Missouri · 142 m elevation

Barometric Pressure in St. Louis, MO

• 30.04Average pressure (inHg, sea level)
• 193.8Swing days a year · 22nd of 50
• 103.6Big-swing days a year (≥10 hPa)
• 112.3Significant 24h drop days a year

Overview

St. Louis averages 30.04 inHg (1017.4 hPa) and 193.8 significant pressure swing days a year — but 52% of them fall in December through March.

St. Louis sits at 30.04 inHg (1017.4 hPa) on average at sea-level reduction, with a median of 30.03 inHg (1016.8 hPa). Ninety percent of hours over the 2015–2024 record fall between 29.72 inHg (1006.5 hPa) and 30.42 inHg (1030.1 hPa). The standard deviation is 0.21 inHg (7.19 hPa), which ranks #19 of the 50 cities in this survey and sits just above the national median of 6.87 hPa.

By the annual counts, St. Louis is unremarkable: 193.8 significant swing days per year (24-hour change of at least 0.18 inHg / 6 hPa), ranking #22 of 50 against a national median of 180.7, and 103.6 big-swing days (0.30 inHg / 10 hPa or more), ranking #21 against a median of 86.1. Those numbers hide the real story. St. Louis is statistically average for the year and nothing like average within it — winter here behaves like a top-ten volatile city and summer behaves like the Gulf Coast.

One practical note on hardware. The city sits at 142 m (466 ft), and mean station pressure is 29.54 inHg (1000.4 hPa) against the sea-level mean of 30.04 inHg (1017.4 hPa) — an offset of about 0.50 inHg (17.0 hPa). An uncalibrated home barometer reading raw station pressure will show roughly 29.54 inHg when the airport reports 30.04 inHg. Nothing is wrong with the instrument; it simply isn't applying the altimeter correction. Trends and day-to-day changes are identical either way.

Migraine & pressure-sensitivity outlook

• Low — under 6 hPa (0.18 inHg)
• Elevated — 6 to 10 hPa
• High — 10 hPa (0.30 inHg) or more
• Dashed outline = forecast (after today)

Association only. This calendar shows days when pressure changed — or is forecast to change — sharply over 24 hours, conditions associated with pressure sensitivity in some people. It is not a prediction of symptoms, not a diagnosis, and not medical advice. The 30 days of history are there so you can compare the days you actually felt something against what the barometer did. Talk to a clinician about headache or migraine management.

For people who track barometric pressure as a symptom trigger, St. Louis is a calendar problem more than a climate problem. The city logs 112.3 drop days per year — significant 24-hour falls — and 103.6 big-swing days of 0.30 inHg (10 hPa) or more. The distribution is heavily front-loaded: March averages 16.0 drop days, February 15.7, January 15.5, and December 14.8, while July averages 1.6 and August 1.5. Late winter and early spring produce conditions many pressure-sensitive people report as triggers on roughly half of all days; midsummer produces them once or twice a month.

Most days, even in winter, are quiet. The median absolute 24-hour change is just 0.10 inHg (3.4 hPa). The volatility is concentrated in discrete frontal passages: the 95th-percentile 24-hour move is 0.41 inHg (14.0 hPa), and the 5th and 95th percentiles of signed change run -0.32 inHg (-10.7 hPa) and +0.34 inHg (+11.4 hPa). Six-hour moves reach -0.13 inHg (-4.4 hPa) and +0.12 inHg (+4.2 hPa) at those same percentiles. In practice that means a handful of sharp, well-defined events per winter month rather than constant background churn.

For context, St. Louis sees 9.8 times the swing days of Miami (19.8 per year) and 32 times its big-swing days, and 2.3 times Atlanta's big-swing count. It is meaningfully calmer than Chicago (233.7 swing days) and than Kansas City across the state (218.2 swing days, 125.3 big-swing days), and about 69% as active as Denver, the national leader at 281.6. Going south, Memphis logs 147.1 swing days to St. Louis's 193.8 — a 1.32x difference over 250 miles of the same river valley. Anyone comparing locations on this metric should weigh the seasonal shape as much as the annual total: a move to Florida or the desert Southwest cuts the count several-fold, while a move within the Midwest changes it far less.

Seasonal patterns

The seasonal split here is severe. March averages 26.0 swing days per year, January 25.7, February 24.9, and December 24.6. July averages 2.6. That is a tenfold difference between the most and least active months, and December through March alone account for 101.2 of the year's 193.8 swing days — 52% of the annual total packed into four months. Monthly variability tells the same story: the standard deviation runs 0.28 inHg (9.53 hPa) in January and collapses to 0.09 inHg (3.21 hPa) in August.

The driver is the position of the jet stream. In winter the storm track runs directly over the Mississippi Valley, and Plains cyclones and Arctic fronts cross the city in rapid succession, each one dropping and rebuilding pressure by a substantial margin. Monthly means follow the same rhythm: 30.16 inHg (1021.2 hPa) in January, easing to 30.08 inHg (1018.6 hPa) in March and bottoming at 29.93 inHg (1013.7 hPa) in June. By July the jet has retreated north and St. Louis sits under a flat, humid subtropical ridge. Summer storms here bring rain and wind, not large barometric moves.

The extremes confirm the pattern. The record high of 30.98 inHg (1049 hPa) came on January 7, 2015, under a deep Arctic high; the record low of 29.11 inHg (985.9 hPa) came on March 3, 2023. That is a 1.86 inHg (63.1 hPa) span across the decade. All five of the sharpest 24-hour falls landed between December and March: -0.99 inHg (-33.4 hPa) ending January 9, 2024; -0.88 inHg (-29.8 hPa) on January 18, 2020; -0.87 inHg (-29.4 hPa) on December 28, 2015; -0.87 inHg (-29.3 hPa) on February 27, 2023; and -0.85 inHg (-28.9 hPa) on January 8, 2015. The largest 24-hour rise on record was +1.09 inHg (37.0 hPa), and the fastest six-hour fall was -0.44 inHg (-14.8 hPa).

Month by month

Swing days: 24-hour change of at least 6 hPa (0.18 inHg). Drop days: 24-hour fall of at least 6 hPa. Averages per year, 2015–2024.

Records and extremes

Sharpest 24-hour drops, 2015–2024

Nearby cities

• Indianapolis, IN
• Kansas City, MO
• Memphis, TN
• Louisville, KY
• Nashville, TN
• Chicago, IL

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