NWC REU 2015
May 26 - July 31



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The Effects of Antecedent Soil Moisture Anomalies on Tornadic Activity in the United States

Ryann Wakefield, Esther Mullins, Derek Rosendahl, and Harold Brooks


What is already known:

  • Seasonal forecasting of severe weather, especially tornadoes could help increase preparedness, and awareness in particularly vulnerable regions during a given year.
  • Previous research has shown a link between soil moisture and convection, but relatively little work has been done to examine the relationship between tornado activity and antecedent soil moisture in a large portion of the United States.

What this study adds:

  • Multiple experiments examining 6 month antecedent soil moisture averages demonstrated a relationship between soil moisture and tornado activity in some of the regions examined.
  • Regions with a relationship between soil moisture and tornado activity had different correlations at different times of the year, motivating future research to understand the physical mechanisms causing such relationships.
  • The Climate Prediction Center (CPC) modelled soil moisture dataset used for this analysis was compared against observed values from the Oklahoma Mesonet to demonstrate that the CPC dataset reflects reality well.


Recently there has been increased interest in the ability to forecast severe weather events on a seasonal scale. Be- ing able to forecast events such as the April 2011 outbreak could have beneficial impacts such as increased prepar- edness at the Federal and local level as well as greater public awareness. To better forecast tornadoes on a sea- sonal scale, we must first look at the underlying factors that influence the inter-annual variability of both tornado loca- tions and intensity. Soil moisture has been shown, on regional scales, to have an effect on moisture within the bound- ary layer, and therefore, the potential for deep convection. Previous studies have examined relationships between factors related to soil moisture such as precipitation and evapotranspiration and their effects on tornado climatology at the local and regional scale. This study examined the relationship between antecedent soil moisture and tornado activity in five regions within the United States east of the Rocky Mountains, using two approaches. The first ap- proach used fall and winter soil moisture anomalies as a predictor for spring tornado activity while the second looked at the six months preceding each month in the year. In addition, we also assessed the reliability of our modeled soil moisture dataset by comparing it to the high-resolution Oklahoma Mesonet observational network.

Full Paper [PDF]