temperature · United States
Chicago, Illinois
January mean temperature
Modelled demonstration series · not observed data
A cold anomaly on a warming wall is not a contradiction and it is not a rebuttal. Severe cold outbreaks come from Arctic air escaping south when the polar vortex is disrupted; a warming Arctic changes the behaviour of that vortex. The honest summary is that the average is climbing while the extremes on both tails stay violent.
75 years, modelled
Same reading, two normals
| Normal | Mean | σ | Pct | Return |
|---|---|---|---|---|
| 1951–1980 | -5.6 °C | −2.80σ | 0.26th | 1 in 390 years |
| 1991–2020 | -4.7 °C | −3.21σ | 0.066th | 1 in 1,500 years |
Today would be the lowest value in the entire 75-year modelled series. Past the series' standing low of -10.8 °C (2012). Nothing about the reading changes between rows — only the yardstick.
The season here
Midwestern Januaries swing hard. A cold month here usually means a displaced polar vortex delivering Arctic air far south of where it belongs.
Where this series comes from
MODELLED SERIES — not observed. Parameters set from published Chicago Midway/O'Hare January climatology. The 75 annual values are synthesised by the seeded generator.
Every number on this page comes from a modelled series: 75 annual values synthesised by a seeded generator from published climatological parameters for Chicago, Illinois. It shows how anomaly reasoning works. It is not a measurement and must not be cited as one.
How to read σ
σ counts standard deviations from this place's own normal. The sigma guide · return periods.
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