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Average Weather in Fort Lewis Washington, United States

In Fort Lewis, the summers are short, warm, dry, and partly cloudy and the winters are very cold, wet, and overcast. Over the course of the year, the temperature typically varies from 35°F to 79°F and is rarely below 24°F or above 90°F.

Based on the tourism score, the best time of year to visit Fort Lewis for warm-weather activities is from mid July to late August.

Climate Summary

coldcoolcomfortablewarmcoolcoldJanFebMarAprMayJunJulAugSepOctNovDec77%77%24%24%clearovercastprecipitation: 8.7 inprecipitation: 8.7 in0.5 in0.5 inmuggy: 0%muggy: 0%0%0%drydrytourism score: 6.5tourism score: 6.50.10.1
Click on each chart for more information.

Temperature

The warm season lasts for 2.8 months, from June 23 to September 16, with an average daily high temperature above 72°F. The hottest day of the year is August 3, with an average high of 79°F and low of 55°F.

The cool season lasts for 3.4 months, from November 13 to February 26, with an average daily high temperature below 52°F. The coldest day of the year is December 20, with an average low of 35°F and high of 45°F.

Average High and Low Temperature

The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

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

Average Hourly Temperature in Fort LewisJanFebMarAprMayJunJulAugSepOctNovDec12 AM4 AM8 AM12 PM4 PM8 PM12 AMvery coldvery coldcoldcoldcoolcomfortablewarm
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
The average hourly temperature, color coded into bands. The shaded overlays indicate night and civil twilight.

Blancos, Spain (5,110 miles away) is the far-away foreign place with temperatures most similar to Fort Lewis (view comparison).

Clouds

In Fort Lewis, the average percentage of the sky covered by clouds experiences extreme seasonal variation over the course of the year.

The clearer part of the year in Fort Lewis begins around June 13 and lasts for 3.8 months, ending around October 7. On August 3, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 77% of the time, and overcast or mostly cloudy 23% of the time.

The cloudier part of the year begins around October 7 and lasts for 8.2 months, ending around June 13. On January 16, the cloudiest day of the year, the sky is overcast or mostly cloudy 76% of the time, and clear, mostly clear, or partly cloudy 24% of the time.

Cloud Cover Categories

Cloud Cover Categories in Fort LewisclearercloudiercloudierJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%Aug 377%Aug 377%Jan 1624%Jan 1624%Jun 1350%Jun 1350%Oct 751%Oct 751%clearmostly cloudyovercastpartly cloudymostly clear
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Fort Lewis varies very significantly throughout the year.

The wetter season lasts 6.8 months, from October 9 to May 2, with a greater than 33% chance of a given day being a wet day. The chance of a wet day peaks at 58% on November 17.

The drier season lasts 5.2 months, from May 2 to October 9. The smallest chance of a wet day is 7% on August 3.

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 56% on November 17.

Daily Chance of Precipitation

Daily Chance of Precipitation in Fort LewiswetwetdryJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Nov 1758%Nov 1758%Aug 37%Aug 37%Jan 150%Jan 150%Oct 933%Oct 933%May 233%May 233%rainmixed
The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

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. Fort Lewis experiences extreme seasonal variation in monthly rainfall.

Rain falls throughout the year in Fort Lewis. The most rain falls during the 31 days centered around November 23, with an average total accumulation of 8.7 inches.

The least rain falls around July 29, with an average total accumulation of 0.5 inches.

Average Monthly Rainfall

Average Monthly Rainfall in Fort LewisJanFebMarAprMayJunJulAugSepOctNovDec0 in5 in10 in15 inNov 238.7 inNov 238.7 inJul 290.5 inJul 290.5 in
The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.

Snowfall

The sliding 31-day liquid-equivalent quantity of snowfall in Fort Lewis does not vary significantly over the course of the year, staying within 0.1 inches of 0.1 inches throughout.

