The Invisible Variable behind Tornadic Events? Sensing Water Vapor from Space

In May 2013, two deadly tornadoes struck near Oklahoma City within a two week time span. The 2013 Moore tornado was an EF5 tornado that touched down near Moore, Oklahoma at 2:56pm on May 20, 2013 injuring 377 and killing 24 people. On May 31st, the widest tornado in history struck at 6:03 pm near El Reno, Oklahoma, another suburb of Oklahoma City injuring 151 people and killing 8, including experienced storm chasers. Thousands of residents in Oklahoma City decided to outrun the second storm, only to cause a freeway traffic jam and put themselves at great risk. With these tragic extreme weather events as case studies. We will illustrate the important role that water vapor plays in the formation and intensity of severe storms. Despite the recognized importance of water vapor in the “triggering” of rapid convection in the Great Plains, the ability to measure the vertical distribution of water vapor is very limited. Unlike clouds, water vapor is invisible to both the human eye and to Doppler radar. In situ measurements at the surface from the Oklahoma Mesonet provide important clues to the horizontal distribution of water vapor but give no information on the vertical extent. The problem is that weather balloons give vertical profiles of relative humidity but only at 0 and 12 UTC, which for Oklahoma under DST is 7 am and 7 pm, either too early or too late to be directly useful in characterizing the atmospheric change for the Oklahoma tornadoes. Between the time that forecast warnings are available from NWP model predictions, based on the weather balloon input data after 0 UTC, and the time that rotating clouds can be detected by Doppler radar, there are two important satellite overpasses at about 10:30am and 1:30 pm. Data from the European METOP satellite and the U.S. Suomi NPP satellite, respectively can help fill in the gap. Each of these satellites hosts a new type of infrared sensor that can probe the vertical distribution of water vapor. This presentation will illustrate the remote sensing capability of these new satellite data and show what new information they can provide to future predict tornado outbreaks anywhere in the United States. Validation data is presented from a research site in north central Oklahoma operated by the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program and NASA aircraft operating nearby. With the use of satellite data, forecasters will be able to better predict natural disasters and therefore give more timely and accurate warnings.