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Average Weather in May in Waterville Washington, United States

Daily low temperatures increase by 8°F, from 39°F to 47°F, rarely falling below 32°F or exceeding 55°F.

For reference, on August 2, the hottest day of the year, temperatures in Waterville typically range from 58°F to 84°F, while on December 30, the coldest day of the year, they range from 18°F to 26°F.

Average High and Low Temperature in May

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 hourly average temperatures for the quarter of the year centered on May. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Average Hourly Temperature in May

Average Hourly Temperature in May in Waterville18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM4 AM8 AM12 PM4 PM8 PM12 AMAprJunvery coldvery coldcoldcoolcoolcomfortable
The average hourly temperature, color coded into bands: 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 shaded overlays indicate night and civil twilight.

Detva, Slovakia (5,366 miles away); Shipka, Bulgaria (5,853 miles); and Yangiobod, Uzbekistan (6,279 miles) are the far-away foreign places with temperatures most similar to Waterville (view comparison).


The month of May in Waterville experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 49% throughout the month.

The clearest day of the month is May 31, with clear, mostly clear, or partly cloudy conditions 52% of the time.

For reference, on January 15, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 67%, while on August 3, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 80%.

Cloud Cover Categories in May

Cloud Cover Categories in May in Waterville1815222911223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%AprJunMay 150%May 150%May 3152%May 3152%May 1150%May 1150%May 2151%May 2151%clearmostly clearpartly cloudymostly cloudyovercast
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.


A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Waterville, the chance of a wet day over the course of May is gradually increasing, starting the month at 12% and ending it at 14%.

For reference, the year's highest daily chance of a wet day is 32% on November 28, and its lowest chance is 5% on July 21.

Probability of Precipitation in May

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).


To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day rainfall during May in Waterville is essentially constant, remaining about 0.7 inches throughout, and rarely exceeding 1.8 inches or falling below 0.1 inches.

The highest average 31-day accumulation is 0.8 inches on May 27.

Average Monthly Rainfall in May

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.


Over the course of May in Waterville, the length of the day is rapidly increasing. From the start to the end of the month, the length of the day increases by 1 hour, 13 minutes, implying an average daily increase of 2 minutes, 25 seconds, and weekly increase of 16 minutes, 57 seconds.

The shortest day of the month is May 1, with 14 hours, 30 minutes of daylight and the longest day is May 31, with 15 hours, 43 minutes of daylight.

Hours of Daylight and Twilight in May

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 latest sunrise of the month in Waterville is 5:42 AM on May 1 and the earliest sunrise is 36 minutes earlier at 5:06 AM on May 31.

The earliest sunset is 8:12 PM on May 1 and the latest sunset is 37 minutes later at 8:49 PM on May 31.

Daylight saving time is observed in Waterville during 2018, but it neither starts nor ends during May, so the entire month is in daylight saving time.

For reference, on June 21, the longest day of the year, the Sun rises at 5:02 AM and sets 15 hours, 60 minutes later, at 9:01 PM, while on December 21, the shortest day of the year, it rises at 7:45 AM and sets 8 hours, 25 minutes later, at 4:11 PM.

Sunrise & Sunset with Twilight in May

The solar day over the course of May. 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.


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 chance that a given day will be muggy in Waterville is essentially constant during May, remaining around 0% throughout.

Humidity Comfort Levels in May

The percentage of time spent at various humidity comfort levels, categorized by dew point: 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 Waterville is essentially constant during May, remaining within 0.1 miles per hour of 6.0 miles per hour throughout.

For reference, on June 8, the windiest day of the year, the daily average wind speed is 6.2 miles per hour, while on January 5, the calmest day of the year, the daily average wind speed is 4.7 miles per hour.

Average Wind Speed in May

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.
The hourly average wind direction in Waterville throughout May is predominantly from the west, with a peak proportion of 59% on May 31.

Wind Direction in May

Wind Direction in May in Waterville1815222911223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%AprJunwestnorthsoutheast
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

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 Waterville typically lasts for 5.3 months (163 days), from around May 1 to around October 11, rarely starting before April 10 or after May 19, and rarely ending before September 21 or after October 31.

During May in Waterville, the chance that a given day is within the growing season is rapidly increasing rising from 50% to 99% over the course of the month.

Time Spent in Various Temperature Bands and the Growing Season in May

Time Spent in Various Temperature Bands and the Growing Season in May in Watervillegrowing season1815222911223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%AprJun50%May 150%May 199%May 3199%May 3174%May 1174%May 1192%May 2192%May 21Apr 1010%Apr 1010%freezingvery coldcoldcoolcomfortablewarm
The percentage of time spent in various temperature bands: 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 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.

The average accumulated growing degree days in Waterville are increasing during May, increasing by 187°F, from 75°F to 262°F, over the course of the month.

Growing Degree Days in May

The average growing degree days accumulated over the course of May, 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 in Waterville is gradually increasing during May, rising by 0.8 kWh, from 6.0 kWh to 6.8 kWh, over the course of the month.

Average Daily Incident Shortwave Solar Energy in May

The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.


For the purposes of this report, the geographical coordinates of Waterville are 47.647 deg latitude, -120.071 deg longitude, and 2,703 ft elevation.

The topography within 2 miles of Waterville contains only modest variations in elevation, with a maximum elevation change of 410 feet and an average elevation above sea level of 2,670 feet. Within 10 miles contains only modest variations in elevation (3,553 feet). Within 50 miles also contains extreme variations in elevation (8,743 feet).

The area within 2 miles of Waterville is covered by cropland (84%) and grassland (13%), within 10 miles by shrubs (43%) and cropland (37%), and within 50 miles by shrubs (47%) and trees (17%).

Data Sources

This report illustrates the typical weather in Waterville year round, 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 Waterville.

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

The stations contributing to this reconstruction are: Pangborn Field (50%, 29 kilometers, south); Ephrata Municipal Airport (33%, 56 kilometers, southeast); and Omak Airport (17%, 100 kilometers, northeast).

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.


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.