Average Liquid-Equivalent Monthly Snowfall

Average Liquid-Equivalent Monthly Snowfall in Fort LewissnowJanFebMarAprMayJunJulAugSepOctNovDec0 in2 in4 in6 in8 inJan 80.2 inJan 80.2 inJul 70.0 inJul 70.0 inDec 90.1 inDec 90.1 in
The average liquid-equivalent snowfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average rainfall.

Sun

The length of the day in Fort Lewis varies significantly over the course of the year. In 2018, the shortest day is December 21, with 8 hours, 30 minutes of daylight; the longest day is June 21, with 15 hours, 55 minutes of daylight.

Hours of Daylight and Twilight

Hours of Daylight and Twilight in Fort LewisJanFebMarAprMayJunJulAugSepOctNovDec0 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hr12 hr, 7 minMar 2012 hr, 7 minMar 2015 hr, 55 minJun 2115 hr, 55 minJun 2112 hr, 10 minSep 2212 hr, 10 minSep 228 hr, 30 minDec 218 hr, 30 minDec 21nightnightday
The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise is at 5:14 AM on June 16, and the latest sunrise is 2 hours, 42 minutes later at 7:56 AM on January 1. The earliest sunset is at 4:20 PM on December 11, and the latest sunset is 4 hours, 49 minutes later at 9:09 PM on June 25.

Daylight saving time (DST) is observed in Fort Lewis during 2018, starting in the spring on March 11, lasting 7.8 months, and ending in the fall on November 4.

Sunrise & Sunset with Twilight and Daylight Saving Time

Sunrise & Sunset with Twilight and Daylight Saving Time in Fort LewisJanFebMarAprMayJunJulAugSepOctNovDec12 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMJun 165:14 AMJun 165:14 AM9:09 PMJun 259:09 PMJun 25Dec 114:20 PMDec 114:20 PM7:56 AMJan 17:56 AMJan 1Mar 11DSTMar 11DSTDSTNov 4DSTNov 4daynightnightnightnightSolarMidnightSolarMidnightSolarNoonSunriseSunset
The solar day over the course of the year 2018. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight saving time are indicated by the 'DST' labels.

Humidity

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 Fort Lewis, 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, remaining a virtually constant 0% throughout.

Humidity Comfort Levels

Humidity Comfort Levels in Fort LewisJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Jan 280%Jan 280%Sep 130%Sep 130%drydrycomfortablecomfortablehumidhumid
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
The percentage of time spent at various humidity comfort levels, categorized by dew point.

Wind

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 Fort Lewis experiences mild seasonal variation over the course of the year.

The windier part of the year lasts for 6.2 months, from October 16 to April 23, with average wind speeds of more than 4.2 miles per hour. The windiest day of the year is November 30, with an average hourly wind speed of 5.2 miles per hour.

The calmer time of year lasts for 5.8 months, from April 23 to October 16. The calmest day of the year is August 2, with an average hourly wind speed of 3.2 miles per hour.

Average Wind Speed

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The predominant average hourly wind direction in Fort Lewis varies throughout the year.

The wind is most often from the west for 4.5 months, from April 29 to September 15, with a peak percentage of 49% on June 22. The wind is most often from the south for 7.5 months, from September 15 to April 29, with a peak percentage of 55% on January 1.

Wind Direction

Wind Direction in Fort LewisSWSJanFebMarAprMayJunJulAugSepOctNovDec0%100%20%80%40%60%60%40%80%20%100%0%westsoutheastnorth
northeastsouthwest
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions, excluding hours in which the mean wind speed is less than 1.0 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Water Temperature

Fort Lewis 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 3.1 months, from June 24 to September 29, with an average temperature above 55°F. The day of the year with the warmest water is August 23, with an average temperature of 57°F.

The time of year with cooler water lasts for 4.0 months, from December 11 to April 12, with an average temperature below 49°F. The day of the year with the coolest water is February 11, with an average temperature of 47°F.

Average Water Temperature

The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.

