Tuesday, August 12, 2008

Get Dew the Point

This is for weather geeks only. And if you are a real weather geek, you probably already know this, but last week Springfield set an all-time record high dewpoint for the city. From the National Weather Service:
Extremely muggy conditions invaded much of central and southeast Illinois on Monday, August 4th. The dewpoint temperature is commonly used in meteorology to describe atmospheric moisture. It is the temperature to which air must be cooled in order to reach saturation (assuming air pressure and moisture content are constant). In general terms, the higher the dewpoint, the more oppressively humid the air feels. Dewpoints often reach into the low and mid 70s over the eastern half of the U.S. in summertime.

A rare set of factors may have combined on August 4th to produce widespread dewpoints in the upper 70s and lower 80s across central and southeast Illinois. Much above normal rainfall so far this year has led to abundant soil moisture. This has helped local vegetation which usually peaks in evapotranspiration (moisture loss) from mid July to early August. In addition, a warm front established itself across northern Illinois on the afternoon and evening of the 4th. This allowed southerly winds to supply moisture-rich air to the region. Other small-scale effects and local factors may have played a role in producing extremely high dewpoint readings.

Springfield IL established a new dewpoint record of 83 degrees F at 6:52 PM on the 4th. This broke the old record of 82 degrees from August 19, 1993 at 5 PM. The period of hourly records at Springfield dates back to 1948.
We‘ve had more than one really, really humid day this summer. Fortunately, the humidity is leaving us alone for Fair week.

1 comment:

Brian E. Moore, MD said...

That 83 dew point day was weird. There was steam on the windows in the middle of the day. I had never seen that before on a summer day.