Average Weather For St. Louis, Missouri, USA

Location

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 year. 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%).

Temperature

Over the course of a year, the temperature typically varies from 23°F to 89°F and is rarely below 8°F or above 97°F.

Daily High and Low Temperature

The daily average low (blue) and high (red) temperature with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

The warm season lasts from May 26 to September 17 with an average daily high temperature above 79°F. The hottest day of the year is July 25, with an average high of 89°F and low of 69°F.

The cold season lasts from November 29 to February 27 with an average daily high temperature below 50°F. The coldest day of the year is January 18, with an average low of 23°F and high of 40°F.

Fraction of Time Spent in Various Temperature Bands

The average fraction of time spent in various temperature bands: frigid (below 15°F), freezing (15°F to 32°F), cold (32°F to 50°F), cool (50°F to 65°F), comfortable (65°F to 75°F), warm (75°F to 85°F), hot (85°F to 100°F) and sweltering (above 100°F).

Sun

The length of the day varies significantly over the course of the year. The shortest day is December 21 with 9:28 hours of daylight; the longest day is June 20 with 14:52 hours of daylight.

Daily Hours of Daylight and Twilight

The number of hours during which the Sun is visible (black line), with various degrees of daylight, twilight, and night, indicated by the color bands. From bottom (most yellow) to top (most gray): full daylight, solar twilight (Sun is visible but less than 6° from the horizon), civil twilight (Sun is not visible but is less than 6° below the horizon), nautical twilight (Sun is between 6° and 12° below the horizon), astronomical twilight (Sun is between 12° and 18° below the horizon), and full night.

The earliest sunrise is at 5:37am on June 13 and the latest sunset is at 8:32pm on June 28. The latest sunrise is at 7:33am on November 3 and the earliest sunset is at 4:41pm 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.

Daily Sunrise & Sunset with Twilight and Daylight Savings Time

The solar day over the course of the year 2012 . From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (solar, civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight savings time are indicated by the "DST" labels.

Clouds

The median cloud cover ranges from 28% (mostly clear) to 80% (mostly cloudy). The sky is cloudiest on January 17 and clearest on September 14. The clearer part of the year begins around May 20. The cloudier part of the year begins around November 11.

Median Cloud Cover

The median daily cloud cover (black line) with percentile bands (inner band from 40th to 60th percentile, outer band from 25th to 75th percentile).

On September 14, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 66% of the time, and overcast or mostly cloudy 31% of the time.

On January 17, the cloudiest day of the year, the sky is overcast, mostly cloudy, or partly cloudy 61% of the time, and clear or mostly clear 38% of the time.

Cloud Cover Types

The fraction of time spent in each of the five sky cover categories. From top (most blue) to bottom (most gray), the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data.

Precipitation

The probability that precipitation will be observed at this location varies throughout the year. Precipitation is most likely around May 13, occurring in 50% of days. Precipitation is least likely around September 13, occurring in 34% of days.

Probability of Precipitation at Some Point in the Day

The fraction of days in which various types of precipitation are observed. If more than one type of precipitation is reported in a given day, the more severe precipitation is counted. For example, if light rain is observed in the same day as a thunderstorm, that day counts towards the thunderstorm totals. The order of severity is from the top down in this graph, with the most severe at the bottom.

Over the entire year, the most common forms of precipitation are thunderstorms, light rain, moderate rain, and light snow.

Thunderstorms are the most severe precipitation observed during 34% of those days with precipitation. They are most likely around June 11, when it is observed during 29% of all days.

Light rain is the most severe precipitation observed during 26% of those days with precipitation. It is most likely around April 4, when it is observed during 16% of all days.

Moderate rain is the most severe precipitation observed during 15% of those days with precipitation. It is most likely around April 16, when it is observed during 10% of all days.

Light snow is the most severe precipitation observed during 13% of those days with precipitation. It is most likely around January 16, when it is observed during 18% of all days.

Types of Precipitation Throughout the Year

Relative frequency of various types of precipitation over the course of a typical year.

During the warm season, which lasts from May 26 to September 17, there is a 40% 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 (62% of days with precipitation have at worst thunderstorms), light rain (22%), and moderate rain (11%).

During the cold season, which lasts from November 29 to February 27, there is a 45% 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 (34% of days with precipitation have at worst light snow), light rain (22%), moderate rain (16%), and moderate snow (9%).

Warm Season Precipitation

Cold Season Precipitation

Relative frequency of various types of precipitation during the warm and cold seasons respectively.

Snow

The likelihood of snow falling is highest around January 16, occurring in 26% of days. The season in which it is relatively likely for snow to fall spans from November 16 to March 24.

Probability of Snow Fall Being Reported in a Given Day

Probability that snow will be reported at least once in a given day. The season is defined as the period during which the probability is greater than one third the maximum probability.

Either snow rarely accumulates at this location or snow depth measurements are unavailable or unreliable.

Humidity

The relative humidity typically ranges from 40% (comfortable) to 95% (very humid) over the course of the year, rarely dropping below 23% (dry) and reaching as high as 100% (very humid).

The air is driest around April 9, at which time the relative humidity drops below 49% (comfortable) three days out of four; it is most humid around August 22, exceeding 93% (very humid) three days out of four.

Relative Humidity

The average daily high (blue) and low (brown) relative humidity with percentile bands (inner bands from 25th to 75th percentile, outer bands from 10th to 90th percentile).

Dew Point

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 16°F (dry) to 72°F (very muggy) and is rarely below -0°F (dry) or above 78°F (oppressive).

There are two periods in the year that are most comfortable: The first is between April 18 and June 4 and the second is between September 9 and October 19. The air feels neither too dry nor too muggy during these periods.

Dew Point

The daily average low (blue) and high (red) dew point with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

Wind

Over the course of the year typical wind speeds vary from 0 mph to 16 mph (calm to moderate breeze), rarely exceeding 24 mph (fresh breeze).

The highest average wind speed of 9 mph (gentle breeze) occurs around April 2, at which time the average daily maximum wind speed is 16 mph (moderate breeze).

The lowest average wind speed of 5 mph (light breeze) occurs around September 2, at which time the average daily maximum wind speed is 11 mph (gentle breeze).

Wind Speed

The average daily minimum (red), maximum (green), and average (black) wind speed with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
The wind is most often out of the south (13% of the time), west (13% of the time), and south west (11% of the time).

Wind Directions Over the Entire Year

The fraction of time spent with the wind blowing from the various directions over the entire year. Values do not sum to 100% because the wind direction is undefined when the wind speed is zero.

Fraction of Time Spent with Various Wind Directions

The fraction of time spent with the wind blowing from the various directions on a daily basis. Stacked values do not always sum to 100% because the wind direction is undefined when the wind speed is zero.