This report describes the typical weather at the Des Moines International Airport (Des Moines, Iowa, United States) weather station over the course of an average year. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
Des Moines, Iowa has a humid continental climate with hot summers and no dry season. The area within 25 mi of this station is covered by croplands (95%) and built-up areas (3%).
Over the course of a year, the temperature typically varies from 13°F to 86°F and is rarely below -5°F or above 94°F.
The warm season lasts from May 24 to September 17 with an average daily high temperature above 75°F. The hottest day of the year is July 12, with an average high of 86°F and low of 68°F.
The cold season lasts from November 28 to February 27 with an average daily high temperature below 40°F. The coldest day of the year is January 11, with an average low of 13°F and high of 29°F.
The length of the day varies significantly over the course of the year. The shortest day is December 21 with 9:10 hours of daylight; the longest day is June 20 with 15:11 hours of daylight.
The earliest sunrise is at 5:40am on June 15 and the latest sunset is at 8:53pm on June 25. The latest sunrise is at 7:49am on November 3 and the earliest sunset is at 4:44pm on December 9.
Daylight savings time (DST) is observed in this location during 2012, starting in the spring on March 11 and ending in the fall on November 4.
The median cloud cover ranges from 39% (mostly clear) to 83% (mostly cloudy). The sky is cloudiest on December 26 and clearest on September 14. The clearer part of the year begins around June 7. The cloudier part of the year begins around October 29.
On September 14, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 65% of the time, and overcast or mostly cloudy 35% of the time.
On December 26, the cloudiest day of the year, the sky is overcast, mostly cloudy, or partly cloudy 65% of the time, and clear or mostly clear 35% of the time.
The probability that precipitation will be observed at this location varies throughout the year. Precipitation is most likely around January 17, occurring in 53% of days. Precipitation is least likely around September 28, occurring in 34% of days.
Over the entire year, the most common forms of precipitation are thunderstorms, light snow, light rain, and moderate rain.
Thunderstorms are the most severe precipitation observed during 27% of those days with precipitation. They are most likely around June 28, when it is observed during 27% of all days.
Light snow is the most severe precipitation observed during 23% of those days with precipitation. It is most likely around January 14, when it is observed during 32% of all days.
Light rain is the most severe precipitation observed during 23% of those days with precipitation. It is most likely around April 24, when it is observed during 16% of all days.
Moderate rain is the most severe precipitation observed during 11% of those days with precipitation. It is most likely around May 11, when it is observed during 8% of all days.
During the warm season, which lasts from May 24 to September 17, there is a 41% average chance that precipitation will be observed at some point during a given day. When precipitation does occur it is most often in the form of thunderstorms (55% of days with precipitation have at worst thunderstorms), light rain (25%), and moderate rain (14%).
During the cold season, which lasts from November 28 to February 27, there is a 50% average chance that precipitation will be observed at some point during a given day. When precipitation does occur it is most often in the form of light snow (55% of days with precipitation have at worst light snow), moderate snow (16%), light rain (10%), and heavy snow (7%).
The likelihood of snow falling is highest around January 16, occurring in 45% of days. The season in which it is relatively likely for snow to fall spans from November 6 to April 1.
Either snow rarely accumulates at this location or snow depth measurements are unavailable or unreliable.
The relative humidity typically ranges from 42% (comfortable) to 90% (very humid) over the course of the year, rarely dropping below 23% (dry) and reaching as high as 99% (very humid).
The air is driest around April 1, at which time the relative humidity drops below 54% (mildly humid) three days out of four; it is most humid around August 20, exceeding 86% (very humid) three days out of four.
Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.
Over the course of a year, the dew point typically varies from 6°F (dry) to 69°F (muggy) and is rarely below -14°F (dry) or above 76°F (very muggy).
There are two periods in the year that are most comfortable: The first is between May 5 and June 22 and the second is between August 31 and October 5. The air feels neither too dry nor too muggy during these periods.
Over the course of the year typical wind speeds vary from 2 mph to 19 mph (light air to fresh breeze), rarely exceeding 28 mph (strong breeze).
The highest average wind speed of 12 mph (gentle breeze) occurs around April 2, at which time the average daily maximum wind speed is 19 mph (fresh breeze).
The lowest average wind speed of 8 mph (gentle breeze) occurs around August 1, at which time the average daily maximum wind speed is 14 mph (moderate breeze).