This report describes the historical weather record at the Spirit of St. Louis Airport (St. Louis, Missouri, United States) during the last 12 months. This station has records back to December 1972.
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%)
Daylight saving time (DST) was observed at St. Louis, Missouri during the last 12 months. There were two time changes during the last 12 months:
2013 is not a leap year, so it has 365 days and no February 29th. The first leap year before 2013 was 2012 and the first after will be 2016.
The summer and winter solstices and the spring and fall equinoxes mark the passing of the seasons. They fall on nearly the same day each year, with differences of a day or two depending on the year. In 2013 they occurred on:
|Spring Equinox||Wednesday, 20 March 2013.|
|Summer Solstice||Friday, 21 June 2013.|
|Fall Equinox||Sunday, 22 September 2013.|
|Winter Solstice||Saturday, 21 December 2013.|
The hottest day of the last 12 months was July 16, with a high temperature of 102°F. For reference, on that day the average high temperature is 89°F and the high temperature exceeds 96°F only one day in ten. The hottest month of the last 12 months was August with an average daily high temperature of 86°F.
Relative to the average, the hottest day was January 28. The high temperature that day was 74°F, compared to the average of 41°F, a difference of 33°F. In relative terms the warmest month was December, with an average high temperature of 49°F, compared to an typical value of 44°F.
The longest warm spell was from June 15 to June 29, constituting 15 consecutive days with warmer than average high temperatures. The month of September had the largest fraction of warmer than average days with 73% days with higher than average high temperatures.
The coldest day of the last 12 months was February 1, with a low temperature of 8°F. For reference, on that day the average low temperature is 24°F and the low temperature drops below 10°F only one day in ten. The coldest month of the last 12 months was January with an average daily low temperature of 24°F.
Relative to the average, the coldest day was March 27. The low temperature that day was 19°F, compared to the average of 40°F, a difference of 21°F. In relative terms the coldest month was March, with an average low temperature of 30°F, compared to an typical value of 36°F.
The longest cold spell was from March 19 to March 31, constituting 13 consecutive days with cooler than average low temperatures. The month of March had the largest fraction of cooler than average days with 77% days with lower than average low temperatures.
The clearest month of the last 12 months was September, with 63% of days being more clear than cloudy. The longest spell of clear weather was from August 19 to August 27, constituting 9 consecutive days that were clearer than they were cloudy.
The cloudiest month of the last 12 months was March, with 65% of days being more cloudy than clear. The longest spell of cloudy weather was from February 25 to March 7, constituting 11 consecutive days that were cloudier than they were clear.
This station reports both the quantity of liquid precipitation and categorical observations of precipitation (e.g., moderate rain, or heavy snow). Both are subject to erroneous reports, but the former is particularly prone to false reports, especially ones indicating an excessive quantity of precipitation. Please bear this in mind when reading the extrema reported in this section.
The day with the largest quantity of precipitation was May 3. That day saw 2.328" of liquid (or liquid equivalent) precipitation, compared to a median value of 0.180". The month with the most precipitation was May, with 8.742", compared to a median value of 3.972".
As determined by quantitative measurements, the longest dry spell was from August 14 to September 8, constituting 26 consecutive days with no measured precipitation. The month with the largest fraction of dry days was January, with 81% of days reporting no measured precipitation at all.
The month with the largest fraction of days with at least some measured precipitation was May, with 48% of days reporting some measured precipitation.
This station reports when significant weather events (including precipitation) are visually observed at or near the station. Such events do not always correspond to measured quantities of liquid equivalent precipitation, such as when the event is near by not at the station, or in the case of solid precipitation that does not melt in the collection basin.
The day in the last 12 months with the most precipitation observations was May 3. There were 24 hourly weather reports that day (out of a maximum of 24) in which some form of precipitation was observated at or near the station. The month with the most precipitation observations was March, with 116 hourly present weather reports involving some form of precipitation.
As determined by the present weather reports, the longest dry spell was from July 11 to July 21, constituting 11 consecutive days with no observed precipitation. The month with the largest fraction of days without observed precipitation was July, with 77% of days reporting no observed precipitation at all.
The month with the largest fraction of days with at least some observed precipitation was March, with 55% of days reporting some observed precipitation.
In this section we consider only those weather reports that indicate liquid precipitation. For the purposes of this analysis, we include thunderstorms even though some thunderstorms are not accompanied by liquid precipitation.
The month of the last 12 months with the largest number of those reports was May, with a total of 87 reports. The day with the largest number of those reports was May 3, with a total of 24 reports.
This station reports when snow is observed falling but does not report the quantity of snow that has fallen or the depth of snow on the ground.
In this section we consider hourly weather reports that contain an observation of falling snow. These reports do not necessarily correspond to accumulation.
The first reported snow fall in the last 12 months was on December 20; the last was on December 6. The month of the last 12 months with the largest number of those reports was March, with a total of 57 reports. The day with the largest number of those reports was March 24, with a total of 17 reports.
Humidity is an important factor in determining how weather conditions feel to a person experiencing them. Hot and humid days feel even hotter than hot and dry days because the high level of water content in humid air discourages the evaporation of sweat from a person's skin.
When reading the graph below, keep in mind that the hottest part of the day tends to be the least humid, so the daily low (brown) traces are more relevant for understanding daytime comfort than the daily high (blue) traces, which typically occur during the night. Applying that observation, the least humid month of the last 12 months was September with an average daily low humidity of 41%, and the most humid month was December with an average daily low humidity of 53%.
But it is important to keep in mind that humidity does not tell the whole picture and the dew point is often a better measure of how comfortable a person will find a given set of weather conditions. Please see the next section for continued discussion of this point.
Dew point is the temperature below which water vapor will condense into liquid water. It is therefore also related to the rate of evaporation of liquid water. Since the evaporation of sweat is an important cooling mechanism for the human body, the dew point is an important measurement for understanding how dry, comfortable, or humid a given set of weather conditions will feel.
Generally speaking, dew points below 50°F will feel a bit dry to some people, but comfortable to people accustomed to dry conditions; dew points from 50°F to 68°F are fairly comfortable to most people, and dew points above 68°F are increasingly uncomfortable, becoming oppressive around 77°F.
To take some examples, and basing our categorization on the daily high dew point in the last 12 months, January had 25 dry days, 6 comfortable days, and no humid days; April had 16 dry days, 14 comfortable days, and no humid days; July had no dry days, 12 comfortable days, and 19 humid days; and October had 15 dry days, 12 comfortable days, and 4 humid days.
The highest sustained wind speed was 49 mph, occurring on May 31; the highest daily mean wind speed was 20 mph (December 20); and the highest wind gust speed was 62 mph (May 31).
The windiest month was February, with an average wind speed of 8 mph. The least windy month was August, with an average wind speed of 3 mph.
Visibility is the maximum distance at which a given reference object or light can be clearly discerned. In the United States, visibilities that are greater than or equal to 10 miles are typically reported as 10 miles.
The day of the last 12 months with the lowest average visibility was March 24, with an average visibility of 2.2 mi. The month with the lowest average visibility was December, with an average visibility of 8.8 mi. With an average visibility of 9.6 mi, the month of June had the highest average visibility.
The cloud ceiling is the altitude of the lowest layer of clouds that are at categorized as broken (mostly cloudy) or overcast (cloudy). If no such cloud layer exists then the ceiling is unlimited and no value is reported.
The day of the last 12 months with the lowest average cloud ceiling was September 22, with an average cloud ceiling of 100'. The month with the lowest average cloud ceiling was February, with an average cloud ceiling of 7338'. The month of June has the highest average cloud ceiling, with an average cloud ceiling of 12768'.