On Sunday, May 18, 2014, the Basehunters storm-chasing team from Norman, Oklahoma, filmed a supercell thunderstorm taking shape over the plains of northeast Wyoming. Shot as they drove from Wright towards Newcastle, their time-lapse showed the storm's rotating updraft stacking cloud upon cloud like a spinning layer cake. Within a day it was being shared by NPR, Slate's Bad Astronomy blog and news sites around the world.
The Basehunters time-lapse from Wright to Newcastle
Wright and Newcastle sit in the grassland and sagebrush country of northeast Wyoming, between the Powder River Basin and the Black Hills. The open horizon is perfect for storm photography: nothing blocks the view of a cloud base, and a storm can be followed for miles.
The Basehunters crew pointed their cameras at the storm as it organised and moved towards them, then kept shooting as they repositioned. That is why the footage jumped in places: the team was driving to stay ahead of it. The crew also tweeted still photographs of the storm's banded, rotating structure towering over the prairie, and NPR ran one with its story the next day.
What is a supercell?
The National Weather Service describes the supercell as the least common type of thunderstorm and the one most likely to produce severe weather: damaging winds, very large hail and tornadoes. What sets it apart is a deep, persistent rotating updraft called a mesocyclone.
The key ingredient is wind shear: winds that strengthen and change direction with height, from the surface to around 20,000 feet. Shear sets the rising air spinning and tilts the storm, which keeps its updraft and downdraft apart. Because the storm does not choke on its own rain-cooled air, a supercell can last for hours.
Why this storm looked so sculpted
Meteorologists describe supercells in three broad types: classic, high-precipitation (HP) and low-precipitation (LP). The Wyoming storm was an LP supercell, a type that forms in dry air with strong winds aloft. With little rain falling to curtain the view, the whole rotating updraft stood exposed, showing the striations that give these storms their "mothership" look. LP supercells are most common in the drier western Plains, including the Texas and Oklahoma panhandles, and the rain they lack is often replaced by very large hail.
The Wyoming storm put on a spectacular show without producing a tornado: NOAA's Storm Prediction Center logged no tornado from it, while the only two tornadoes reported that Sunday were in Nebraska and Montana. That is typical. Most supercells never produce one, which is why forecasters watch radar signatures of rotation so closely.
How time-lapse reveals storm structure
A supercell evolves too slowly for the eye to see its rotation in real time but fast enough to change shape within minutes. Time-lapse photography solves that: by shooting a frame every few seconds and playing them back at video speed, a camera compresses an hour into a minute, and the slow turning of the mesocyclone suddenly becomes obvious.
Storm chasers who do this work follow forecasts, radar and road networks closely and keep an escape route open. If you see a storm like this from home, follow local National Weather Service warnings and take shelter when one is issued.
Related reading
- The May 2014 Watford City Tornado on Video
- Beautiful, strange and rare cloud formations
- Sun Halos over Finland: Understanding Pauli Hänninen’s Photographs
- Denton’s April 3, 2014 Hailstorm: Photographs, Videos and the Weather Record
- New York’s January 2014 Snowstorm in Time-Lapse
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