document updated a month ago, on Sep 17, 2024

sites that let you see the barometric history (the opposite of a forecast)

Barometric pressure conversion table.
The range of "normal" pressures goes from ~1000 to 1030 mb, though it can go outside that once in a while.
This corresponds to ~29.50 to 30.25 inHg.

TidesAndCurrents.noaa.gov
- Calumet Harbor, IL station — it's the third chart down, the one that says "Millibars" on the left side. (Calumet Harbor is located in Chicago)
- it defaults to showing the last ~36 hours, but you can change it — go down to the date range at the bottom, then click Update > Plot
weather.gov — Time Series Viewer — Sea Level Pressure
- O'Hare station (Select Graph > Sea Level Pressure (millibars) or Altimeter Setting (inches of mercury))
AlertEagle.com
- Chicago Heights, IL station
BarometricPressure.app — They try really hard to sell you an app, and the historical data is only accessible on the desktop.
- Chicago station
- it graphs the last 3 days (last 72 hours)
mesowest.utah.edu (extended directions on Reddit)
- O'Hare station
wpc.ncep.noaa.gov
- last 3 days, last 7 days
Wunderground.com/history/
- O'Hare station — scroll down to "daily observations", then scroll right to the "pressure" column