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 March. 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 March is characterized by rapidly rising daily high temperatures, with daily highs increasing from 51°F to 63°F over the course of the month, exceeding 79°F or dropping below 35°F only one day in ten.
Over the course of March, the length of the day is increasing. From the start to the end of the month, the length of the day increases by 1:15 hours, implying an average day-over-day increase of 2.4 minutes.
The shortest day of the month is March 1 with 11:22 hours of daylight; the longest day is March 31 with 12:37 hours of daylight.
The earliest sunrise is at 6:21am on March 10; the latest sunset is at 7:25pm on March 31; the latest sunrise is at 7:20am on March 11; the earliest sunset is at 5:57pm on March 1.
Daylight savings time (DST) starts at 3:00am on March 11, 2012, shifting sunrise and sunset to an hour later.
The median cloud cover ranges from 59% (partly cloudy) to 71% (partly cloudy). The trend is for the sky to be clearing with the median cloud cover decreasing by 11% from the start to the end of the month.
On March 28, the clearest day of the month, the sky is clear, mostly clear, or partly cloudy 53% of the time, and overcast or mostly cloudy 47% of the time.
On March 2, the cloudiest day of the month, the sky is overcast, mostly cloudy, or partly cloudy 59% of the time, and clear or mostly clear 41% of the time.
The average probability that some form of precipitation will be observed in a given day is 46%, with little variation over the course of the month.
Throughout March, the most common forms of precipitation are light rain, thunderstorms, moderate rain, and light snow.
Light rain is the most severe precipitation observed during 31% of those days with precipitation. It is most likely around March 30, when it is observed during 16% of all days.
Thunderstorms are the most severe precipitation observed during 21% of those days with precipitation. They are most likely around March 31, when it is observed during 14% of all days.
Moderate rain is the most severe precipitation observed during 17% of those days with precipitation. It is most likely around March 31, when it is observed during 9% of all days.
Light snow is the most severe precipitation observed during 16% of those days with precipitation. It is most likely around March 1, when it is observed during 11% of all days.
The likelihood of snow falling is highest around March 1, occurring in 15% of days.
Accumulation at this location in March is extremely unlikely. The chances of there being snow on the ground are highest around March 1, occurring 4% of the time.
The snow is typically at its deepest on March 6, with a median depth of 4.1"; the depth exceeds 4.3" only one year out of ten.
The relative humidity typically ranges from 40% (comfortable) to 88% (very humid) over the course of a typical March, rarely dropping below 23% (dry) and reaching as high as 100% (very humid).
The air is driest around March 31, at which time the relative humidity drops below 49% (comfortable) three days out of four; it is most humid around March 24, rising above 83% (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 March, the dew point typically varies from 23°F (dry) to 44°F (dry) and is rarely below 10°F (dry) or above 59°F (comfortable).
Over the course of March typical wind speeds vary from 0 mph to 16 mph (calm to moderate breeze), rarely exceeding 23 mph (fresh breeze).
The highest average wind speed of 9 mph (gentle breeze) occurs around March 29, at which time the average daily maximum wind speed is 16 mph (moderate breeze).
The lowest average wind speed of 8 mph (gentle breeze) occurs around March 22, at which time the average daily maximum wind speed is 16 mph (moderate breeze).