Saint Louis is located at the confluence of the Missouri and Mississippi Rivers and near the geographical "center" of the United States. Thus, with a somewhat modified continental climate, the area experiences the changes of a four-season climate without the undue hardship of prolonged periods of extreme heat or high humidity. To the south is the warm, moist air of the Gulf of Mexico, and to the north, in Canada, is a favored region of cold air masses. The alternate invasion of Saint Louis by air masses from these sources, and the conflict along the frontal zones where they come together, produce a variety of weather conditions.

Winters are brisk and stimulating, seldom severe. Records since 1871 show that temperatures drop to zero or below degrees F an average of two or three days per year. Maximum temperatures remain as cold as 32 degrees or lower less than 20-25 days in most years, The record low temperature recorded by the National Weather Service was -22° on January 5, 1884.

Snowfall has averaged less than 20 inches per winter season since 1930 and has varied from a mere 0.7 of an inch in 1931-32 to a record 67.6 inches in 1911-12. More recently, during the winter of 1977-78, 66.0 inches fell giving Saint Louis its second largest seasonal snowfall of record.

The long-term record for Saint Louis (since 1871) indicates that maximum temperatures of 90° or higher occur an average of 35 to 40 days per year. Extremely hot days of 100° or more are expected on no more than about five days per year. The highest temperature on record is 115° read at Lambert Airport on July 14, 1954.

Normal annual precipitation for the Saint Louis area, based on the average for the period 1941-70, is a little over 35 inches, but 68.83 inches was recorded in 1958, and as little as 20.59 inches in 1953. The three winter months are the driest, with an average total of about six inches of precipitation. The spring months of April to June are normally the wettest with normal total precipitation of nearly 12 inches. From the middle of summer in July into the fall, it is not unusual to have extended periods of one to two weeks or more without appreciable rainfall.