This report describes the typical weather at the Paris Orly Airport (Paris, France) 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.
Paris has a mild humid temperate climate with warm summers and no dry season. The area within 25 mi of this station is covered by croplands (74%), built-up areas (18%), and forests (6%).
The month of September is characterized by falling daily high temperatures, with daily highs decreasing from 72°F to 66°F over the course of the month, exceeding 81°F or dropping below 58°F only one day in ten.
Over the course of September, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1:43 hours, implying an average day-over-day decrease of 3.4 minutes.
The shortest day of the month is September 30 with 11:42 hours of daylight; the longest day is September 1 with 13:24 hours of daylight.
The earliest sunrise is at 7:08am on September 1; the latest sunset is at 8:32pm on September 1; the latest sunrise is at 7:49am on September 30; the earliest sunset is at 7:30pm 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 50% (partly cloudy) to 62% (partly cloudy). The trend is for the sky to be becoming cloudier with the median cloud cover increasing by 12% from the start to the end of the month.
On September 1, the clearest day of the month, the sky is clear, mostly clear, or partly cloudy 67% of the time, and overcast or mostly cloudy 30% of the time.
On September 30, the cloudiest day of the month, the sky is overcast, mostly cloudy, or partly cloudy 60% of the time, and clear or mostly clear 37% of the time.
The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around September 30, occurring in 49% of days. Precipitation is least likely around September 1, occurring in 43% of days.
Throughout September, the most common forms of precipitation are moderate rain, thunderstorms, and light rain.
Moderate rain is the most severe precipitation observed during 71% of those days with precipitation. It is most likely around September 30, when it is observed during 36% of all days.
Thunderstorms are the most severe precipitation observed during 14% of those days with precipitation. They are most likely around September 1, when it is observed during 9% of all days.
Light rain is the most severe precipitation observed during 10% of those days with precipitation. It is most likely around September 29, when it is observed during 5% of all days.
Either snow is exceptionally unlikely to fall at this location in September or this station does not reliably report precipitation types.
The relative humidity typically ranges from 49% (comfortable) to 96% (very humid) over the course of a typical September, rarely dropping below 36% (comfortable) and reaching as high as 100% (very humid).
The air is driest around September 1, at which time the relative humidity drops below 56% (mildly humid) three days out of four; it is most humid around September 30, rising above 93% (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 46°F (dry) to 58°F (comfortable) and is rarely below 39°F (dry) or above 64°F (mildy humid).
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 2 mph to 13 mph (light air to moderate breeze), rarely exceeding 20 mph (fresh breeze).
The highest average wind speed of 8 mph (gentle breeze) occurs around September 4, at which time the average daily maximum wind speed is 13 mph (moderate breeze).
The lowest average wind speed of 8 mph (gentle breeze) occurs around September 25, at which time the average daily maximum wind speed is 13 mph (moderate breeze).