Cleveland, OH UV Index Today

Two Lake Erie effects pull Cleveland’s ultraviolet in opposite directions, and which one wins depends on the month.

At 41.5 degrees north the noon sun stands about 72 degrees above the horizon at the June solstice and about 25 degrees at the December one. That low winter sun coincides with the cloudiest stretch of the Cleveland year. Erie is the shallowest of the Great Lakes and the one that ices over most completely, but through late autumn and early winter it is still open water, and cold air crossing it picks up moisture on the way to the south shore. Low sun and thick cloud arrive together, which is why the index here sits near the floor for weeks at a time instead of dipping and recovering.

The counterweight sits inland, not downtown. The snowbelt running east and southeast through Geauga and Lake counties holds cover for weeks at a stretch while the lakefront is already back to bare pavement, and on the World Health Organization’s figure fresh snow returns up to 80 percent of the ultraviolet landing on it, close to doubling what a person takes. A clear morning after a snowfall on the inland ridges therefore delivers direct and reflected ultraviolet at once, at an index number the city monitors would not suggest.

In summer the lake works the other way. Air that has crossed cold water reaches the shoreline stable, and the afternoon convection tends to build along the lake-breeze boundary inland rather than over the lakefront itself.