How Dry We Were!
Posted July 5, 2009
While we saw some rain and thunderstorm potential develop on Sunday, much of the July 4th weekend this year featured sunshine, fair weather clouds and fairly hot, near-normal temperatures. One thing that was definitely missing from the classic central NC Independence Day, though, was humidity. We tend to think of hot, sticky weather as par for the course for this holiday, but this year we had a nice break as both Friday and Saturday featured afternoon dew points in the low to mid 50s.
As a reminder, dew point varies directly with the amount of water vapor in the air, and relates nicely to how we perceive comfort in terms of humidity when the weather is warm or hot. Dew points in the 40s and 50s typically feel quite pleasant, and we really don't notice the air as being humid. Dew points in the 60s usually lead to a bit of a humid feeling, especially the mid 60s and up, while dew points in the 70s usually draw a lot of remarks about how sticky it feels, and it becomes downright oppressively humid when the dew points reach or exceed the mid 70s.
One reason this year seemed so pleasant on the 4th is that we really do tend to have more moisture in the air this time of year. I took a look at our dew point at 3 pm on July 4th over the past 15 years. This year, we were at 53 degrees for dew point at that time of day, and it was only the second time in that 15-year period we had been below 60. The average 3pm dew point over the past 15 years is 65.5 degrees (at the "noticeably humid" level), and four times during that period we've had an afternoon dew point of 73 or 74 degrees, including 1999, which was probably the most uncomfortable, with a 3 pm temperature of 95 and a dew point of 73, which translates to a heat index around 105 degrees.
I did find one July 4th that was even more refreshingly mild and dry than this year - in 1996, the 3 pm temperature was 81, there was sunshine and a nice northwest breeze, and the dew point was an incredibly low 46! Hopefully, a lot of us enjoyed (and appreciated) that day and the one this weekend - they don't come around like that very often!