Climate and Average Weather Year Round in Philadelphia Pennsylvania, United States

In Philadelphia, the summers are warm, humid, and wet; the winters are very cold and snowy; and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 26°F to 87°F and is rarely below 13°F or above 94°F.

Based on the tourism score, the best times of year to visit Philadelphia for warm-weather activities are from early June to early July and from early August to late September.

The hot season lasts for 3.6 months, from May 29 to September 15, with an average daily high temperature above 77°F. The hottest month of the year in Philadelphia is July, with an average high of 86°F and low of 69°F.

The cold season lasts for 3.1 months, from December 1 to March 6, with an average daily high temperature below 49°F. The coldest month of the year in Philadelphia is January, with an average low of 27°F and high of 41°F.

In Philadelphia, the average percentage of the sky covered by clouds experiences mild seasonal variation over the course of the year.

The clearer part of the year in Philadelphia begins around June 24 and lasts for 4.6 months, ending around November 12.

The clearest month of the year in Philadelphia is September, during which on average the sky is clear, mostly clear, or partly cloudy 63% of the time.

The cloudier part of the year begins around November 12 and lasts for 7.4 months, ending around June 24.

The cloudiest month of the year in Philadelphia is January, during which on average the sky is overcast or mostly cloudy 53% of the time.

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

The wetter season lasts 4.9 months, from March 30 to August 26, with a greater than 29% chance of a given day being a wet day. The month with the most wet days in Philadelphia is July, with an average of 11.1 days with at least 0.04 inches of precipitation.

The drier season lasts 7.1 months, from August 26 to March 30. The month with the fewest wet days in Philadelphia is January, with an average of 7.0 days with at least 0.04 inches of precipitation.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. The month with the most days of rain alone in Philadelphia is July, with an average of 11.1 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 37% on July 28.

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. Philadelphia experiences some seasonal variation in monthly rainfall.

Rain falls throughout the year in Philadelphia. The month with the most rain in Philadelphia is July, with an average rainfall of 3.7 inches.

The month with the least rain in Philadelphia is February, with an average rainfall of 2.2 inches.

Snowfall

As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Philadelphia experiences significant seasonal variation in monthly snowfall.

The snowy period of the year lasts for 4.2 months, from November 21 to March 27, with a sliding 31-day snowfall of at least 1.0 inches. The month with the most snow in Philadelphia is January, with an average snowfall of 6.0 inches.

The snowless period of the year lasts for 7.8 months, from March 27 to November 21. The least snow falls around July 31, with an average total accumulation of 0.0 inches.

The length of the day in Philadelphia varies significantly over the course of the year. In 2024, the shortest day is December 21, with 9 hours, 20 minutes of daylight; the longest day is June 20, with 15 hours, 1 minute of daylight.

The earliest sunrise is at 5:31 AM on June 13, and the latest sunrise is 2 hours, 0 minutes later at 7:31 AM on November 2. The earliest sunset is at 4:35 PM on December 7, and the latest sunset is 3 hours, 58 minutes later at 8:33 PM on June 27.

Daylight saving time (DST) is observed in Philadelphia during 2024, starting in the spring on March 10, lasting 7.8 months, and ending in the fall on November 3.

The figure below presents a compact representation of key lunar data for 2024. 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.

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.

Philadelphia experiences extreme seasonal variation in the perceived humidity.

The muggier period of the year lasts for 4.0 months, from May 28 to September 26, during which time the comfort level is muggy, oppressive, or miserable at least 14% of the time. The month with the most muggy days in Philadelphia is July, with 16.6 days that are muggy or worse.

The month with the fewest muggy days in Philadelphia is February, with 0.0 days that are muggy or worse.

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 Philadelphia experiences significant seasonal variation over the course of the year.

The windier part of the year lasts for 6.4 months, from October 27 to May 8, with average wind speeds of more than 7.4 miles per hour. The windiest month of the year in Philadelphia is March, with an average hourly wind speed of 9.0 miles per hour.

The calmer time of year lasts for 5.6 months, from May 8 to October 27. The calmest month of the year in Philadelphia is August, with an average hourly wind speed of 5.7 miles per hour.

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

The wind is most often from the south for 2.3 months, from July 20 to September 28, with a peak percentage of 36% on August 1. The wind is most often from the west for 9.7 months, from September 28 to July 20, with a peak percentage of 45% on January 1.

Philadelphia 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 significant seasonal variation over the course of the year.

The time of year with warmer water lasts for 3.5 months, from June 19 to October 2, with an average temperature above 67°F. The month of the year in Philadelphia with the warmest water is August, with an average temperature of 74°F.

The time of year with cooler water lasts for 3.6 months, from December 21 to April 7, with an average temperature below 46°F. The month of the year in Philadelphia with the coolest water is February, with an average temperature of 39°F.

To characterize how pleasant the weather is in Philadelphia 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 times of year to visit Philadelphia for general outdoor tourist activities are from early June to early July and from early August to late September, with a peak score in the first week of September.

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 Philadelphia for hot-weather activities is from late June to late August, with a peak score in the last week of July.

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.

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 Philadelphia typically lasts for 7.2 months (222 days), from around April 1 to around November 9, rarely starting before March 15 or after April 17, and rarely ending before October 23 or after November 25.

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 Philadelphia should appear around March 29, only rarely appearing before March 13 or after April 13.

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 3.8 months, from April 27 to August 22, with an average daily incident shortwave energy per square meter above 5.9 kWh. The brightest month of the year in Philadelphia is June, with an average of 6.8 kWh.

The darker period of the year lasts for 3.1 months, from November 5 to February 9, with an average daily incident shortwave energy per square meter below 2.8 kWh. The darkest month of the year in Philadelphia is December, with an average of 1.9 kWh.

For the purposes of this report, the geographical coordinates of Philadelphia are 39.952 deg latitude, -75.164 deg longitude, and 39 ft elevation.

The topography within 2 miles of Philadelphia contains only modest variations in elevation, with a maximum elevation change of 105 feet and an average elevation above sea level of 37 feet. Within 10 miles also contains only modest variations in elevation (443 feet). Within 50 miles contains only modest variations in elevation (1,250 feet).

The area within 2 miles of Philadelphia is covered by artificial surfaces (92%), within 10 miles by artificial surfaces (90%), and within 50 miles by trees (41%) and artificial surfaces (27%).