Meteorologists know that severe hail (greater than one inch in diameter) typically forms in rotating supercells with strong updrafts. However, “clear ideas on how they form and how to predict these events in advance have proven elusive,” says the National Science Foundation (NSF), a major sponsor of the OU research.
Scientists working on the Severe Hail Analysis, Representation and Prediction (SHARP) project are aiming to improve forecasting by fine-tuning the resolution of a forecast model. Currently the highest-resolution models the National Weather Service has is with a grid spacing of every three kilometers. But by using STAMPEDE, one of the most powerful supercomputers in the world, grid spacing can be reduced to 500 meters.
“This lets us simulate the storms with a lot higher accuracy,” says Nathan Snook, an OU research scientist.
The NSF report states “there’s a major effort underway to move to a ‘warning on forecast’ paradigm — that is, to use computer model-based, short-term forecasts to predict what will happen over the next several hours and use those predictions to warn the public, as opposed to warning only when storms form and are observed.”
An area known as the “hail belt” is the major focus area for the SHARP project. That is because most severe hail events in the U.S. occur in the Central Plains and west across the high desert to the Rocky Mountains. And the hail can be impressive.
On July 11, 1990, one of the costliest hail storms ever to hit the U.S. struck northwest of Denver. A thunderstorm that formed near Rocky Mountain National Park drifted over the plains, pelting the landscape with golf-ball-sized hail in a swath up to 10 miles wide.
Tens of thousands of cars were peppered, many of them totaled, thousands of homes sustained major damage, trees were stripped of foliage and, to add insult to injury, ice-clogged storm drains and streets overflowed, flooding homes.
It’s hard to believe, but the largest hail stone ever recorded in the U.S. was 7.9 inches in diameter. On July 23, 2010, in Vivian, S.D., Lee Scott collected the stone, which weighed in at 1.94 pounds, also a record. He had originally planned to toss it in a blender and make daiquiris. However, after realizing that the frozen globule might be special, he turned it over to the National Weather Service for official measurements.
Hail has also been known to pile up in great depths. Up to four feet of hail accumulated in one city block in downtown Denver on July 5, 2015, when a thunderstorm stalled over the area and continually hailed for an hour and half. When it was over, tractors filled up more than 30 dump trucks to haul it away.
For people living in the “hail belt” from Texas to North Dakota, the improved forecasts could have profound implications. For example, a two-hour warning could save your automobile from destruction by giving enough of a heads-up to put it in the garage.
“This has the potential to change the way people look at severe weather predictions,” Snook says. “Five or 10 years down the road, when we have a system that can tell you that there’s a severe hail storm coming hours in advance, and to be able to trust that — it will change how we see severe weather. Instead of running for shelter, you’ll know there’s a storm coming and can schedule your afternoon.”