This report describes the typical weather at the Spirit of St. Louis Airport (St. Louis, Missouri, United States) weather station over the course of an average October. It is based on the historical records from 1987 to 2012. Earlier records are either unavailable or unreliable.
St. Louis, Missouri has a humid continental climate with hot summers and no dry season. The area within 25 mi of this station is covered by forests (46%), croplands (19%), grasslands (18%), built-up areas (14%), and lakes and rivers (4%).
The month of October is characterized by rapidly falling daily high temperatures, with daily highs decreasing from 74°F to 62°F over the course of the month, exceeding 85°F or dropping below 48°F only one day in ten.
Over the course of October, the length of the day is decreasing. From the start to the end of the month, the length of the day decreases by 1:12 hours, implying an average day-over-day decrease of 2.3 minutes.
The shortest day of the month is October 31 with 10:33 hours of daylight; the longest day is October 1 with 11:46 hours of daylight.
The earliest sunrise is at 6:59am on October 1; the latest sunset is at 6:45pm on October 1; the latest sunrise is at 7:29am on October 31; the earliest sunset is at 6:03pm on October 31.
Daylight savings time is observed in 2012 but it neither starts nor ends in October, so the entire month is in daylight time.
The median cloud cover ranges from 33% (mostly clear) to 47% (partly cloudy). The trend is for the sky to be becoming cloudier with the median cloud cover increasing by 14% from the start to the end of the month.
On October 1, the clearest day of the month, the sky is clear, mostly clear, or partly cloudy 64% of the time, and overcast or mostly cloudy 35% of the time.
On October 31, the cloudiest day of the month, the sky is overcast, mostly cloudy, or partly cloudy 51% of the time, and clear or mostly clear 49% of the time.
The average probability that some form of precipitation will be observed in a given day is 36%, with little variation over the course of the month.
Throughout October, the most common forms of precipitation are light rain, thunderstorms, and moderate rain.
Light rain is the most severe precipitation observed during 35% of those days with precipitation. It is most likely around October 23, when it is observed during 13% of all days.
Thunderstorms are the most severe precipitation observed during 29% of those days with precipitation. They are most likely around October 1, when it is observed during 13% of all days.
Moderate rain is the most severe precipitation observed during 19% of those days with precipitation. It is most likely around October 31, when it is observed during 8% of all days.
The likelihood of snow falling is highest around October 31, occurring in 4% of days.
Either snow rarely accumulates at this location in October or snow depth measurements are unavailable or unreliable.
The relative humidity typically ranges from 43% (comfortable) to 95% (very humid) over the course of a typical October, rarely dropping below 25% (dry) and reaching as high as 100% (very humid).
The air is driest around October 5, at which time the relative humidity drops below 50% (comfortable) three days out of four; it is most humid around October 1, 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 October, the dew point typically varies from 33°F (dry) to 56°F (comfortable) and is rarely below 21°F (dry) or above 66°F (muggy).
Over the course of October typical wind speeds vary from 0 mph to 14 mph (calm to moderate breeze), rarely exceeding 21 mph (fresh breeze).
The highest average wind speed of 7 mph (light breeze) occurs around October 31, at which time the average daily maximum wind speed is 14 mph (moderate breeze).
The lowest average wind speed of 6 mph (light breeze) occurs around October 2, at which time the average daily maximum wind speed is 13 mph (moderate breeze).