Average Weather in Adelphi Maryland, United States
In Adelphi, the summers are hot and humid, the winters are very cold and windy, and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 28°F to 88°F and is rarely below 15°F or above 96°F.
Based on the tourism score, the best times of year to visit Adelphi for warm-weather activities are for the entire month of June and from early August to late September.
The hot season lasts for 3.5 months, from May 30 to September 15, with an average daily high temperature above 79°F. The hottest day of the year is July 21, with an average high of 88°F and low of 69°F.
The cold season lasts for 3.2 months, from November 30 to March 4, with an average daily high temperature below 52°F. The coldest day of the year is January 30, with an average low of 28°F and high of 44°F.
Average High and Low Temperature
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
In Adelphi, 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 Adelphi begins around July 3 and lasts for 4.4 months, ending around November 14. On September 23, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 64% of the time, and overcast or mostly cloudy 36% of the time.
The cloudier part of the year begins around November 14 and lasts for 7.6 months, ending around July 3. On January 5, the cloudiest day of the year, the sky is overcast or mostly cloudy 53% of the time, and clear, mostly clear, or partly cloudy 47% of the time.
Cloud Cover Categories
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Adelphi varies throughout the year.
The wetter season lasts 4.5 months, from April 9 to August 24, with a greater than 30% chance of a given day being a wet day. The chance of a wet day peaks at 39% on July 13.
The drier season lasts 7.5 months, from August 24 to April 9. The smallest chance of a wet day is 21% on October 20.
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 39% on July 13.
Daily Chance of Precipitation
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. Adelphi experiences some seasonal variation in monthly rainfall.
Rain falls throughout the year in Adelphi. The most rain falls during the 31 days centered around May 26, with an average total accumulation of 3.6 inches.
The least rain falls around January 30, with an average total accumulation of 2.0 inches.
Average Monthly Rainfall
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Adelphi experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 4.0 months, from November 24 to March 24, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around February 4, with an average total liquid-equivalent accumulation of 0.6 inches.
The snowless period of the year lasts for 8.0 months, from March 24 to November 24. The least snow falls around July 19, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in Adelphi varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 26 minutes of daylight; the longest day is June 21, with 14 hours, 55 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:41 AM on June 14, and the latest sunrise is 1 hour, 56 minutes later at 7:37 AM on November 3. The earliest sunset is at 4:45 PM on December 7, and the latest sunset is 3 hours, 52 minutes later at 8:37 PM on June 28.
Daylight saving time (DST) is observed in Adelphi 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
Adelphi experiences extreme seasonal variation in the perceived humidity.
The muggier period of the year lasts for 4.1 months, from May 24 to September 28, during which time the comfort level is muggy, oppressive, or miserable at least 16% of the time. The muggiest day of the year is July 29, with muggy conditions 65% of the time.
The least muggy day of the year is February 11, when muggy conditions are essentially unheard of.
Humidity Comfort Levels
The average hourly wind speed in Adelphi experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 6.7 months, from October 19 to May 9, with average wind speeds of more than 8.6 miles per hour. The windiest day of the year is February 26, with an average hourly wind speed of 10.7 miles per hour.
The calmer time of year lasts for 5.3 months, from May 9 to October 19. The calmest day of the year is August 1, with an average hourly wind speed of 6.5 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Adelphi varies throughout the year.
The wind is most often from the north for 2.0 weeks, from March 8 to March 22, with a peak percentage of 31% on March 10. The wind is most often from the west for 1.3 months, from March 22 to May 1; for 4.0 weeks, from June 26 to July 24; and for 4.9 months, from October 12 to March 8, with a peak percentage of 35% on July 6. The wind is most often from the south for 1.8 months, from May 1 to June 26 and for 2.6 months, from July 24 to October 12, with a peak percentage of 35% on August 16.
Adelphi 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 extreme seasonal variation over the course of the year.
The time of year with warmer water lasts for 3.3 months, from June 24 to October 2, with an average temperature above 69°F. The day of the year with the warmest water is August 11, with an average temperature of 77°F.
The time of year with cooler water lasts for 3.6 months, from December 19 to April 6, with an average temperature below 44°F. The day of the year with the coolest water is February 8, with an average temperature of 36°F.
Average Water Temperature
Best Time of Year to Visit
To characterize how pleasant the weather is in Adelphi 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 Adelphi for general outdoor tourist activities are for the entire month of June 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 Adelphi for hot-weather activities is from late June to early September, with a peak score in the third week of July.
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.
The growing season in Adelphi typically lasts for 7.0 months (213 days), from around April 3 to around November 2, rarely starting before March 17 or after April 21, and rarely ending before October 15 or after November 20.
Time Spent in Various Temperature Bands and the Growing Season
Based on growing degree days alone, the first spring blooms in Adelphi should appear around March 19, only rarely appearing before March 3 or after April 5.
Growing Degree Days
The average daily incident shortwave solar energy experiences significant seasonal variation over the course of the year.
The brighter period of the year lasts for 3.8 months, from April 28 to August 23, with an average daily incident shortwave energy per square meter above 5.9 kWh. The brightest day of the year is June 23, with an average of 6.9 kWh.
The darker period of the year lasts for 3.1 months, from November 6 to February 9, with an average daily incident shortwave energy per square meter below 3.0 kWh. The darkest day of the year is December 23, with an average of 2.0 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Adelphi are 39.003 deg latitude, -76.972 deg longitude, and 180 ft elevation.
The topography within 2 miles of Adelphi contains only modest variations in elevation, with a maximum elevation change of 322 feet and an average elevation above sea level of 188 feet. Within 10 miles contains only modest variations in elevation (561 feet). Within 50 miles contains significant variations in elevation (1,890 feet).
The area within 2 miles of Adelphi is covered by artificial surfaces (86%), within 10 miles by artificial surfaces (74%) and trees (21%), and within 50 miles by trees (37%) and cropland (26%).
This report illustrates the typical weather in Adelphi, 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 Adelphi.
For each station, the records are corrected for the elevation difference between that station and Adelphi 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 Adelphi is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Adelphi and a given station.
The stations contributing to this reconstruction are: College Park Airport (76%, 5.0 kilometers, southeast); Ronald Reagan Washington National Airport (15%, 18 kilometers, south); and Montgomery County Airpark (9%, 25 kilometers, northwest).
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.
Time zones for aiports and weather stations are provided by AskGeo.com .