Credit: National Weather ServiceĪt night, when the dew point in the 40s and temperatures are in the 40s, the relative humidity is 100% and it may feel damp to you. Dew points above 65 are downright muggy and even tropical when they reach the 70s. Once the dew point gets between 60 to 65 degrees, it feels sticky or humid. Looking specifically at the dew point temperature, the general rule of thumb is that dew points in the 50s or lower is very comfortable during the warm summer months. The farther apart they are the lower the relative humidity. As you can see from these examples, the closer the temp is to the dew point, the higher the relative humidity. It would feel much more “Humid” on the 80 degree day with 50% relative humidity than on the 30 degree day with a 100% relative humidity. For example, a temperature of 30 and a dew point of 30 will give you a relative humidity of 100%, but a temperature of 80 and a dew point of 60 produces a relative humidity of 50%. The higher the rh % and air temperatures, the more you sweat, but many times, relative humidity can be misleading. This directly affects how “Comfortable” it will feel outside, as seen by this heat index chart. The higher the dew point number, the greater the amount of moisture is in the air. Basically, both relative humidity and dew point measure how much water vapor is in the air however, dew point is simply a measure of how much moisture is in the air at a given time and rh is the ratio between the temperature and dew point temperature. Over the many years that I have been showing these parameters, there is always confusion into what the dew point means and how that relates to relative humidity. "We don't get a lot of it.With the middle of summer in full view, daily temperatures increasing, and higher humidity levels seemingly each and every passing day, I wanted to clear up some confusion when it comes to the terms relative humidity and dew point temperature.When showing the current conditions daily, meteorologists usually have these items on the map…Temperature, wind, relative humidity and dew point. More comfortable air will move in by early next week, with northwest winds helping cool temperatures to around 80 degrees by Monday and Tuesday.įor Joe Eichden, another downtown worker, a few muggy days are just fine. But "it will be feeling downright tropical through this weekend," the weather service said. The dangerous heat will subside slightly Thursday and Friday as temperatures slide back to 89 degrees and 85 degrees, respectively. Wednesday marks the 12th time this year the mercury has hit 90 degrees or higher in the metro, the weather service said. That was set on July 30, 1999, in Red Wing, when the dew point reached 84 degrees and the temperature hit 97 degrees, the Minnesota State Climatology Office said. The state record for the highest heat index is 127 degrees. The highest dew point of 82 degrees occurred at 3 p.m. The metro area recorded its highest heat index 52 years ago on July 11, 1966, at 119 degrees. "Drink plenty of fluids, stay in an air-conditioned room and out of the sun, and check up on relatives and neighbors," the weather service's heat advisory read. On Wednesday, the weather service was predicting heat indexes in the 95 to 105-degree range, conditions ripe for heat illnesses such as cramps, strokes and exhaustion. The higher the dew point, the muggier it will feel. The long and the short of it is, if you want a real judge of how "dry" or "humid" it will feel outside, look at the dew point instead of the humidity level. The combination of dew points, humidity and temperature form what's called a heat index, or what it feels like to be outside. And in the 80s, well, downright oppressive. Cross over into the 70s and it feels tropical. As dew points rise into 60s, it begins to feel juicy. "It's one of the most confusing things when the weather gets hot," said Michelle Margraf, a meteorologist with the National Weather Service in Chanhassen.Īs air gets warmer, it can hold more water. It's even tough for the weather folks to explain. Assuming the water vapor content stays the same, of course. When temperatures go down, humidity levels go up. In short, when the temperature goes up, the relative humidity goes down. When the air temperature drops below the dew point, water vapor comes out of the atmosphere, usually in the form of fog or precipitation. A high dew point can make a summer day feel tropical.
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