September Weather in Grand Rapids Michigan, United States
Daily high temperatures decrease by 11°F, from 77°F to 66°F, rarely falling below 55°F or exceeding 86°F.
Daily low temperatures decrease by 10°F, from 59°F to 48°F, rarely falling below 37°F or exceeding 69°F.
For reference, on July 19, the hottest day of the year, temperatures in Grand Rapids typically range from 63°F to 83°F, while on January 29, the coldest day of the year, they range from 18°F to 30°F.
Average High and Low Temperature in September in Grand Rapids
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 Grand Rapids
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 Grand Rapids experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 34% to 39%.
The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 66% of the time.
For reference, on January 7, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 69%, while on August 7, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 67%.
Cloud Cover Categories in September in Grand Rapids
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 Grand Rapids, the chance of a wet day over the course of September is essentially constant, remaining around 31% throughout.
For reference, the year's highest daily chance of a wet day is 33% on May 24, and its lowest chance is 17% on February 8.
Probability of Precipitation in September in Grand Rapids
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 Grand Rapids is essentially constant, remaining about 3.1 inches throughout, and rarely exceeding 5.7 inches or falling below 1.2 inches.
The highest average 31-day accumulation is 3.3 inches on September 23.
Average Monthly Rainfall in September in Grand Rapids
Over the course of September in Grand Rapids, 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, 23 minutes, implying an average daily decrease of 2 minutes, 53 seconds, and weekly decrease of 20 minutes, 8 seconds.
The shortest day of the month is September 30, with 11 hours, 46 minutes of daylight and the longest day is September 1, with 13 hours, 9 minutes of daylight.
Hours of Daylight and Twilight in September in Grand Rapids
The earliest sunrise of the month in Grand Rapids is 7:07 AM on September 1 and the latest sunrise is 32 minutes later at 7:39 AM on September 30.
The latest sunset is 8:16 PM on September 1 and the earliest sunset is 52 minutes earlier at 7:25 PM on September 30.
Daylight saving time is observed in Grand Rapids during 2021, 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 6:03 AM and sets 15 hours, 22 minutes later, at 9:25 PM, while on December 21, the shortest day of the year, it rises at 8:10 AM and sets 9 hours, 0 minutes later, at 5:11 PM.
Sunrise & Sunset with Twilight in September in Grand Rapids
The figure below presents a compact representation of key lunar data for September 2021. 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 Grand Rapids
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 Grand Rapids is rapidly decreasing during September, falling from 22% to 4% over the course of the month.
For reference, on July 28, the muggiest day of the year, there are muggy conditions 36% of the time, while on November 16, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in September in Grand Rapids
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 Grand Rapids is increasing during September, increasing from 8.6 miles per hour to 10.1 miles per hour over the course of the month.
For reference, on January 12, the windiest day of the year, the daily average wind speed is 12.6 miles per hour, while on August 3, the calmest day of the year, the daily average wind speed is 7.8 miles per hour.
Average Wind Speed in September in Grand Rapids
The hourly average wind direction in Grand Rapids throughout September is predominantly from the south, with a peak proportion of 32% on September 18.
Wind Direction in September in Grand Rapids
Grand Rapids 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 Grand Rapids is decreasing during September, falling by 7°F, from 70°F to 62°F, over the course of the month.
Average Water Temperature in September in Grand Rapids
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 Grand Rapids typically lasts for 5.5 months (167 days), from around April 29 to around October 13, rarely starting before April 11 or after May 18, and rarely ending before September 26 or after October 31.
The month of September in Grand Rapids is more likely than not fully within the growing season, with the chance that a given day is in the growing season decreasing from 100% to 83% over the course of the month.
Time Spent in Various Temperature Bands and the Growing Season in September in Grand Rapids
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 Grand Rapids are increasing during September, increasing by 373°F, from 2,371°F to 2,743°F, over the course of the month.
Growing Degree Days in September in Grand Rapids
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 Grand Rapids is decreasing during September, falling by 1.4 kWh, from 5.5 kWh to 4.1 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in September in Grand Rapids
For the purposes of this report, the geographical coordinates of Grand Rapids are 42.963 deg latitude, -85.668 deg longitude, and 636 ft elevation.
The topography within 2 miles of Grand Rapids contains only modest variations in elevation, with a maximum elevation change of 197 feet and an average elevation above sea level of 666 feet. Within 10 miles also contains only modest variations in elevation (318 feet). Within 50 miles contains only modest variations in elevation (787 feet).
The area within 2 miles of Grand Rapids is covered by artificial surfaces (100%), within 10 miles by artificial surfaces (61%) and cropland (21%), and within 50 miles by cropland (44%) and trees (31%).
This report illustrates the typical weather in Grand Rapids, 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 Grand Rapids.
For each station, the records are corrected for the elevation difference between that station and Grand Rapids 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 Grand Rapids is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Grand Rapids and a given station.
The stations contributing to this reconstruction are: Gerald R. Ford International Airport (KGRR, 66%, 15 kilometers, southeast); West Michigan Regional Airport (KBIV, 15%, 43 kilometers, southwest); Muskegon County Airport (KMKG, 11%, 52 kilometers, northwest); and Fremont Municipal Airport (KFFX, 9%, 59 kilometers, northwest).
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 © 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.