New study links cloud top appearance to lightning in a snowstorm.
Weather Channel meteorologist Jim Cantore was reporting on the blizzard when a sudden purple flash illuminated the skies. “hello! We got it baby!” He yelled, repeatedly leaping in the atmosphere. The”it” was thundersnow — that the comparatively rare, sometimes unnerving, sometimes thrilling overall look of lightning and thunder during a snowstorm.
The scarcity of thundersnow events, while probably compounding the joy of weather lovers who experience themhas also meant that scientists don’t understand thundersnow as well as traditional summer thunderstorms. Research was limited by biased or small datasets, in addition to less pressure to forecast thundersnow.
But now researchers have a new tool at their disposal: A newly launched satellite instrument, called the Geostationary Lightning Mapper, or GLM, may gather images of lightning flashes night and day, winter and summer, over almost an entire hemisphere. And scientists are tapping into this wealth of new information to unlock more of thundersnow’s secrets.
A summer thunderstorm generally develops when warm humid atmosphere near the Earth’s surface rises and condenses into towering thunderclouds. Inside the cloud, water condenses and freezes into small particles that swirl around, colliding and separating opposite electrical charges. Negative charges build up in 1 portion of this cloud, then — zap — jump to a positively charged part of this cloud or the floor for a bolt of lightning.
The atmosphere and swirling ice cubes are characteristics of thundersnow too, but it is harder for those conditions to grow in winter, once the earth is colder. The updrafts associated with thundersnow are generally weaker and, except in the case of lake-effect snow, don’t usually begin from the floor. Most often, it takes the electric charges longer to build up in the clouds and the bolts of lightning are more spread out in time.
Sebastian Harkema, an atmospheric science student in the University of Alabama in Huntsville, worked with scientists at NASA Marshall Space Flight Center to analyze GLM information from 2018 to 2020 and identify tens of thousands of instances of thundersnow over the contiguous United States of America. In contrast, there were likely over a million regular thunderstorm lightning flashes during this exact same time. The researchers found that thundersnow flashes on ordinary were bigger and longer-lasting than ordinary rainfall-associated lightning. They also found that thundersnow happens more frequently in storms that dump a lot of snow, however, that the areas inside the storm that are undergoing thundersnow are in the time spatially separated from the regions with the maximum snowfall prices.
In new research that’s not yet printed, Harkema and his mentors linked the changing look of cloud tops in satellite pictures over the course of two hours into the greatest initiation of a thundersnow flash. They found that the cloud tops undergo a comparable, but less conspicuous, change in look as cloud tops before lightning appears during a standard thunderstorm. The change in the satellite pictures can be connected to the physical changes in the cloud once the top becomes icy and the ice cubes grow smaller over time, likely because they’re colliding and breaking apart. Harkema presented the study in the virtual meeting of the American Meteorological Society last week.
Thundersnow is normally less of a direct threat to people than thunderstorm lightning, both because it is rarer and it occurs during chilly weather that tends to induce people inside. But the studies from Harkema and others that have found connections between thundersnow and heavy snowfall indicate a better understanding of thundersnow could also help researchers better forecast snowfall rates and levels. This in turn could indicate the public receives a more accurate warning of adverse winter weather with more time to prepare.
“There’s a pure science aspect to this work, about knowing the microphysics within a cloud, but there is also the applied aspect of enhancing the prediction. It’s ringing all the bells,” explained Patrick Market, a meteorologist at the University of Missouri at Columbia that has analyzed thundersnow but was not involved in the new research.
“The Geostationary Lightning Mapper is an excellent instrument to be able to really capture all the lightning that occurs in these more infrequent situations like thundersnow,” explained Eric Bruning, a meteorologist at Texas Tech University. “It’s always beneficial to have these studies which are taking a look at these less researched portions of the atmosphere”
Harkema said he has been excited by the relatively uncharted lands of his job. Although some colleagues joke he could be gunning for the title of”Dr. Thundersnow,” he has yet to watch the weather phenomenon in real life. “That’s something that is definitely on my own bucket list,” he explained.