Tornado Drought

Tornado Drought in Illinois

One of the side effects of drought is that usually reduces the amount of severe weather we experience in Illinois. This year was a good example of this. After the deadly Harrisburg tornado on February 29, things have been relatively quiet. Here is the monthly breakdown of tornado reports in Illinois, as reported by the NOAA Storm Prediction Center:

  • 2 in January
  • 4 in February
  • 8 in March
  • 0 in April
  • 8 in May
  • 0 in June
  • 1 in July
  • 23 total by the end of July
Severe weather reports in Illinois for 2012 through the end of July. Figure courtesy of NOAA’s Storm Prediction Center.

Tornado Drought in the US

Harold Brooks of NOAA wrote about the US tornado drought on his blog. Here is the figure he used in his post for the US.

The number of tornadoes reported across the US from April 15 to July 31, for 2012 (red line at the bottom) as well for the most active year (2003) and the last widespread tornado-land drought (1988). Figure courtesy of NOAA.

Fort Armstrong Weather Records (1820-1836)

This semester a University of Illinois Department of Atmospheric Science student, Lauren Graham, worked to make available scanned images of the weather records for Fort Armstrong that cover the period 1820 to 1836. Fort Armstrong was located at the present-day Rock Island Arsenal. The original records were maintained and scanned by staff at the Rock Island Arsenal Museum.
These are the oldest official weather records that I have been able to find for Illinois. The records contain daily temperature readings taken at 7 am, 2 pm, and 9 pm, as well as comments on the weather. My favorite is a note in the first month about a “violent hurricane” on July 21 1820 (see image below). I’m sure it was not really a hurricane but either a tornado or severe thunderstorm with high winds.
Here is the press release of the story.
Here is the Fort Armstrong page containing the images and preliminary analysis.
The plans are to introduce more analysis of these data over the summer.

Fort Armstrong, July 1820. Note the comment on July 21 about the “violent hurricane”. Click to enlarge.

Soil Moisture in Illinois

Observed soil moisture data are collected at 19 sites in Illinois by the Illinois State Water Survey’s Water and Atmospheric Monitoring program. The soil moisture is measured at 5 cm (2 inches), 10 cm (4 inches), 20 cm (8 inches), and 50 cm (20 inches). All amounts are reported as the fraction of water by volume of the soil. For example, a value of 0.35 means that 35% of the soil is occupied by water.
Silty clay loam soils, common in Illinois, are considered saturated at values of 0.45 to 0.50. Field capacity is in the neighborhood of 0.35. Values below about 0.20 would be at the permanent wilting point. As the name implies, that is the level where plants wilt and do not recover. Plant roots are unable to recover any water below this level because it is tightly bound to the soil particles. Of course, soil moisture is very dynamic with layers drying or wetting at different rates so it would take low levels of soil moisture at all layers in the root zone to kill a plant.
In general, soil moisture is highest in spring and slowly declines in the summer months because of the heavy demands from evaporation and from transpiration of growing vegetation. In the fall, cooler temperatures and the end of the growing season allow soils to recover quickly.
The map below shows the May 14, 2012, soil moisture status at 10 cm (4 inches). Values in the 0.2 and 0.3 range are widespread. The noticeable exception is in Mason County where the site is located on a very sandy soil. As a result, the moisture drains right out of the soil after a rainstorm.

World-Class Water Survey Scientist Stan Changnon Passes

Stan Changnon, Illinois State Water Survey Scientist, 1928-2012. While I could find several serious pictures of Stan, this one does a better job of capturing his true spirit. While he was a great scientist, he was also a great “people person” as well – a rarity in the scientific arena.

Stan Changnon, world-class Illinois State Water Survey scientist passed away May 1. From his obituary is a brief summary of his remarkable career. Much of what we understand about the climate of Illinois and the Midwest, and how it impacts society, is because of his work. I will highlight some of his scientific contributions in coming weeks.
Furthermore, the stories are coming in from fellow scientists whose careers were touched by his guidance and wisdom. For me personally, I’ve known him my entire professional career and just talked to him last week. I already miss him.

Stan earned his B.S. degree in geography in 1951 and a M.S. degree in geography in 1956 from the University of Illinois, where he later served as Adjunct Professor of Geography and Atmospheric Sciences. He began his professional career as a student at the Illinois State Water Survey in 1951 and retired as Chief of the Water Survey in 1985.
Following his retirement, he was awarded the title of Chief Emeritus and returned to his research as a principal scientist at the Water Survey until 2011. Changnon Climatologist, a scientific consulting firm, was established in 1985. His latest research project, an investigation of Record-Setting Damaging Weather Extremes in 2011, was completed on April 29, 2012.
Stan conceived the national network of regional climate centers and established a center at the Illinois State Water Survey in 1983. Among his many contributions to the atmospheric sciences was his groundbreaking work on how major cities such as Chicago and St. Louis impact the regional weather. His areas of expertise in climate included: climate change, physical and societal impacts of climate, and weather and climate extremes. He served on many national advisory groups, including the Climate Research Committee of the National Academy of Sciences.
He has more than 400 peer-reviewed papers published in scientific journals, over 500 other reports, and has authored more than eight scientific books. His awards for scientific accomplishments include those from the American Meteorological Society, American Association for the Advancement of Science, American Geophysical Union, and the American Water Resources Association. His most recent and prestigious honor was becoming an Honorary Member of the American Meteorological Society in January 2011. Only 102 Honorary Members have been awarded since 1919.

His full obituary can be found at