Climate twins of St. Charles, IA
These are the US cities whose 12-month climate pattern most closely matches St. Charles's. Each "twin" must be at least 140 miles away to avoid trivial near-neighbor matches. Similarity is computed across all 24 monthly metrics (12 average temperatures + 12 average precipitations), normalized so temperature and precipitation contribute equally.
Side-by-side: St. Charles vs its climate twin
Top match: Washington, IA
| Month | St. Charles | Washington | ||||
|---|---|---|---|---|---|---|
| High | Low | Precip | High | Low | Precip | |
| January | 31.7°F | 11.6°F | 0.91 in | 30.2°F | 11.5°F | 1.25 in |
| February | 36.3°F | 15.2°F | 1.42 in | 35.0°F | 15.3°F | 1.56 in |
| March | 49.5°F | 27.1°F | 1.94 in | 48.3°F | 26.5°F | 2.32 in |
| April | 62.1°F | 37.9°F | 3.88 in | 62.0°F | 37.5°F | 3.65 in |
| May | 71.9°F | 49.9°F | 5.58 in | 72.2°F | 49.7°F | 5.11 in |
| June | 81.4°F | 60.0°F | 5.72 in | 81.4°F | 59.8°F | 5.17 in |
| July | 85.5°F | 64.0°F | 4.32 in | 85.0°F | 63.1°F | 4.13 in |
| August | 84.0°F | 61.6°F | 3.90 in | 83.3°F | 60.7°F | 4.18 in |
| September | 77.6°F | 52.4°F | 3.86 in | 77.3°F | 51.4°F | 3.60 in |
| October | 64.8°F | 40.1°F | 3.02 in | 64.2°F | 39.9°F | 3.03 in |
| November | 49.6°F | 27.9°F | 1.85 in | 48.7°F | 27.7°F | 2.23 in |
| December | 36.9°F | 17.4°F | 1.40 in | 35.6°F | 17.9°F | 1.71 in |
How this is computed
Each city is represented by a 24-dimensional vector: 12 monthly average temperatures and 12 monthly average precipitations. Each dimension is z-score normalized across the population of US cities, so that temperature variance and precipitation variance contribute proportionally. Distance between cities is Euclidean. We filter out cities within 2° latitude/longitude (~140 miles) so that "twins" mean climatically similar but geographically distinct — not just the neighboring town. Full methodology →