WEEK 27: OKLAHOMA
“O-O-Oklahoma, Where the (Arctic) Wind Comes Sweepin’ Down the Plain”
By Dr. Steven Cavallo, Assistant Professor, School of Meteorology, University of Oklahoma, Norman, Oklahoma
Oklahoma, where the wind comes sweepin’ down the plain,
And the wavin’ wheat can sure smell sweet
When the wind comes right behind the rain…
— Lyrics from the Rodgers & Hammerstein musical Oklahoma!
May 10, 2010 is a date that even to this day still reverberates in the minds of Oklahoma residents. It’s not unusual for tornadoes to occur in Oklahoma in May. In fact, more tornadoes then than at any other point during the year — with 22.7 tornadoes occurring on average. However, that particular May in 2010 brought a particularly extreme outbreak of severe weather that included dozens of tornadoes being reported across the state in one day — an extremely unusual weather occurrence, even in tornado-prone Oklahoma.
At the University of Oklahoma, atmospheric scientists in the School of Meteorology’s Arctic and Antarctic Research Group (AAARG) are studying severe weather patterns — like those that led to the May 10th event — in hopes of predicting them much further in advance, allowing people more time to prepare. Right now, a severe thunderstorm over a large region can only be predicted one to three days in advance, while a site-specific thunderstorm can only be predicted an hour in advance.
To better understand and predict extreme weather patterns, AAARG has started to look to the Arctic for answers, and they’ve found that the polar vortex plays a role in these. When the polar vortex is strong, Arctic air circulates along more predictable routes around the North Pole. However, when the polar vortex is weakened — a side-effect of climate change — Arctic air can break free from the north and find its way south, even down to Oklahoma. AAARG scientists are studying the links between weak polar vortices and this cold Arctic air, which we scientists refer to as the tropopause polar vortices (TPVs).
TPVs may sound complex, but they are simply isolated pockets of cold air that form at a high elevation in the Arctic’s atmosphere. These TPVs spend most of their lifetime in the Arctic, but as the result of a weak polar vortex, the jet stream can sweep them down into lower latitudes. This not only makes Oklahoma residents chilly, but brings extreme weather events like tornadoes and thundersnow.
TPVs are connected to many extreme events, including winter storms (for example, Nor’easters) and extreme cold air outbreaks (like the polar vortex in January 2014). As the climate changes, and as these sorts of extreme weather events occur across the United States, we in Oklahoma are working to better understand the connection.
How often do TPVs pass over Oklahoma?
TPVs pass overhead frequently near where they originate in the Arctic . In parts of northern Canada, there is a 35–40% chance they will pass on any given day. Over Oklahoma, this probability is well under one percent. This would translate into about one or two TPVs per year that pass directly over Oklahoma. However, TPVs only need to pass by our region here in Oklahoma for it to impact us. With that consideration, even a few TPVs per year will likely have an impact on Oklahoma weather.
You may be asking yourself why you should care about TPVs if they are so rare. One thing to consider is that extreme severe weather outbreaks are also infrequent. Many of my colleagues and I have found TPVs are a key ingredient in determining when severe weather will occur.
What can we do from Oklahoma to learn more about how the Arctic influences severe weather and improve weather prediction?
Our research shows that weather models are consistently predicting weaker TPVs than those that are observed. This means forecasters are likely underestimating severe weather outbreaks. In order to build more accurate weather models, we need to continue studying TPVs.
Instead of waiting around for that infrequent TPV to pass through Oklahoma, our scientists have teamed up with National Oceanic and Atmospheric Administration (NOAA) scientists to take measurements from an observing station located at the summit of the Greenland ice sheet — conveniently called Summit Station — where TPVs pass by much more frequently than they do in Oklahoma.
There are many instruments to measure atmospheric properties near TPVs at Summit Station. Our research includes using a ground-based detection system called lidar, which uses lasers pointed upward to study the upper layers of the atmosphere. Weather balloons are also launched at least twice per day to gather data from the ground up to 15 miles above Earth’s surface.
Ultimately, we hope to gather enough data from the TPVs that pass over Greenland to incorporate that information into numerical weather models to improve predictions of severe weather. Letting people know about a risk further in advance can help residents and emergency managers prepare and plan before a storm is already imminent.
National Severe Storms Laboratory In Oklahoma is one of the many scientists from the state carrying out weather research in the Arctic (Photo credit Dr. David Turner).
The Greenland station is supported by the National Science Foundation (NSF), NOAA, and the Department of Energy (DOE). However, the scientists involved in this research are based in an Oklahoma building called the National Weather Center (NWC). The NWC is the largest research center of its kind in the nation, and it is here that federal entities, state organizations, and the University of Oklahoma School of Meteorology work together to improve understanding of events occurring in Earth’s atmosphere.
Having everyone under one roof allows scientists, professors, students, and forecasters to more easily combine notes and collaborate with each other to foster growth in the science. As our scientists here in Oklahoma learn more about the Arctic’s TPVs, the NWC is the ideal facility to pass this knowledge along to weather forecasters, who can broadcast the information to affected communities. In this crucial way, Oklahoma is doing its part in the Arctic and helping keep communities a bit safer on the ground when extreme weather events — from tornadoes to thundersnow and thundersleet— strike.
About the Author:
Dr. Steven Cavallo is an Assistant Professor at the University of Oklahoma’s School of Meteorology. He developed and leads the Arctic and Antarctic Research Group in the National Weather Center, located on campus in Norman, Oklahoma. He holds a Ph.D. from the University of Washington in Atmospheric Sciences that was received in 2009. Before arriving at the University of Oklahoma in 2011, he completed a Postdoctoral Fellowship in Polar Regions Research awarded by the National Science Foundation and carried out with scientists at the National Center for Atmospheric Research in Boulder, Colorado. To learn more about him or his research, click here or email him at cavallo@ou.edu.
Special Thanks to:
Dr. David Turner of NOAA: Dr. Turner is the Co-Principal Investigator of the National Science Foundation Integrated Characterization of Energy, Clouds, Atmospheric State, and Precipitation over Summit (ICECAPS) Observatory at Summit, Greenland.
Dan Whittaker, photographer: Mr. Whittaker is an award-winning photojournalist, videographer, and storm chaser who uses his work to promote land conservation and awareness of nature. See more of his stunning photos here: http://www.lightexplored.com.
