Average Weather in May in Berwyn Pennsylvania, United States
Daily high temperatures increase by 8°F, from 68°F to 76°F, rarely falling below 57°F or exceeding 87°F.
Daily low temperatures increase by 10°F, from 48°F to 57°F, rarely falling below 39°F or exceeding 66°F.
For reference, on July 21, the hottest day of the year, temperatures in Berwyn typically range from 67°F to 85°F, while on January 30, the coldest day of the year, they range from 24°F to 38°F.
Average High and Low Temperature in May
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
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 month of May in Berwyn 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 1, with clear, mostly clear, or partly cloudy conditions 52% of the time.
For reference, on January 5, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 54%, while on September 23, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 64%.
Cloud Cover Categories in May
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. In Berwyn, the chance of a wet day over the course of May is increasing, starting the month at 30% and ending it at 36%.
For reference, the year's highest daily chance of a wet day is 37% on July 29, and its lowest chance is 21% on January 28.
Probability of Precipitation in May
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 Berwyn is essentially constant, remaining about 3.5 inches throughout, and rarely exceeding 6.0 inches or falling below 1.6 inches.
The lowest average 31-day accumulation is 3.4 inches on May 3.
Average Monthly Rainfall in May
Over the course of May in Berwyn, the length of the day is increasing. From the start to the end of the month, the length of the day increases by 54 minutes, implying an average daily increase of 1 minute, 48 seconds, and weekly increase of 12 minutes, 36 seconds.
The shortest day of the month is May 1, with 13 hours, 54 minutes of daylight and the longest day is May 31, with 14 hours, 48 minutes of daylight.
Hours of Daylight and Twilight in May
The latest sunrise of the month in Berwyn is 6:02 AM on May 1 and the earliest sunrise is 27 minutes earlier at 5:35 AM on May 31.
The earliest sunset is 7:56 PM on May 1 and the latest sunset is 27 minutes later at 8:23 PM on May 31.
Daylight saving time is observed in Berwyn during 2019, 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 5:32 AM and sets 15 hours, 1 minute later, at 8:34 PM, while on December 22, the shortest day of the year, it rises at 7:20 AM and sets 9 hours, 19 minutes later, at 4:39 PM.
Sunrise & Sunset with Twilight in May
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 Berwyn is rapidly increasing during May, rising from 1% to 15% over the course of the month.
For reference, on August 2, the muggiest day of the year, there are muggy conditions 55% of the time, while on January 8, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in May
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 Berwyn is decreasing during May, decreasing from 6.4 miles per hour to 5.4 miles per hour over the course of the month.
For reference, on February 26, the windiest day of the year, the daily average wind speed is 7.9 miles per hour, while on August 12, the calmest day of the year, the daily average wind speed is 4.5 miles per hour.
Average Wind Speed in May
Wind Direction in May
Berwyn 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 Berwyn is rapidly increasing during May, rising by 9°F, from 52°F to 61°F, over the course of the month.
Average Water Temperature in May
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 Berwyn typically lasts for 6.7 months (205 days), from around April 8 to around October 30, rarely starting before March 22 or after April 25, and rarely ending before October 12 or after November 16.
The month of May in Berwyn is very likely fully within the growing season, with the chance that a given day is in the growing season gradually increasing from 97% to 100% over the course of the month.
Time Spent in Various Temperature Bands and the Growing Season in May
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.
The average accumulated growing degree days in Berwyn are increasing during May, increasing by 373°F, from 246°F to 619°F, over the course of the month.
Growing Degree Days in May
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 Berwyn is gradually increasing during May, rising by 0.6 kWh, from 6.0 kWh to 6.5 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in May
For the purposes of this report, the geographical coordinates of Berwyn are 40.045 deg latitude, -75.439 deg longitude, and 397 ft elevation.
The topography within 2 miles of Berwyn contains only modest variations in elevation, with a maximum elevation change of 377 feet and an average elevation above sea level of 407 feet. Within 10 miles contains only modest variations in elevation (709 feet). Within 50 miles contains significant variations in elevation (1,631 feet).
The area within 2 miles of Berwyn is covered by artificial surfaces (66%) and trees (34%), within 10 miles by artificial surfaces (53%) and trees (38%), and within 50 miles by cropland (36%) and trees (33%).
This report illustrates the typical weather in Berwyn 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 5 weather stations near enough to contribute to our estimation of the temperature and dew point in Berwyn.
For each station, the records are corrected for the elevation difference between that station and Berwyn 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 Berwyn is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Berwyn and a given station.
The stations contributing to this reconstruction are: Wings Field (41%, 16 kilometers, northeast); Pottstown Limerick Airport (22%, 24 kilometers, northwest); Philadelphia International Airport (17%, 26 kilometers, southeast); Chester County G O Carlson Airport (11%, 37 kilometers, west); and New Castle Airport (9%, 44 kilometers, south).
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.