May in review: Temperatures were deceivingly warm
Lots of cloud cover resulted in cool days but warm nights
The month of May, which ended Saturday, seemed unusually gray and cool in East Tennessee. How did it actually stack up? Believe it or not, slightly warmer than usual.
The typical average temperature in Oneida during the month of May is 63.1°. May 2025 saw an average temperature of 63.3°, which is just barely above average.
That number is deceiving, however. The same cloud cover that resulted in so many gray days in May also kept temperatures up at night. Cloudy days are typically cooler than clear days, and clear nights are typically cooler than cloudy nights. That’s because cloud cover serves as an insulator — blocking some of the sun’s penetrating rays during the day, while also preventing heat from escaping back into the atmosphere at night.
As a result, our average nighttime temperature in May was 53.3° — a full three degrees above average.
By contrast, our daytime temperature during the month of May averaged 73.3° — a little more than 2.5 degrees below average. When most people perceive temperatures being warm or cool, they’re basing that perception on what’s happening during the day. That’s why the overall average temperature for May was deceptive: we saw a lot of relatively cool days, but they were offset by a lot of relatively warm nights — again, due to excessive cloud cover that persisted for most of the month.
The hottest temperature we experienced in May was 83°. The temperature hit 80° or hotter six different days in Oneida during the month of May, the fewest this decade. The most was in 2022, when we hit 80° or warmer 15 different days in May.
That’s expected to change this week, with temperatures potentially getting to 80° as soon as Monday, and almost certainly getting into the 80s Tuesday, Wednesday and Thursday.
Oneida typically sees its first day of temperatures warmer than 85° by May 19, though it hasn’t happened so far this year.
We typically see our first 90° temperature during the month of June. The average date of the first 90° day in Oneida is June 19, dating back to the 1950s. (The latest it’s ever happened was in 2003, when the first 90° day didn’t happen until Aug. 25.)