Monday, October 17, 2016

Episode 338 (10-17-16): Rainfall Dimensions

Transcript of audio, notes on the audio, images, and additional information follow below.

All Web addresses mentioned were functional as of 10-7-16.


From the Cumberland Gap to the Atlantic Ocean, this is Virginia Water Radio for the week of October 17, 2016.

SOUND – ~ 3 sec

This week, we drop in on a familiar kind of conversation: two people talking about the weather.  In this case, the weather occurred the last week of September 2016 in Blacksburg, Va.; it was quite unusual; and it generated some questions about several key dimensions of rainfall.  Let’s have a listen.

SOUNDS - ~ 3 sec

Kriddie: Hey, Alan. Whatcha doin’?

Alan: Hey, Kriddie. I’m checking out the water gushing through that stormwater pipe.  I’ve lived in this neighborhood for 16 years and this is the first time I’ve seen it rain hard enough for water to flow through there!   I’ve had over 3 and a half inches at my house just this afternoon!

Kriddie: Yeah, and it’s still coming down pretty hard!   I’m goin’ inside!   Let’s talk about it later!

SOUNDS - ~ 3 sec

Alan: Hey, Kriddie!  Wanna talk some more now about all that rain we’ve been having?

Kriddie: You bet!   Whatcha got?

Alan: Well, that rain on Monday was just the beginning!  With that day plus the past three, I’ve measured over 10 inches at my house.

Kriddie: Whew!  I knew we’d gotten a lot, but I didn’t think it was that much.

Alan: Yeah, and get this.  The National Weather Service Office in Blacksburg is only about 3 miles from my house, and their preliminary data show only about 5 or 6 inches for the same period.

Kriddie: Yeah, storms can be really variable.  That’s why you need a lot of rain gauges to get an accurate average rainfall for an area.   I’ve read that the Appalachian mountain region particularly can get some really intense rainfall, like what caused that flash flooding in Madison County, Virginia, in June 1995.  I understand that was a 1000-year storm for the Rapidan River watershed.

Alan: What do you mean by that?  You mean a rainfall like that comes only once in 1000 years?

Kriddie: No, actually not.   It means there’s a 1 in a 1000 chance, or probability, that such a rainfall could be exceeded in any given year.  Scientists use historical records to calculate probabilities that a certain area will have a rainfall of a certain volume over different durations, like 24 hours, or 2 days, or 4 days.  And, in fact, I just happen to have a table of values for Blacksburg right here.  OK, let’s see: you measured a volume of over 10 inches, duration of 4 days—that works out to close to a 500-year storm, or a 1-in-500 probability in any year.  Not your usual amount of rain!

Alan: Wow—volume, duration, frequency, probabilities: I never realized all the dimensions to measuring rain!

Kriddie: Yep, and all part of deciding how big that stormwater pipe needed to be!

Alan: Hey, speaking of rain and its dimensions, I just got this new music from my friend Torrin Hallett, a student at Oberlin College and Conservatory in Ohio.  It’s called “Rain Refrain.”  Wanna listen for about 30 seconds?

Kriddie: Sure, then I’m off before it starts raining again!

MUSIC - ~ 30 sec


For more Virginia water sounds, music, and information, visit us online at, or call us at (540) 231-5463.   Virginia Water Radio is produced by the Virginia Water Resources Research Center, part of Virginia Tech’s College of Natural Resources and Environment.  Thanks to Stewart Scales for his banjo version of Cripple Creek to open and close the show.   In Blacksburg, I’m Alan Raflo, thanking you for listening, and wishing you health, wisdom, and good water.


Thanks to Kriddie Whitmore, a graduate student in the Virginia Tech Department of Forest Resources and Environmental Conservation, for lending her voice and suggestions to this episode.

“Rain Refrain” is copyright 2016 by Torrin Hallett, used with permission.  Click here if you’d like to hear the full piece (43 seconds).  In 2016-17, Torrin is a fourth-year student at Oberlin College and Conservatory in Oberlin, Ohio, majoring in horn performance, music composition, and math major.  More information about Torrin is available at his Web site,  Thanks very much to Torrin for composing the piece for Virginia Water Radio.

Thanks to Kevin McGuire, associate director of the Virginia Water Resources Research Center, for his help with this episode.

The sound of water flowing through a stormwater pipe was recorded in Blacksburg, Va., on September 26, 2016, 6:45 p.m., at the same location as the private-residence rainfall amounts mentioned in this episode (see below under Extra Facts for those rainfall measurements).

Stormwater drainage pipe flow in Blacksburg, Va., 6 p.m. on September 26, 2016, recorded for the audio in this episode of Virginia Water Radio.

Storm clouds north of Blacksburg, Va., 7 p.m. on September 26, 2016.

Stormwater detention pond in Blacksburg, Va., September 28, 2016.

Stormwater drainage ditch in Blacksburg, Va., September 29, 2016.

Debris along fence indicating recent high water in Stroubles Creek on the Virginia Tech campus in Blacksburg, Va., October 1, 2016.


Rainfall observations at National Weather Service’s (NWS) Blacksburg Forecast Office for Sept. 26-29, 2016 (preliminary data—that is, still needing official verification—as of 10/7/16)
Sept. 26 – 1.25 inches
Sept. 27 – 0.54 inches
Sept. 28 – 1.02 inches
Sept. 29 – 2.80 inches
9/26-9/29 4-day total = 5.61 inches

Rainfall Observations at the residence of Alan Raflo, Virginia Water Radio host, about 3 miles north of the NWS Blacksburg Forecast Office
Sept. 26 – 3.8 inches
Sept. 27 – 1.4 inches
Sept. 28 – 1.5 inches
Sept. 29 – 3.7 inches
9/26-9/29 4-day total = 10.4 inches.

