Summer Weather in Chester Pennsylvania, United States

Daily high temperatures increase by 4°F, from 78°F to 82°F, rarely falling below 67°F or exceeding 94°F. The highest daily average high temperature is 87°F on July 21.

Daily low temperatures increase by 6°F, from 60°F to 66°F, rarely falling below 52°F or exceeding 76°F. The highest daily average low temperature is 70°F on July 21.

For reference, on July 21, the hottest day of the year, temperatures in Chester typically range from 70°F to 87°F, while on January 30, the coldest day of the year, they range from 26°F to 40°F.

The figure below shows you a compact characterization of the hourly average summer temperatures. 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.

Tbilisi, Georgia (5,677 miles away) is the far-away foreign place with temperatures most similar to Chester (view comparison).

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The summer in Chester experiences rapidly decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 49% to 36%.

The clearest day of the summer is August 29, with clear, mostly clear, or partly cloudy conditions 65% of the time.

For reference, on January 5, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 53%, while on September 23, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 65%.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Chester, the chance of a wet day over the course of the summer is rapidly decreasing, starting the season at 35% and ending it at 29%.

For reference, the year's highest daily chance of a wet day is 38% on July 29, and its lowest chance is 22% on October 20.

Rainfall

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

The average sliding 31-day rainfall during the summer in Chester is essentially constant, remaining about 3.5 inches throughout, and rarely exceeding 6.5 inches or falling below 1.4 inches.

Over the course of the summer in Chester, the length of the day is rapidly decreasing. From the start to the end of the season, the length of the day decreases by 1 hour, 43 minutes, implying an average daily decrease of 1 minute, 8 seconds, and weekly decrease of 7 minutes, 56 seconds.

The shortest day of the summer is August 31, with 13 hours, 6 minutes of daylight and the longest day is June 21, with 15 hours, 0 minutes of daylight.

The earliest sunrise of the summer in Chester is 5:32 AM on June 14 and the latest sunrise is 56 minutes later at 6:28 AM on August 31.

The latest sunset is 8:33 PM on June 27 and the earliest sunset is 1 hour, 0 minutes earlier at 7:34 PM on August 31.

Daylight saving time is observed in Chester during 2026, but it neither starts nor ends during the summer, so the entire season is in daylight saving time.

For reference, on June 21, the longest day of the year, the Sun rises at 5:33 AM and sets 15 hours, 0 minutes later, at 8:33 PM, while on December 21, the shortest day of the year, it rises at 7:19 AM and sets 9 hours, 21 minutes later, at 4:39 PM.

The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation.

The figure below presents a compact representation of key lunar data for the summer of 2026. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.

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 Chester is rapidly increasing during the summer, rising from 20% to 39% over the course of the season.

The highest chance of a muggy day during the summer is 60% on July 29.

For reference, on July 29, the muggiest day of the year, there are muggy conditions 60% of the time, while on January 24, the least muggy day of the year, there are muggy conditions 0% of the time.

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 Chester is gradually decreasing during the summer, decreasing from 6.5 miles per hour to 5.7 miles per hour over the course of the season.

For reference, on February 26, the windiest day of the year, the daily average wind speed is 9.2 miles per hour, while on August 12, the calmest day of the year, the daily average wind speed is 5.4 miles per hour.

The lowest daily average wind speed during the summer is 5.4 miles per hour on August 13.

The wind direction in Chester during the summer is predominantly out of the west from June 1 to June 7 and from June 26 to July 21 and the south from June 7 to June 26 and from July 21 to August 31.

Chester 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 surface water temperature in Chester is very rapidly increasing during the summer, rising by 12°F, from 61°F to 73°F, over the course of the season.

The highest average surface water temperature during the summer is 74°F on August 9.

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 Chester typically lasts for 7.3 months (225 days), from around April 1 to around November 11, rarely starting before March 16 or after April 16, and rarely ending before October 25 or after November 30.

The summer in Chester is reliably fully 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 Chester are very rapidly increasing during the summer, increasing by 2,277°F, from 729°F to 3,006°F, over the course of the season.

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 Chester is gradually decreasing during the summer, falling by 0.9 kWh, from 6.6 kWh to 5.7 kWh, over the course of the season.

The highest average daily incident shortwave solar energy during the summer is 6.9 kWh on June 29.

For the purposes of this report, the geographical coordinates of Chester are 39.850 deg latitude, -75.357 deg longitude, and 13 ft elevation.

The topography within 2 miles of Chester contains only modest variations in elevation, with a maximum elevation change of 108 feet and an average elevation above sea level of 27 feet. Within 10 miles also contains only modest variations in elevation (482 feet). Within 50 miles contains only modest variations in elevation (1,243 feet).

The area within 2 miles of Chester is covered by artificial surfaces (66%) and water (31%), within 10 miles by artificial surfaces (60%) and trees (16%), and within 50 miles by trees (36%) and cropland (30%).