Ice

Hail the size of grapefruit shattered car windows in Johnson City, Texas. In June, 2024, a storm chaser found a hailstone almost as big as a pineapple. Even larger hailstones have been documented in South Dakota, Kansas and Nebraska. Hail has damaged airplanes and even crashed through the roofs of houses. How do hailstones get so large, and are hailstorms getting worse? As an atmospheric scientist, I study and teach about extreme weather and its risks. Here’s how hail forms, how hailstorms may be changing, and some tips for staying safe. How does hail get so big? Hail begins as tiny crystals of ice that are swept into a thunderstorm’s updraft. As these ice embryos collide with supercooled water – liquid water that has a temperature below freezing – the water freezes around each embryo, causing the embryo to grow. A hailstone cut in half, which reveals layers of clear and cloudy ice formed as the hailstone journe...

One of the most robust measures of Earth’s changing climate is that winter is warming more quickly than other seasons. The cascade of changes it brings, including ice storms and rain in regions that were once reliably below freezing, are symptoms of what I call “warming winter syndrome.” Wintertime warming represents the global accumulation of heat. During winter, direct heat from the Sun is weak, but storms and shifts in the jet stream bring warm air up from more southern latitudes into the northern U.S. and Canada. As global temperatures and the oceans warm, that stored heat has an influence on both temperature and precipitation. The U.S. has been feeling this warming in the winter of 2023-24, the warmest on record for the Lower 48 states. Snowfall has been below average in much of the country. On the Great Lakes, the ice cover has been at record lows. Late February saw a wave of summerlike temperatures spread up into the central and eastern U.S., along wi...

An avalanche swept up skiers at Lake Tahoe’s largest ski resort on Jan. 10, 2024, as a 150-foot-wide sheet of snow slid down a mountain slope into a pile 10 feet deep. One person died in the avalanche and three others were rescued, according to the Placer County, California, Sheriff’s Office. The slide happened in steep terrain near the KT-22 chairlift, which had just opened for the season that morning. A second unplanned avalanche hit the same ski resort the next day, but no one was injured. Avalanche deaths are rare inbounds at ski resorts like Palisades Tahoe, but the risk rises in the backcountry – 30 backcountry avalanche deaths were reported in the U.S. during the 2022-2023 season. Nathalie Vriend, a skier and physicist at the University of Colorado Boulder who studies avalanches, explains what happens in an avalanche and techniques for surviving one. What causes avalanches? The behavior of an avalanche depends on the structure of the snowpack, but that...

In August 2023, residents of Juneau, Alaska, watched as the Mendenhall River swelled to historic levels in a matter of hours. The rushing water undercut the riverbank and swallowed whole stands of trees and multiple buildings. The source for the flood was not heavy rainfall – it was a small glacial lake located in a side valley next to the Mendenhall Glacier. Glacier-dammed lakes like this are abundant in Alaska. They form when a side valley loses its ice faster than the main valley, leaving an ice-free basin that can fill with water. These lakes may remain stable for years, but often they reach a tipping point, when high water pressure opens a channel underneath the glacier. The rapid and catastrophic drainage of lake water that follows is called a glacial lake outburst flood, or GLOF for short. The flood waters race downstream over hours or days and often hit unexpectedly. Suicide Basin, a glacier-dammed lake, has flooded the Mendenhall River...

I’m striding along the steep bank of a raging white-water torrent, and even though the canyon is only about the width of a highway, the river’s flow is greater than that of London’s Thames. The deafening roar and rumble of the cascading water is incredible – a humbling reminder of the raw power of nature. As I round a corner, I am awestruck at a completely surreal sight: A gaping fissure has opened in the riverbed, and it is swallowing the water in a massive whirlpool, sending up huge spumes of spray. This might sound like a computer-generated scene from a blockbuster action movie – but it’s real. Alun Hubbard stands beside a moulin forming in a meltwater stream on the Greenland ice sheet. Courtesy of Alun Hubbard A moulin is forming right in front of me on the Greenland ice sheet. Only this really shouldn’t be happening here – current scientific unders...