(39°F)		 8°C
(46°F)		 10°C
(51°F)		 12°C
(54°F)		 13°C
(55°F)		 11°C
(51°F)		 5°C
(42°F)		 3°C
(37°F)		 -0°C
(32°F)
Mean minimum -8°C
(18°F)		 -8°C
(18°F)		 -6°C
(22°F)		 -1°C
(30°F)		 3°C
(38°F)		 6°C
(43°F)		 9°C
(48°F)		 8°C
(47°F)		 6°C
(43°F)		 -0°C
(32°F)		 -3°C
(27°F)		 -9°C
(16°F)
Minimum -14°C
(7°F)		 -11°C
(12°F)		 -8°C
(18°F)		 -5°C
(24°F)		 2°C
(36°F)		 5°C
(42°F)		 8°C
(46°F)		 7°C
(44°F)		 5°C
(40°F)		 -3°C
(28°F)		 -4°C
(25°F)		 -18°C
(0°F)

Compare climate in Sumas with other places

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

Monthly average precipitation in Sumas, Washington, United States §

Sumas usually has the most precipitation in January, November and December, with an average of 18 rainy days and 275 mm (10.8 inches) of precipitation per month.The driest months in Sumas are June, July and August. On average, 51 mm (2.0 inches) of precipitation falls during these months.

Monthly average precipitation and precipitation days in Sumas, 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) 240 (9.4) 214 (8.4) 197 (7.8) 162 (6.4) 103 (4.0) 82 (3.2) 44 (1.8) 27 (1.1) 166 (6.5) 229 (9.0) 317 (12.5) 269 (10.6)
Average precipitation days (≥ 1 mm) 16 19 17 17 12 11 6 5 12 16 19 19

Monthly sunshine hours in Sumas, Washington, United States §

The sunniest months in Sumas are June, July and August, when the sun shines an average of 11 hours 30 minutes a day.Least sunny months in Sumas: January, November and December receive an average of 3 hours 11 minutes of sunshine daily.

Mean monthly sunshine duration, average sunshine hours per day and mean daily daylight hours in Sumas, 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 81 138 200 232 326 332 383 343 247 174 118 94
Mean daily daylight hours 8h 44m 10h 10m 11h 56m 13h 46m 15h 19m 16h 7m 15h 40m 14h 16m 12h 31m 10h 43m 9h 6m 8h 16m

Solar UV radiation in Sumas, Washington, United States §

Sumas 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 Sumas UV Index data.

Average daily maximum UV levels by month for Sumas, 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 7 8 9 8 6 4 2 1