Illinois · 178 m elevation

Barometric Pressure in Chicago, IL

• 30.03Average pressure (inHg, sea level)
• 233.7Swing days a year · 9th of 50
• 133.1Big-swing days a year (≥10 hPa)
• 136.4Significant 24h drop days a year

Overview

Chicago averages 233.7 significant pressure swing days per year, ranking 9th of 50 US cities. Seasonal patterns, records, and the January 2024 extremes.

Chicago's mean sea-level pressure over 2015–2024 was 30.03 inHg (1017.1 hPa), with a median of 30.02 inHg (1016.7 hPa). Most of the time the barometer stays inside a fairly ordinary band: the 5th percentile is 29.68 inHg (1005.1 hPa) and the 95th is 30.42 inHg (1030.0 hPa). What separates Chicago from most of the country is not how far pressure travels but how often it moves.

Across 50 major US cities, Chicago ranks #9 for significant swing days — 24-hour changes of at least 0.18 inHg (6 hPa) — at 233.7 per year against a national median of 180.7. It also ranks #9 for big-swing days of 0.30 inHg (10 hPa) or more, logging 133.1 per year versus a median of 86.1, about 1.55 times the national norm. Standard deviation is 0.22 inHg (7.59 hPa), ranking #13. Chicago sits in the same tier as Milwaukee (242.7 swing days, #5) and Detroit (239.3, #8), and reaches 83% of national leader Denver's 281.6. Against Atlanta it runs 2.0 times the swing days, against Los Angeles 5.1 times, and against Miami 11.8 times.

The city sits at 178 meters (584 feet), and that elevation matters for anyone reading a barometer at home. Mean station pressure — the actual weight of air at the surface, uncorrected — averages 29.40 inHg (995.5 hPa), roughly 0.64 inHg (21.6 hPa) below the sea-level-adjusted figure used in forecasts. An instrument showing 29.4 in Chicago is not reading low; it is reading uncorrected.

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, Chicago is a high-frequency environment. A typical 24-hour change is 0.12 inHg (4.1 hPa), but the 95th percentile reaches 0.46 inHg (15.6 hPa), and 136.4 days a year are drop days — significant 24-hour falls, the direction many pressure-sensitive people report as a trigger. Chicago's 133.1 big-swing days a year outnumber the median city's 86.1 by more than half again.

The seasonal split matters more here than the annual average. January alone averages 16.6 drop days, with December at 16.5 and February at 16.4 — roughly one significant fall every other day through midwinter. August averages 4.0 drop days and July 4.2. Normalized to a daily rate, a Chicago January runs at about 0.88 swing days per calendar day, a faster clip than Denver's year-round average; a Chicago August runs closer to the pace of a mild West Coast market. Late June through mid-September is the settled stretch; November through March is when conditions many pressure-sensitive people report as triggers occur most often.

In national terms, Chicago's swing-day count is 11.8 times Miami's, 5.1 times Los Angeles's, and about 1.29 times the median across the 50 cities studied. Its deepest 24-hour drop, 1.20 inHg (40.6 hPa), ranks #12 nationally — steep, though short of Boston's 1.52 inHg (51.5 hPa). Milwaukee and Detroit offer essentially the same pressure profile, so a substantially lower swing frequency means looking well south or west, toward cities like Atlanta (115.6 swing days), Houston (107.3), or Phoenix (75.8). These are statistical associations reported by some pressure-sensitive people, not a forecast of how any individual will feel.

Seasonal patterns

Chicago's annual volatility ranking undersells winter and oversells summer. December is the most turbulent month, with 27.5 significant swing days and a monthly standard deviation of 0.27 inHg (9.27 hPa). January is nearly identical in frequency at 27.4 swing days and carries the year's widest spread at 0.29 inHg (9.83 hPa). Summed across December, January, and February, the city logs 80.1 swing days — 2.7 times the 29.8 recorded across June, July, and August.

August is the quiet end of the scale: 8.0 swing days and a standard deviation of 0.12 inHg (3.95 hPa), with July close behind at 0.12 inHg (4.03 hPa). The driver is storm-track geography. In winter the jet stream and the surface lows that ride it converge over the Great Lakes, pushing systems past the city every few days. In summer that track retreats north and the region settles into a flatter, more uniform warm-season pressure field. Monthly means follow the same rhythm, peaking at 30.12 inHg (1019.9 hPa) in January and bottoming at 29.93 inHg (1013.6 hPa) in June.

The extremes are winter events almost without exception. The record low of 28.98 inHg (981.5 hPa) came on January 9, 2024, and the same system produced the sharpest 24-hour fall in the ten-year record — 1.20 inHg (40.6 hPa) ending at 3 p.m. that afternoon. The other four deepest drops all fall in January or February: 1.10 inHg (37.2 hPa) on January 18, 2020; 0.99 inHg (33.6 hPa) on January 10, 2017; and 0.97 inHg (33.0 hPa) on both January 8, 2015 and February 24, 2019. The record high, 30.96 inHg (1048.5 hPa), came on February 9, 2019. The largest 24-hour rise was 1.18 inHg (40.0 hPa), and the fastest six-hour fall was 0.51 inHg (17.4 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

• Milwaukee, WI
• Indianapolis, IN
• Detroit, MI
• St. Louis, MO
• Louisville, KY
• Columbus, OH

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