A 4-day-duration rainfall of 10.4 inches at this location has a return period estimated at 500 years, that is, a 1 in 500 probability of exceedance in any given year, according to the National Weather Service/Hydrometeorological Design Studies Center, “NOAA Atlas 14 Point Precipitation Frequency Estimates: Va,” online at

Madison County, Va., Rainfall in June 1995
On June 27, 1995, the Rapidan River basin received a basin-wide average rainfall of 344 millimeters, or about 13.5 inches, according to Michael D. Pontrelli, et al., 1999, “The Madison County, Virginia, Flash Flood of 27 June 1995,” Weather and Forecasting (American Meteorological Society), Jun. 1, 1999.    According to the NOAA precipitation frequency estimates document mentioned above, a one-day-duration rainfall of 13.5 inches at that location had a 1000-year return period or 1 in 1000 probability of exceedance in any given year.


Used for Audio

Richard H. McCuen, Hydrologic Analysis and Design (Third Edition), Pearson/Prentice Hall, Upper Saddle River, N.J., 2005.

Kevin Myatt, Complex storm system to continue bringing showers/storms to SW Virginia, Roanoke Times, 9/27/16; and One spinning vortex slowly exits as another lingers ominously offstage, Roanoke Times, 9/30/16.

National Weather Service/Blacksburg, Va., Forecast Office, “Observed Weather Reports,” online at

National Weather Service/Hydrometeorological Design Studies Center, “NOAA Atlas 14 Point Precipitation Frequency Estimates: Va,” online at

Michael D. Pontrelli, et al., 1999, “The Madison County, Virginia, Flash Flood of 27 June 1995,” Weather and Forecasting (American Meteorological Society), Jun. 1, 1999.

James A. Smith et al., 2011, “Extreme rainfall and flooding from orographic thunderstorms in the central Appalachians,” Water Resources Research, Vol. 47.

For More Information about Virginia Rainfall Events

Community Collaborative Rain, Hail, and Snow Network (CoCoRaHaS), “Virginia Daily Precipitation Reports,” online at

Associated Press, One-day Record 4.39 Inches of Rain Falls in Blacksburg, as published by WHSV TV-Harrisonburg, Va., 9/30/15; and Virginia Water Resources Research Center/Virginia Water Central News Grouper, “Heavy Rainfall and Flash Flooding in Late September and Early October 2015 — Information Sources,” 9/29/15.  These sources cover a heavy rainfall in late September 2015, a year prior to the subject of this Water Radio episode.

National Weather Service, “Observed Weather Reports”: Morristown, Tenn., Forecast Office (serving far southwestern Virginia), online; Baltimore-Washington Forecast Office, online at; and Wakefield, Va., Forecast Office, online at

National Weather Service/Advanced Hydrologic Prediction Service, online at, providing maps of precipitation nationwide or by state, with capability to show county boundaries, and archives available for specific days, months, or years.

National Weather Service/Storm Prediction Center, online at, providing daily maps and text for preliminary reports of severe thunderstorms, tornadoes, and hail.

Southeast Regional Climate Center (Chapel Hill, N.C), online at, providing maps of total precipitation and percent of normal precipitation for the past 7, 30, 60, or 90 days.


All Water Radio episodes are listed by category at the Index link above (

For other episodes related to weather, please see the “Weather/Natural Disasters” category at the Index link. Please also see the following specific episodes related to rainfall and flooding:
EP86 – 10/31/11 (Historic-record water level marker dedication at New River);
EP192 – 12/16/13 (Nelson County in 1969);
EP272 – 6/29/15 (Madison County in 1995);
EP328 – 8/8/16 (flash flooding in general).


SOLs at various grade levels that call for “examining the relationship of music to the other fine arts and other fields of knowledge.”

Grades K-6 Earth Patterns, Cycles, and Change Theme
2.7 – Weather and seasonal changes affecting plants and animals.
3.9 – Water cycle, including sources of water, energy driving water cycle, water essential for living things, and water limitations and conservation.

Grades K-6 Earth Resources Theme
4.9 - Va. natural resources, including watersheds, water resources, and organisms.

Grades K-6 Interrelationships in Earth/Space Systems Theme
2.6 – identification of common storms and other weather phenomena.
4.6 – weather conditions, phenomena, and measurements.
6.6 – properties of air and structure of Earth’s atmosphere; including weather topics.

Grades K-6 Living Systems Theme
6.7 - natural processes and human interactions that affect watershed systems; Va. watersheds, water bodies, and wetlands; and water monitoring.

Grades K-6 Matter Theme
6.6 – Properties of air (including pressure, temperature, and humidity) and structure/dynamics of earth’s atmosphere.

Life Science Course
LS.11 - relationships between ecosystem dynamics and human activity.

Earth Science Course
ES.8 - influences by geologic processes and the activities of humans on freshwater resources, including identification of groundwater and major watershed systems in Virginia.
ES.12 – weather and climate.

Social Studies
World Geography Course
WG.2 - how selected physical and ecological processes shape the Earth’s surface, including how humans influence their environment and are influenced by it.

Virginia’s SOLs are available from the Virginia Department of Education, online at