Best Time to Dive Illinois
Across 4 Illinois dive sites with multi-year conditions history, September historically shows the most favorable days — 96% of sampled days in the good band.
Computed from our own conditions climatology — measured history, not brochure copy. Historical patterns, never a forecast or a guarantee.
Month by month
| Month | Historically favorable days | Water temp | Typical seas |
|---|---|---|---|
| Jan | 83% | — | — |
| Feb | 77% | — | — |
| Mar | 66% | — | — |
| Apr | 61% | — | — |
| May | 80% | — | — |
| Jun | 84% | — | — |
| Jul | 93% | — | — |
| Aug | 92% | — | — |
| Sep | 96% | — | — |
| Oct | 79% | — | — |
| Nov | 78% | — | — |
| Dec | 80% | — | — |
% = share of sampled days scoring in the favorable band, median across 4 sites with at least two years of history. Ringed = historical peak.
How does this compare worldwide? The Most Reliable Diving Months on Earth ranks 61 countries by the same measure.
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