Average Weather in Sumas Washington, United States
In Sumas, the summers are warm and partly cloudy and the winters are very cold, wet, and mostly cloudy. Over the course of the year, the temperature typically varies from 34°F to 79°F and is rarely below 22°F or above 89°F.
Based on the tourism score, the best time of year to visit Sumas for warm-weather activities is from mid July to late August.
The warm season lasts for 3.0 months, from June 19 to September 17, with an average daily high temperature above 71°F. The hottest day of the year is August 3, with an average high of 79°F and low of 56°F.
The cool season lasts for 3.2 months, from November 14 to February 19, with an average daily high temperature below 49°F. The coldest day of the year is December 30, with an average low of 34°F and high of 42°F.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
In Sumas, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in Sumas begins around June 15 and lasts for 3.6 months, ending around October 1. On August 3, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 71% of the time, and overcast or mostly cloudy 29% of the time.
The cloudier part of the year begins around October 1 and lasts for 8.4 months, ending around June 15. On December 11, the cloudiest day of the year, the sky is overcast or mostly cloudy 74% of the time, and clear, mostly clear, or partly cloudy 26% of the time.
Cloud Cover Categories
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Sumas varies significantly throughout the year.
The wetter season lasts 6.5 months, from October 8 to April 23, with a greater than 36% chance of a given day being a wet day. The chance of a wet day peaks at 61% on November 16.
The drier season lasts 5.5 months, from April 23 to October 8. The smallest chance of a wet day is 11% on August 6.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 59% on November 16.
Daily Chance of Precipitation
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Sumas experiences extreme seasonal variation in monthly rainfall.
Rain falls throughout the year in Sumas. The most rain falls during the 31 days centered around November 18, with an average total accumulation of 8.5 inches.
The least rain falls around August 1, with an average total accumulation of 1.0 inches.
Average Monthly Rainfall
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Sumas experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 3.7 months, from November 17 to March 8, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around January 3, with an average total liquid-equivalent accumulation of 0.4 inches.
The snowless period of the year lasts for 8.3 months, from March 8 to November 17. The least snow falls around July 12, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in Sumas varies extremely over the course of the year. In 2019, the shortest day is December 21, with 8 hours, 14 minutes of daylight; the longest day is June 21, with 16 hours, 12 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:04 AM on June 16, and the latest sunrise is 2 hours, 59 minutes later at 8:03 AM on December 31. The earliest sunset is at 4:11 PM on December 11, and the latest sunset is 5 hours, 6 minutes later at 9:17 PM on June 25.
Daylight saving time (DST) is observed in Sumas during 2019, starting in the spring on March 10, lasting 7.8 months, and ending in the fall on November 3.
Sunrise & Sunset with Twilight and Daylight Saving Time
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
The perceived humidity level in Sumas, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, staying within 1% of 1% throughout.
Humidity Comfort Levels
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in Sumas experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 5.6 months, from October 19 to April 7, with average wind speeds of more than 4.0 miles per hour. The windiest day of the year is December 5, with an average hourly wind speed of 5.2 miles per hour.
The calmer time of year lasts for 6.4 months, from April 7 to October 19. The calmest day of the year is August 9, with an average hourly wind speed of 2.9 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Sumas varies throughout the year.
The wind is most often from the south for 8.2 months, from March 12 to November 19, with a peak percentage of 51% on June 10. The wind is most often from the east for 3.8 months, from November 19 to March 12, with a peak percentage of 56% on January 1.
Sumas is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average water temperature experiences some seasonal variation over the course of the year.
The time of year with warmer water lasts for 3.0 months, from June 17 to September 17, with an average temperature above 56°F. The day of the year with the warmest water is August 2, with an average temperature of 59°F.
The time of year with cooler water lasts for 4.5 months, from November 23 to April 7, with an average temperature below 48°F. The day of the year with the coolest water is January 29, with an average temperature of 45°F.
Average Water Temperature
Best Time of Year to Visit
To characterize how pleasant the weather is in Sumas throughout the year, we compute two travel scores.
The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Sumas for general outdoor tourist activities is from mid July to late August, with a peak score in the first week of August.
The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Sumas for hot-weather activities is from mid July to mid August, with a peak score in the first week of August.
For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.
Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.
Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.
Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.
Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.
Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).
The growing season in Sumas typically lasts for 7.9 months (241 days), from around March 15 to around November 11, rarely starting before February 20 or after April 7, and rarely ending before October 19 or after December 12.
Time Spent in Various Temperature Bands and the Growing Season
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.
Based on growing degree days alone, the first spring blooms in Sumas should appear around April 19, only rarely appearing before April 3 or after May 4.
Growing Degree Days
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy experiences extreme seasonal variation over the course of the year.
The brighter period of the year lasts for 3.3 months, from May 13 to August 21, with an average daily incident shortwave energy per square meter above 5.5 kWh. The brightest day of the year is July 21, with an average of 6.6 kWh.
The darker period of the year lasts for 3.9 months, from October 22 to February 19, with an average daily incident shortwave energy per square meter below 2.0 kWh. The darkest day of the year is December 25, with an average of 0.8 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Sumas are 49.000 deg latitude, -122.265 deg longitude, and 49 ft elevation.
The topography within 2 miles of Sumas contains only modest variations in elevation, with a maximum elevation change of 203 feet and an average elevation above sea level of 59 feet. Within 10 miles contains only modest variations in elevation (3,406 feet). Within 50 miles also contains extreme variations in elevation (10,771 feet).
The area within 2 miles of Sumas is covered by cropland (82%), within 10 miles by cropland (45%) and trees (31%), and within 50 miles by trees (52%) and water (18%).
This report illustrates the typical weather in Sumas, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 2 weather stations near enough to contribute to our estimation of the temperature and dew point in Sumas.
For each station, the records are corrected for the elevation difference between that station and Sumas according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at Sumas is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Sumas and a given station.
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.
The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.
We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.
We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.