Best Time of Year to Visit

To characterize how pleasant the weather is in Fort Lewis 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 Fort Lewis for general outdoor tourist activities is from mid July to late August, with a peak score in the first week of August.

Tourism Score

Tourism Score in Fort LewisJanFebMarAprMayJunJulAugSepOctNovDec02468106.56.50.10.1precipitationprecipitationcloudscloudstemperaturetemperaturetourism score
The tourism score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

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 Fort Lewis for hot-weather activities is from mid July to mid August, with a peak score in the first week of August.

Beach/Pool Score

Beach/Pool Score in Fort LewisJanFebMarAprMayJunJulAugSepOctNovDec02468101.91.90.00.0 precipitationprecipitationcloudscloudstemperaturetemperaturebeach/pool score
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

Methodology

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.

Growing Season

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 Fort Lewis typically lasts for 6.3 months (193 days), from around April 18 to around October 28, rarely starting before March 30 or after May 10, and rarely ending before October 9 or after November 21.

Time Spent in Various Temperature Bands and the Growing Season

Time Spent in Various Temperature Bands and the Growing Season in Fort Lewisgrowing seasonJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%50%Apr 1850%Apr 1850%Oct 2850%Oct 2890%May 1090%May 1090%Oct 990%Oct 910%Mar 3010%Mar 3010%Nov 2110%Nov 210%Dec 280%Dec 28Jul 29100%Jul 29100%freezingvery coldcoldcoolcomfortable
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
The percentage of time spent in various temperature bands. The black line is the percentage chance that a given day is within the growing season.

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 Fort Lewis should appear around April 16, only rarely appearing before March 31 or after May 6.

Growing Degree Days

The average growing degree days accumulated over the course of the year, with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

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 3.1 months, from May 19 to August 24, with an average daily incident shortwave energy per square meter above 5.7 kWh. The brightest day of the year is July 21, with an average of 6.9 kWh.

The darker period of the year lasts for 3.8 months, from October 25 to February 20, with an average daily incident shortwave energy per square meter below 2.1 kWh. The darkest day of the year is December 26, with an average of 0.9 kWh.

Average Daily Incident Shortwave Solar Energy

Average Daily Incident Shortwave Solar Energy in Fort LewisbrightdarkdarkJanFebMarAprMayJunJulAugSepOctNovDec0 kWh1 kWh2 kWh3 kWh4 kWh5 kWh6 kWh7 kWh8 kWh9 kWhJul 216.9 kWhJul 216.9 kWhDec 260.9 kWhDec 260.9 kWhMay 195.7 kWhMay 195.7 kWhOct 252.1 kWhOct 252.1 kWhFeb 202.1 kWhFeb 202.1 kWh
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Topography

For the purposes of this report, the geographical coordinates of Fort Lewis are 47.108 deg latitude, -122.577 deg longitude, and 279 ft elevation.

The topography within 2 miles of Fort Lewis contains only modest variations in elevation, with a maximum elevation change of 217 feet and an average elevation above sea level of 276 feet. Within 10 miles contains only modest variations in elevation (518 feet). Within 50 miles contains significant variations in elevation (14,383 feet).

The area within 2 miles of Fort Lewis is covered by artificial surfaces (69%), water (16%), and trees (15%), within 10 miles by artificial surfaces (36%) and trees (36%), and within 50 miles by trees (53%) and shrubs (17%).

Data Sources

This report illustrates the typical weather in Fort Lewis, 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 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Fort Lewis.

For each station, the records are corrected for the elevation difference between that station and Fort Lewis 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 Fort Lewis is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Fort Lewis and a given station.

The stations contributing to this reconstruction are: Madigan Hospital Heliport (83%, 2.8 kilometers, south); McChord Field Airport (Joint Base Lewis-McChord) (16%, 9 kilometers, northeast); and Sanderson Field (1.3%, 45 kilometers, west).

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , 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.

Disclaimer

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.