Climate and Average Weather Year Round in Iowa United StatesIn Iowa, the summers are long, hot, and oppressive; the winters are short and cold; and it is wet and partly cloudy year round. Over the course of the year, the temperature typically varies from 44°F to 91°F and is rarely below 30°F or above 96°F. Based on the tourism score, the best times of year to visit Iowa for warm-weather activities are from early April to late May and from late September to late October. Average Temperature in IowaThe hot season lasts for 4.2 months, from May 20 to September 26, with an average daily high temperature above 85°F. The hottest month of the year in Iowa is July, with an average high of 90°F and low of 75°F. The cool season lasts for 2.9 months, from November 30 to February 24, with an average daily high temperature below 67°F. The coldest month of the year in Iowa is January, with an average low of 44°F and high of 61°F.
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. El Hamma, Tunisia (5,741 miles away); Fuzhou, China (8,007 miles); and Roxby Downs, Australia (9,498 miles) are the far-away foreign places with temperatures most similar to Iowa (view comparison). CloudsIn Iowa, 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 Iowa begins around September 14 and lasts for 2.7 months, ending around December 5. The clearest month of the year in Iowa is October, during which on average the sky is clear, mostly clear, or partly cloudy 67% of the time. The cloudier part of the year begins around December 5 and lasts for 9.3 months, ending around September 14. The cloudiest month of the year in Iowa is July, during which on average the sky is overcast or mostly cloudy 50% of the time.
PrecipitationA wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Iowa varies throughout the year. The wetter season lasts 3.3 months, from May 30 to September 9, with a greater than 38% chance of a given day being a wet day. The month with the most wet days in Iowa is July, with an average of 15.0 days with at least 0.04 inches of precipitation. The drier season lasts 8.7 months, from September 9 to May 30. The month with the fewest wet days in Iowa is October, with an average of 7.9 days with at least 0.04 inches of precipitation. Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. The month with the most days of rain alone in Iowa is July, with an average of 15.0 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 51% on June 29.
RainfallTo 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. Iowa experiences some seasonal variation in monthly rainfall. Rain falls throughout the year in Iowa. The month with the most rain in Iowa is June, with an average rainfall of 5.4 inches. The month with the least rain in Iowa is March, with an average rainfall of 3.8 inches.
SunThe length of the day in Iowa varies significantly over the course of the year. In 2024, the shortest day is December 21, with 10 hours, 12 minutes of daylight; the longest day is June 20, with 14 hours, 6 minutes of daylight.
The earliest sunrise is at 6:09 AM on June 10, and the latest sunrise is 1 hour, 18 minutes later at 7:27 AM on November 2. The earliest sunset is at 5:11 PM on December 1, and the latest sunset is 3 hours, 7 minutes later at 8:17 PM on June 30. Daylight saving time (DST) is observed in Iowa during 2024, starting in the spring on March 10, lasting 7.8 months, and ending in the fall on November 3. 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. MoonThe figure below presents a compact representation of key lunar data for 2024. 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. HumidityWe 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. Iowa experiences extreme seasonal variation in the perceived humidity. The muggier period of the year lasts for 6.5 months, from April 8 to October 25, during which time the comfort level is muggy, oppressive, or miserable at least 29% of the time. The month with the most muggy days in Iowa is July, with 30.5 days that are muggy or worse. The month with the fewest muggy days in Iowa is January, with 2.1 days that are muggy or worse.
WindThis 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 Iowa experiences significant seasonal variation over the course of the year. The windier part of the year lasts for 7.8 months, from October 6 to May 31, with average wind speeds of more than 7.5 miles per hour. The windiest month of the year in Iowa is March, with an average hourly wind speed of 9.1 miles per hour. The calmer time of year lasts for 4.2 months, from May 31 to October 6. The calmest month of the year in Iowa is August, with an average hourly wind speed of 5.9 miles per hour.
The predominant average hourly wind direction in Iowa varies throughout the year. The wind is most often from the south for 6.7 months, from February 12 to September 4 and for 3.7 weeks, from November 7 to December 3, with a peak percentage of 64% on June 7. The wind is most often from the east for 2.1 months, from September 4 to November 7, with a peak percentage of 37% on September 19. The wind is most often from the north for 2.3 months, from December 3 to February 12, with a peak percentage of 37% on January 1. Water TemperatureIowa 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 significant seasonal variation over the course of the year. The time of year with warmer water lasts for 4.0 months, from May 30 to September 28, with an average temperature above 81°F. The month of the year in Iowa with the warmest water is August, with an average temperature of 86°F. The time of year with cooler water lasts for 3.3 months, from December 9 to March 17, with an average temperature below 65°F. The month of the year in Iowa with the coolest water is January, with an average temperature of 60°F.
Best Time of Year to VisitTo characterize how pleasant the weather is in Iowa 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 Iowa for general outdoor tourist activities are from early April to late May and from late September to late October, with a peak score in the last week of April. Tourism Score in IowaThe beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best times of year to visit Iowa for hot-weather activities are from early May to late June and from late August to late September, with a peak score in the first week of June. Beach/Pool Score in IowaMethodologyFor 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. Growing SeasonDefinitions 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 Iowa typically lasts for 9.7 months (296 days), from around February 14 to around December 6, rarely starting before January 9 or after March 15, and rarely ending before November 8 or after January 2. 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 Iowa should appear around January 18, only rarely appearing before January 11 or after February 1. Solar EnergyThis 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 3.0 months, from March 31 to July 1, with an average daily incident shortwave energy per square meter above 5.8 kWh. The brightest month of the year in Iowa is May, with an average of 6.5 kWh. The darker period of the year lasts for 2.5 months, from November 16 to February 1, with an average daily incident shortwave energy per square meter below 3.7 kWh. The darkest month of the year in Iowa is December, with an average of 3.0 kWh.
TopographyFor the purposes of this report, the geographical coordinates of Iowa are 30.237 deg latitude, -93.014 deg longitude, and 20 ft elevation. The topography within 2 miles of Iowa is essentially flat, with a maximum elevation change of 20 feet and an average elevation above sea level of 19 feet. Within 10 miles is essentially flat (108 feet). Within 50 miles also contains only modest variations in elevation (249 feet). The area within 2 miles of Iowa is covered by cropland (91%), within 10 miles by cropland (75%) and herbaceous vegetation (21%), and within 50 miles by herbaceous vegetation (36%) and cropland (30%). Data SourcesThis report illustrates the typical weather in Iowa, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016. Temperature and Dew PointThere are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Iowa. For each station, the records are corrected for the elevation difference between that station and Iowa 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 Iowa is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Iowa 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 Iowa 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. Other DataAll 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. DisclaimerThe 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. Please review our full terms contained on our Terms of Service page. |