Average Weather in Decatur Alabama, United States
In Decatur, the summers are long, hot, and muggy; the winters are short, very cold, and wet; and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 33°F to 89°F and is rarely below 19°F or above 96°F.
Based on the tourism score, the best times of year to visit Decatur for warm-weather activities are from early May to late June and from mid August to mid October.
The hot season lasts for 4.0 months, from May 24 to September 22, with an average daily high temperature above 81°F. The hottest day of the year is July 22, with an average high of 89°F and low of 70°F.
The cool season lasts for 2.9 months, from November 29 to February 25, with an average daily high temperature below 58°F. The coldest day of the year is January 17, with an average low of 33°F and high of 50°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
Bir el Ater, Algeria (5,166 miles away); Kafr Takhārīm, Syria (6,353 miles); and Yangzhong, China (7,872 miles) are the far-away foreign places with temperatures most similar to Decatur (view comparison).
In Decatur, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in Decatur begins around June 7 and lasts for 5.4 months, ending around November 20. On October 2, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 67% of the time, and overcast or mostly cloudy 33% of the time.
The cloudier part of the year begins around November 20 and lasts for 6.6 months, ending around June 7. On January 5, the cloudiest day of the year, the sky is overcast or mostly cloudy 56% of the time, and clear, mostly clear, or partly cloudy 44% 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 Decatur varies throughout the year.
The wetter season lasts 8.2 months, from December 9 to August 16, with a greater than 32% chance of a given day being a wet day. The chance of a wet day peaks at 42% on July 9.
The drier season lasts 3.8 months, from August 16 to December 9. The smallest chance of a wet day is 22% on October 15.
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 42% on July 9.
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. Decatur experiences significant seasonal variation in monthly rainfall.
Rain falls throughout the year in Decatur. The most rain falls during the 31 days centered around December 4, with an average total accumulation of 5.1 inches.
The least rain falls around August 22, with an average total accumulation of 2.8 inches.
Average Monthly Rainfall
The sliding 31-day liquid-equivalent quantity of snowfall in Decatur does not vary significantly over the course of the year, staying within 0.1 inches of 0.1 inches throughout.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in Decatur varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 50 minutes of daylight; the longest day is June 21, with 14 hours, 29 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:34 AM on June 12, and the latest sunrise is 1 hour, 36 minutes later at 7:10 AM on November 3. The earliest sunset is at 4:37 PM on December 5, and the latest sunset is 3 hours, 28 minutes later at 8:04 PM on June 29.
Daylight saving time (DST) is observed in Decatur 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
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.
Decatur experiences extreme seasonal variation in the perceived humidity.
The muggier period of the year lasts for 4.4 months, from May 16 to September 29, during which time the comfort level is muggy, oppressive, or miserable at least 22% of the time. The muggiest day of the year is July 23, with muggy conditions 89% of the time.
The least muggy day of the year is February 5, when muggy conditions are essentially unheard of.
Humidity Comfort Levels
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 Decatur experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 6.7 months, from October 23 to May 15, with average wind speeds of more than 5.8 miles per hour. The windiest day of the year is February 25, with an average hourly wind speed of 7.4 miles per hour.
The calmer time of year lasts for 5.3 months, from May 15 to October 23. The calmest day of the year is July 28, with an average hourly wind speed of 4.2 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Decatur varies throughout the year.
The wind is most often from the north for 1.3 months, from January 17 to February 25 and for 2.4 months, from August 2 to October 15, with a peak percentage of 34% on January 29. The wind is most often from the south for 4.2 months, from February 25 to July 1; for 2.0 days, from July 31 to August 2; and for 3.1 months, from October 15 to January 17, with a peak percentage of 45% on May 4. The wind is most often from the west for 4.3 weeks, from July 1 to July 31, with a peak percentage of 34% on July 14.
Best Time of Year to Visit
To characterize how pleasant the weather is in Decatur 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 Decatur for general outdoor tourist activities are from early May to late June and from mid August to mid October, with a peak score in the third 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 Decatur for hot-weather activities is from mid June to early September, with a peak score in the second week of August.
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 Decatur typically lasts for 7.3 months (225 days), from around March 25 to around November 4, rarely starting before March 3 or after April 13, and rarely ending before October 17 or after November 24.
Time Spent in Various Temperature Bands and 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.
Based on growing degree days alone, the first spring blooms in Decatur should appear around February 16, only rarely appearing before January 28 or after March 8.
Growing Degree Days
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 significant seasonal variation over the course of the year.
The brighter period of the year lasts for 4.8 months, from April 10 to September 3, with an average daily incident shortwave energy per square meter above 5.8 kWh. The brightest day of the year is June 5, with an average of 6.6 kWh.
The darker period of the year lasts for 2.8 months, from November 13 to February 5, with an average daily incident shortwave energy per square meter below 3.3 kWh. The darkest day of the year is December 25, with an average of 2.4 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Decatur are 34.606 deg latitude, -86.983 deg longitude, and 568 ft elevation.
The topography within 2 miles of Decatur is essentially flat, with a maximum elevation change of 66 feet and an average elevation above sea level of 569 feet. Within 10 miles is essentially flat (341 feet). Within 50 miles contains only modest variations in elevation (1,608 feet).
The area within 2 miles of Decatur is covered by artificial surfaces (66%) and water (30%), within 10 miles by cropland (53%) and trees (18%), and within 50 miles by cropland (49%) and trees (44%).
This report illustrates the typical weather in Decatur, 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 4 weather stations near enough to contribute to our estimation of the temperature and dew point in Decatur.
For each station, the records are corrected for the elevation difference between that station and Decatur 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 Decatur is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Decatur and a given station.
The stations contributing to this reconstruction are: Pryor Field (89%, 6 kilometers, northeast); Cullman Regional Airport-Folsom Field (5%, 39 kilometers, south); Muscle Shoals Regional Airport (3.2%, 59 kilometers, west); and Posey Field (2.5%, 68 kilometers, southwest).
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.