As summer approaches, a crucial element in determining how we feel in the heat is the dew point, which signifies the temperature at which air becomes saturated with moisture. When the actual temperature and dew point align, relative humidity reaches 100 percent, but such conditions are infrequent.
For example, both a temperature and dew point of 30 degrees and one of 70 degrees lead to relative humidity levels at 100 percent, yet the sensation of warmth can vary widely. Thus, focusing on the dew point is a more effective measure of moisture levels in the air. Meteorologists underline its importance by quantifying moisture in the air in grams per kilogram.
The relationship between dew point and our bodily comfort is crucial. The higher the moisture content in the air, the less efficient our skin becomes at losing moisture, which means sweating has a diminished effect, making us feel hotter. Conversely, lower dew points promote higher evaporation rates, allowing us to cool off more effectively even on hot days, such as those experienced in desert climates, where heat may feel less oppressive due to lower humidity levels.
Generally, when dew points are below 55 degrees, most individuals find the weather comfortable, even amidst rising temperatures. As the dew point creeps into the range of 55 to 60 degrees, the air begins to feel more summery, losing a certain crispness, but comfort levels don’t plummet. Particularly in early summer, people may find the humidity unfamiliar, leading to some discomfort. However, once dew points reach the lower 60s, a noticeable change occurs, with many people remarking about the stickiness in the air.
Dew points in the mid-60s push the boundaries of comfort for a larger number of individuals, a trend that continues as the readings increase into the upper 60s, especially when temperatures rise above 80 degrees. As humidity levels soar, the number of individuals who enjoy the combination of heat and humidity declines. When dew points surpass 70 degrees, particularly under high temperatures, air conditioners become essential for comfort, and outdoor activities decrease, leading to increased complaints about the oppressive humidity.
Each summer, we inevitably experience several days characterized by discomfort due to dew points pushing into the mid-70s or nearing 80 degrees, creating quite a miserable outdoor experience. Alarmingly, the ongoing impacts of climate change have led to a rise in the frequency of high dew point days, making summer heat feel even more suffocating.
Data indicates that dew points begin to rise sharply during June, reliably exceeding 60 degrees by the end of the month on 75 percent of days. This trend intensifies through mid-July to mid-August, with many days experiencing dew points at or above 60 degrees, creating a core period of humidity that greatly impacts comfort levels.
As we now enter the season of heightened dew points and increasing heat, it will be the air conditioning units doing the heavy lifting in terms of providing comfort rather than any change in air mass. So, as summer unfolds, we brace ourselves for the impact of moisture on our day-to-day experiences.
Welcome to what promises to be a humid summer.
image source from：https://www.bostonglobe.com/2025/06/05/metro/dew-point-temperatures-explained-boston-90-degrees/
