By Wendy Langhans
“Muggy” is not a word I would normally use to describe summers in our Santa Clarita Valley. “Hot”, yes, but not “muggy”. Of course, muggy depends on what you are used to, but in the continental U.S., it usually begins to feel muggy when the dew point is above 65 °F . For me, the air is muggy is when I begin to “feel” the thickness of the air and the sweat on my skin refuses to evaporate.
And I could feel the air last Tuesday in Minneapolis. The dew point at the airport reached a whopping 82 degrees, the highest recorded dew point since they began taking measurements there in 1945. According to one source , “A handful of locations in the United States have seen dew points as high as 90 °F, especially in Florida and Louisiana.” As a point of comparision, other sources claim the highest dew point  ever recorded was 95 °F. This occurred in Dhahran, Saudi Arabia at 3PM on July 8, 2003.
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But what, exactly, is the dew point? And how is it related to “relative humidity” and the “heat index”? You can always check out the National Weather Service glossary , but here’s a quick rundown:
1) Dew point is a technical measure of the amount of water vapor in the air, specifically, the temperature at which the air becomes saturated with moisture. It is the best “absolute” measure of water vapor in the air. To see a fuller explantion of why this is so, go here . When the surface air temperature reaches the dew point, fog forms, just like in this photo taken last week in Wisconsin.
2) Relative Humidity is another technical measurement: the amount of water vapor in the air relative to the maximum amount of water vapor the air can hold. But the hotter the air, the more water it can hold, so the maximum amount of moisture is dependent on the air temperature. So this measurement is not the best “absolute” measure of water vapor in the air. It’s a function of both air temperature and amount of water vapor.
3) The Heat Index is a human-centric measurement. It is the temperature the body feels when air temperature and relative humidity are combined. Our bodies respond to higher temperatures by sweating, but the higher the relative humidity, the more difficult it is for sweat to evaporate. For more information about the Heat Index, the National Weather Service has provided  an explanation and chart, as well as a printable safety and first-aid brochure .
After spending a bit of time on the tarmac in Minneapolis, I’m glad to be back in the SCV. The Weather Underground  forecast for Friday afternoon is 86 °F, with a dew point of 51 and a relative humidity of 33%. And compared to Tuesday’s Heat Index of 118 °F in Minneapolis, our Heat Index is projected to be a more comfortable 84 °F. Whew!
Upcoming Outdoor Events:
Saturday, August 13th, 7:30 - 9:30 PM, Full Moon Hike at Towsley Canyon. Follow that adventurer’s spirit and step into the night on the ruggedly beautiful Wiley Canyon Trail. Look and listen for wildlife in the light of a summer full moon on this moderate hike. Meet at Towsley Canyon’s front parking lot. Easy walk, 2 hours. Meet at Towsley Canyon’s front parking lot. For directions and trail maps, click here .
Trail Maintenance Schedule. Come join our volunteers as they help maintain our trails. Contact Steve at firstname.lastname@example.org  for time and place.
Wednesday mornings, July 6, 13, 20, 27.
Saturday mornings, July 9 & 23.
You can listen to stories like this every Friday morning at 7:10 a.m. on "The SCV Outdoor Report", brought to you by your hometown radio station KHTS (AM1220) and by the Mountains Recreation and Conservation Authority.
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