This report describes the typical weather at the Dane County Regional Airport (Madison, Wisconsin, United States) weather station over the course of an average September. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
Madison, Wisconsin has a humid continental climate with hot summers and no dry season. The area within 25 mi of this station is covered by grasslands (49%), croplands (45%), and lakes and rivers (3%).
The month of September is characterized by rapidly falling daily high temperatures, with daily highs decreasing from 78Â°F to 65Â°F over the course of the month, exceeding 86Â°F or dropping below 54Â°F only one day in ten.
Over the course of September, the length of the day is decreasing. From the start to the end of the month, the length of the day decreases by 1:24 hours, implying an average day-over-day decrease of 2.8 minutes.
The shortest day of the month is September 30 with 11:45 hours of daylight; the longest day is September 1 with 13:09 hours of daylight.
The earliest sunrise is at 6:22am on September 1; the latest sunset is at 7:31pm on September 1; the latest sunrise is at 6:54am on September 30; the earliest sunset is at 6:39pm on September 30.
Daylight savings time is observed in 2012 but it neither starts nor ends in September, so the entire month is in daylight time.
The median cloud cover ranges from 45% (partly cloudy) to 51% (partly cloudy). The trend is for the sky to be becoming cloudier with the median cloud cover increasing by 6% from the start to the end of the month.
On September 15, a representative day, the sky is clear or mostly clear 47% of the time, partly cloudy 14% of the time, and mostly cloudy or overcast 39% of the time.
The average probability that some form of precipitation will be observed in a given day is 42%, with little variation over the course of the month.
Throughout September, the most common forms of precipitation are light rain, thunderstorms, and moderate rain.
Light rain is the most severe precipitation observed during 36% of those days with precipitation. It is most likely around September 30, when it is observed during 16% of all days.
Thunderstorms are the most severe precipitation observed during 28% of those days with precipitation. They are most likely around September 1, when it is observed during 15% of all days.
Moderate rain is the most severe precipitation observed during 26% of those days with precipitation. It is most likely around September 18, when it is observed during 11% of all days.
The likelihood of snow falling is highest around September 30, occurring in 2% of days.
Either snow rarely accumulates at this location in September or snow depth measurements are unavailable or unreliable.
The relative humidity typically ranges from 50% (comfortable) to 95% (very humid) over the course of a typical September, rarely dropping below 33% (comfortable) and reaching as high as 100% (very humid).
The air is driest around September 30, at which time the relative humidity drops below 58% (mildly humid) three days out of four; it is most humid around September 6, rising above 92% (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 typical September, the dew point typically varies from 40Â°F (dry) to 63Â°F (mildy humid) and is rarely below 29Â°F (dry) or above 70Â°F (muggy).
The time of the month between September 1 and September 30 is the most comfortable, with dew points that are neither too dry nor too muggy.
Over the course of September typical wind speeds vary from 0 mph to 15 mph (calm to moderate breeze), rarely exceeding 20 mph (fresh breeze).
The highest average wind speed of 8 mph (gentle breeze) occurs around September 29, at which time the average daily maximum wind speed is 15 mph (moderate breeze).
The lowest average wind speed of 7 mph (light breeze) occurs around September 1, at which time the average daily maximum wind speed is 13 mph (moderate breeze).