Tuesday's tornado outbreak: 3 things to watch for
It's clear that there is going to be a widespread outbreak of severe thunderstorms on Tuesday, with the greatest threat for "giant hail," damaging winds and violent tornadoes extending from Nebraska southward into north Texas.
What is unclear, though, are key details of how the outbreak will unfold, which will affect how well people can respond to the threat and protect themselves.
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Here are three things to watch for as the outbreak unfolds on Tuesday afternoon.
1. Where will supercell thunderstorms develop?
The Storm Prediction Center (SPC) in Norman, Oklahoma, is anticipating the development of supercell thunderstorms on Tuesday afternoon into the evening, and possibly into the overnight hours, across the central U.S.
Supercells are the most fearsome breed of thunderstorms, containing rotating updrafts that allow them to persist for long periods of time while manufacturing large, damaging hail, strong winds and tornadoes.
Forecast certainty and clarity often increase as events get closer -- but not always.
Such supercells depend on sufficient amounts of instability, atmospheric wind shear and a trigger to set them off, like a match thrown on a pool of gasoline.
There is no shortage of triggers on Tuesday, but it's not clear yet how each wave of storms will develop and which region or regions will be most affected.
In a forecast discussion on Tuesday morning, the SPC said a "substantial severe weather event is expected today and tonight."
Forecasters at SPC, which is a unit of the National Weather Service, are anticipating up to three rounds of thunderstorms through Tuesday evening, with the greatest threat for severe weather lying along a warm front near the border between Kansas and Nebraska. Such fronts can enhance low level wind shear, elevating the threat for tornadoes.
The presence of several fronts and other weather features are complicating the forecast, though.
"Specifics are still rather nebulous," SPC forecasters wrote on Tuesday. "Forecast certainty and clarity often increase as events get closer -- but not always."
The main trigger for the storms this afternoon will be a pinwheeling area of low pressure aloft that is rotating out of the Southwest, with an upper level area of low pressure expected to develop across northwestern Kansas and southwestern Nebraska overnight. This low pressure area will force the air to rise across the central Plains states, leading to powerful thunderstorms.
2. Is this mostly a hail threat, or multiple tornadoes too?
The SPC has issued a moderate risk outlook for severe thunderstorms today from southern Nebraska into north Texas, mainly because of a high likelihood of widespread, damaging hail. Forecasters mentioned the potential for 3-inch diameter hail or greater in some storms, which can cause significant damage to crops, cars and even homes.
Just ask residents of the Dallas-Fort Worth metroplex, who have seen at least two hailstorms this spring rack up a tab of more than $1 billion.
3. Will the advanced notice help?
Forecasters have warned people since April 21 that Tuesday would be a risky day for severe weather, hoping that this message would resonate with everyone from homeowners needing to clean out a storm shelter to emergency managers who need to test tornado sirens.
However, social science data suggests that longer lead times, at least when it comes to tornado warnings, can be counterproductive.
When people have an hour of advanced notice for an approaching tornado they can often take actions that put them in more danger, like fleeing their homes rather than seeking shelter within them.
A 2011 study found that shorter warning times of about 15 minutes (the national average is 13 minutes) can prompt more effective actions.
In 2013, a TV meteorologist in Oklahoma City told residents in the path of an approaching tornado, which was about an hour away from the city, to get in their cars and flee to safer ground, which contributed to a massive traffic jam that put people in more danger.
Five motorists, including three experienced tornado chasers, Tim Samaras and his son Paul as well as chase partner Carl Young, perished when a multi-vortex tornado tossed their vehicles off a highway. That fierce twister turned out to be the widest ever recorded, at 2.6 miles in diameter.
Tornado warning lead times have improved in recent years due to advances in Doppler radar technology. At the same time, meteorologists have improved their ability to highlight severe weather threats several days in advance as computer model projections have become more precise.
What's unclear, though, is how effective such advanced notification is, given how people tend to prioritize near-term threats over distant ones. The National Weather Service is working with social scientists to improve its messaging to ensure that its forecasts, including severe thunderstorm outlooks, are more widely understood and acted upon.
One downside to outlooks like this is it can heighten the number of storm chasers on area roadways, creating a higher chance for what is known in the business as "chaser convergence."
The 2013 tornado season saw the first-ever tornado chaser fatalities, but experienced chasers don't think it will be the last, given the high demand for thrilling YouTube tornado footage and the tendency for many chasers to put themselves in harm's way.
Andrew Freedman is Mashable's Senior Editor for Science and Special Projects. Prior to working at Mashable, Freedman was a Senior Science writer for Climate Central. He has also worked as a reporter for Congressional Quarterly and Greenwire/E&E Daily. His writing has also appeared in the Washington Post, online at The Weather Channel, and washingtonpost.com, where he wrote a weekly climate science column for the "Capital Weather Gang" blog. He has provided commentary on climate science and policy for Sky News, CBC Radio, NPR, Al Jazeera, Sirius XM Radio, PBS NewsHour, and other national and international outlets. He holds a Masters in Climate and Society from Columbia University, and a Masters in Law and Diplomacy from The Fletcher School at Tufts University.
