September Weather in Indianapolis Indiana, United States
Daily high temperatures decrease by 10°F, from 82°F to 72°F, rarely falling below 61°F or exceeding 89°F.
Daily low temperatures decrease by 11°F, from 63°F to 52°F, rarely falling below 41°F or exceeding 71°F.
For reference, on July 19, the hottest day of the year, temperatures in Indianapolis typically range from 68°F to 85°F, while on January 29, the coldest day of the year, they range from 22°F to 36°F.
Average High and Low Temperature in September in Indianapolis
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on September. 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 September in Indianapolis
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 September in Indianapolis experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 33% throughout the month.
The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 69% of the time.
For reference, on December 28, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 59%, while on August 23, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 70%.
Cloud Cover Categories in September in Indianapolis
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 Indianapolis, the chance of a wet day over the course of September is decreasing, starting the month at 29% and ending it at 24%.
For reference, the year's highest daily chance of a wet day is 42% on June 26, and its lowest chance is 20% on January 29.
Probability of Precipitation in September in Indianapolis
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 September in Indianapolis is essentially constant, remaining about 2.9 inches throughout, and rarely exceeding 5.6 inches or falling below 0.8 inches.
Average Monthly Rainfall in September in Indianapolis
Over the course of September in Indianapolis, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1 hour, 14 minutes, implying an average daily decrease of 2 minutes, 34 seconds, and weekly decrease of 17 minutes, 58 seconds.
The shortest day of the month is September 30, with 11 hours, 49 minutes of daylight and the longest day is September 1, with 13 hours, 4 minutes of daylight.
Hours of Daylight and Twilight in September in Indianapolis
The earliest sunrise of the month in Indianapolis is 7:12 AM on September 1 and the latest sunrise is 27 minutes later at 7:39 AM on September 30.
The latest sunset is 8:16 PM on September 1 and the earliest sunset is 47 minutes earlier at 7:28 PM on September 30.
Daylight saving time is observed in Indianapolis during 2023, but it neither starts nor ends during September, so the entire month is in daylight saving time.
For reference, on June 21, the longest day of the year, the Sun rises at 6:16 AM and sets 15 hours, 0 minutes later, at 9:16 PM, while on December 22, the shortest day of the year, it rises at 8:02 AM and sets 9 hours, 21 minutes later, at 5:23 PM.
Sunrise & Sunset with Twilight in September in Indianapolis
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.
Solar Elevation and Azimuth in September in Indianapolis
The figure below presents a compact representation of key lunar data for September 2023. 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.
Moon Rise, Set & Phases in September in Indianapolis
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 Indianapolis is very rapidly decreasing during September, falling from 36% to 7% over the course of the month.
For reference, on July 22, the muggiest day of the year, there are muggy conditions 56% of the time, while on December 13, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in September in Indianapolis
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 Indianapolis is increasing during September, increasing from 7.1 miles per hour to 8.4 miles per hour over the course of the month.
For reference, on April 1, the windiest day of the year, the daily average wind speed is 11.4 miles per hour, while on July 31, the calmest day of the year, the daily average wind speed is 6.5 miles per hour.
Average Wind Speed in September in Indianapolis
The hourly average wind direction in Indianapolis throughout September is predominantly from the south, with a peak proportion of 34% on September 24.
Wind Direction in September in Indianapolis
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 Indianapolis typically lasts for 6.5 months (200 days), from around April 8 to around October 26, rarely starting before March 23 or after April 25, and rarely ending before October 4 or after November 15.
The month of September in Indianapolis is very likely fully within the growing season, with the chance that a given day is in the growing season gradually decreasing from 100% to 93% over the course of the month.
Time Spent in Various Temperature Bands and the Growing Season in September in Indianapolis
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 Indianapolis are rapidly increasing during September, increasing by 490°F, from 2,948°F to 3,438°F, over the course of the month.
Growing Degree Days in September in Indianapolis
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 Indianapolis is decreasing during September, falling by 1.2 kWh, from 5.8 kWh to 4.5 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in September in Indianapolis
For the purposes of this report, the geographical coordinates of Indianapolis are 39.768 deg latitude, -86.158 deg longitude, and 712 ft elevation.
The topography within 2 miles of Indianapolis is essentially flat, with a maximum elevation change of 89 feet and an average elevation above sea level of 711 feet. Within 10 miles is essentially flat (564 feet). Within 50 miles contains significant variations in elevation (840 feet).
The area within 2 miles of Indianapolis is covered by artificial surfaces (100%), within 10 miles by artificial surfaces (87%), and within 50 miles by cropland (74%) and trees (17%).
This report illustrates the typical weather in Indianapolis, 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 Indianapolis.
For each station, the records are corrected for the elevation difference between that station and Indianapolis 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 Indianapolis is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Indianapolis and a given station.
The stations contributing to this reconstruction are:
To get a sense of how much these sources agree with each other, you can view a comparison of Indianapolis and the stations that contribute to our estimates of its temperature history and climate. Please note that each source's contribution is adjusted for elevation and the relative change present in the MERRA-2 data.
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , 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 airports and weather stations are provided by AskGeo.com .
Maps are © OpenStreetMap contributors.
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.
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