Sumas, WA climate
Sumas has mild winters and pleasant summers, with plenty of rain. A typical July afternoon reaches 76°, a January night drops to 33°, and about 11 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Sumas feels like
Winter
Spring
Summer
Fall
Sumas weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 44° | 33° | 9.0" | 3.1" | 18 | 31° – 44° |
| February | 48° | 34° | 5.1" | 2.7" | 15 | 32° – 47° |
| March | 53° | 37° | 6.3" | 1.0" | 19 | 39° – 50° |
| April | 59° | 41° | 4.9" | 0.1" | 16 | 45° – 56° |
| May | 66° | 47° | 3.6" | 0 | 12 | 52° – 60° |
| June | 70° | 51° | 3.0" | 0 | 12 | 57° – 66° |
| July | 76° | 54° | 1.8" | 0 | 6 | 61° – 69° |
| August | 76° | 54° | 1.8" | 0 | 6 | 61° – 68° |
| September | 70° | 50° | 3.4" | 0 | 9 | 57° – 63° |
| October | 59° | 44° | 6.8" | 0 | 16 | 49° – 56° |
| November | 49° | 38° | 9.9" | 1.3" | 19 | 39° – 49° |
| December | 43° | 33° | 8.1" | 2.6" | 19 | 33° – 42° |
| Year | 59° | 43° | 63.6" | 10.8" | 168 |
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain and snow in Sumas
Sumas gets 64 inches of rain and melted snow a year. November is the wettest month and July the driest. Rain or snow falls on about 168 days a year.
About 185 frost-free days a year
In half of years the last 32° night comes by April 18 and the first one by October 18. That leaves about 185 frost-free days for gardens, longer than 58% of U.S. towns.
Heating and cooling a home in Sumas
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Sumas, 99% of that work is heating and 1% is cooling, so the furnace matters far more than the air conditioner.
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
How Sumas compares
Compared with every U.S. town and city on TownTapestry, each counted once.
Warmer than it used to be
The last 30 years in Sumas averaged 1.4° warmer than the 1900s. The biggest change is in January (+3.1°). The shift is larger than in 67% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Sumas’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. February swings the most: between 1991 and 2020 its average temperature ranged from 32° to 47°. September is the most reliable, staying within 6°.
Common questions about Sumas’s climate
What is the coldest month in Sumas?
January, with a typical high of 44° and a low of 33°.
What is the hottest month in Sumas?
August, with a typical high of 76° and a low of 54°. About 2 days a year reach 90°.
How much snow does Sumas get?
About 11 inches in a normal winter, most of it in January.
When is the first frost in Sumas?
In half of years the first 32° night comes by October 18, and the last spring frost by April 18.
What is the rainiest month in Sumas?
November, with 9.9 inches of rain and melted snow. The year totals 64 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Sumas itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Clearbrook, WA (3 mi) away. Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.