Better Know a City Climatology: St. Louis, MO

In this series we will explore the meteorological characteristics of a particular city in the United States. Using extensive weather data and analytics, we will explore what makes a city unique in its climatology. For each city, we will examine its temperature and precipitation distributions, analyze a significant weather event for the area, and maybe even provide some other interesting tidbits along the way.

For the inaugural piece, we will explore the gateway to the west: St. Louis, Missouri. Lying next to the mighty Mississippi River, this city is home to over 300,000 residents. 


Temperature

The official weather station for the city is located at the St. Louis Lambert International Airport, northwest of the city, and has been in operation since 1929. These airport stations are typically used for long term analysis, and when looking at a climatological average of temperature information, they usually follow a “normal distribution.” This distribution shows temperatures typically increase up to a certain point, and then decrease back down. This can be seen in the graph below as a “bell” shaped curve (or for St Louis, an “arch” shape). According to a 30 year climatological average (smoothed bars below), daily maximum temperatures typically peak in early to mid July, at around 89.3 degrees fahrenheit. Temperatures in the afternoon are typically between 85 and 89 for most of July and August, before they begin to drop around September. 

The figure below also depicts current temperatures for the year 2018. Daily maximum temperatures (red line) and minimum temperatures (blue line) are compared against the 1981-2010 climatology (smoothed dark bars) and its extreme (jagged light bars) values, indicating the hottest / coldest it ever recorded on that particular day. For 2018, maximum and minimum temperatures have fluctuated from warmer than normal, to cooler. A good portion of March and April saw cooler than normal conditions, while May and June saw slightly above normal conditions. By the end of August, the year-to-date temperature averages have been around normal, only 0.3 degrees above the 1981-2010 mean.

At the time of writing, there have been four days the maximum temperature broke a record (one in February, three in May) and seven times the overnight minimum temperature was at its warmest. As expected, July holds the warmest temperature records for the city, with extreme daytime max temperatures well into the 110s. Most of the coldest nights ever recorded occurred in either December or January, and range between -10 and -20 Fahrenheit. 

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Precipitation and Snowfall

St Louis typically sees 40 to 45 inches of rainfall per year. Most of that precipitation occurs in May, although can vary year to year. The graph below attempts to place the current year (2018) against its other years. At the time of writing, there has been 30 inches of rain, which is 3 inches above what is typically seen at this time (27 inches). This can be depicted as either a precipitation anomaly (+3 inches) or a percent of normal (111%). The dark blue line shows the wettest year on record, which occurred just recently in 2015. Part of this was due to 9.18” falling from December 26th to 28th, cementing that year as the wettest on record.

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With regards to snowfall. St Louis typically sees about 17.7 inches each year. As expected, most of it falls during the winter months of December, January, and February, although it has happened in other months. The snowiest day on record occurred in March 2013, when 12.4 inches fell on the 24th, which has been dubbed the Palm Sunday Winter Storm. The highest two day event occurred during the Blizzard of 1982, when 13.9 inches fell on January 30th and 31st.  


Weather Event: 2012 Drought and Heat Wave of June and July

The 2012 drought has been noted as one of the more severe droughts this century. It affected much of the Midwest and Great Plains, including St Louis. According to the United States Drought Monitor, parts of the city saw severe drought conditions (D2 classification) from June to October. They also saw extreme drought conditions (D3 classification) in July and August.

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While drought is usually synonymous with little precipitation, it can also bring in lots of heat. During the end of June 2012, a large area of high pressure descended over the region. This is sometimes known as a “Heat Dome”, where the jet stream is well to the north of the United States, and creates this stationary area of higher pressure, inhibiting rainfall, and helping to increase temperatures. Until something pushes that ridge away, it will continue to stay there. This created some really warmer than normal temperatures, as seen by the animation below:

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Between June 27th and July 7th, St Louis saw extreme temperatures both during the day, and overnight, as seen by the table below. Values that tied or broke records are noted, and are stll the records to this day. St Louis saw 10 straight days of maximum temperatures greater than 100F, and 4 straight days where the overnight minimum temperature was greater than 80. This did not bode well for heat health, as 18 people died during this event.

  • June 27th: 99 / 66
  • June 28th: 108 / 79
  • June 29th: 106 / 77
  • June 30th: 105 / 78
  • July 1st: 102 / 79
  • July 2nd: 100 / 77
  • July 3rd: 101 / 76
  • July 4th: 105 / 83
  • July 5th: 105 / 83
  • July 6th: 106 / 83
  • July 7th: 107 / 83

For a more informative analysis of the event, check out this report produced by the National Weather Service in St. Louis, MO.


Other Notable Weather Statistics for St. Louis

To end, let's provide some 1-day extremes for the city:

  • Highest Maximum Temperature Ever Recorded: 115F on July 14th, 1954
  • Lowest Minimum Temperature Ever Recorded: -19F on January 18th, 1930
  • Highest 1-day Precipitation Ever Recorded: 5.59 inches on May 16th, 1995
  • Highest 1-day Snowfall Ever Recorded: 12.4 inches on March 24th, 2013

And with that, it is hoped that the climatology of St. Louis is “Better Known.” If you would like to see your city highlighted in the next edition of "Better Know a City Climatology," please provide a comment below.