Monday, March 31, 2014

Episode 207 (3-31-14): Air, Water, and Fire

Click to listen to episode (2:50)


From the Cumberland Gap to the Atlantic Ocean, this is Virginia Water Radio for the week of March 31, 2014.

This week, we feature three mystery sounds.  Have a listen for about 25 seconds, and see if you can guess what current weather-and-water “season” connects these sounds.  And here’s a hint: you can match ‘em up if you spring into action.


If you guessed Spring Wildfire Season, you’re right!  The Virginia Department of Forestry designates February 15 to April 30 as spring wildfire season, when the Commonwealth typically experiences the most wildfires and when open-air burning is permitted only after 4 p.m. and only under certain conditions.  What’s special about this time of year?  Our sounds identify the key factors and actors.  First, you heard strong, dry spring winds—effective at spreading fire—blowing through dried leaves—effective at catching fire.  Second, you heard a sling psychrometer, an old-fashioned but still valuable tool for measuring relative humidityHigh relative humidity makes summer days feel sticky, but typically low relative humidity in spring increases fire potential.  And third, you heard matches being struck and then doused, emphasizing that most wildfires in Virginia are caused by humans, with open-air burning causing about one-third.  So especially in the weeks around April 1, there’s no foolin’ about the dangerous combination of dry air, dry vegetation, and a fire source.  Thanks to Phillip Manuel of the National Weather Service office in Blacksburg for providing the sound of a sling psychrometer.

For other water sounds and music, and for more Virginia water information, visit our Web site at, or call us at (540) 231-5463.  From the Virginia Water Resources Research Center in Blacksburg, I’m Alan Raflo, thanking you for listening, and wishing you health, wisdom, and good water.

[All Internet addresses mentioned were functional as of 3/31/14]

Top and middle photos: Sling psychrometer used for measuring relative humidity.  The tool measures the difference in temperature on the dry thermometer on the left compared to the wet thermometer (its bulb is stuck into wet cotton) when the device is slung by the attached rod, as in the middle photo.  The humidity calculator (ruler at top of photo) gives the relative humidity based on the temperature difference.  Bottom photo: Belt weather kit used for field measurements needed to assess fire potential and predict wildfire behavior.  Photos courtesy of Phillip Manuel, Fire Weather Program leader at the National Weather Service Forecast Office, Blacksburg, Virginia.

Acknowledgments, Sources, and More Information: The sound of a sling psychrometer was recorded by Phillip Manuel at National Weather Service (NWS) Blacksburg Forecast Office, 3/28/14.  Thanks to Mr. Manuel for the sound and for information on measuring relative humidity, and thanks to David Wert, Meteorologist-in-Charge at the Blacksburg office, for his assistance with this episode.Information on Virginia’s spring wildfire season was taken from the Virginia Department of Forestry’s “Wildfire and Fire Safety” Web site at

National Weather Service forecast maps of relative humidity and several measurements are available online at  The site also provides brief definitions of the different weather measurements.

A map of current relative humidity readings around Virginia is available online at  The map is provided by Air Sports Net, a Web site produced by MoonShade Media LLC (

To reinforce the concepts of wind, relative humidity, and dry vegetation contributing to wildfire potential, click here for an excerpt (1 min./5 sec.) from a “Red Flag Warning” issued on March 11, 2014, by the NWS office in Blacksburg and broadcast that morning on NOAA Weather Radio.

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