The amazing formation would be invisible to anyone on the ground and would even be obscure from a regular passenger jet since they can reach up to 75,000ft.
But astronauts captured the astonishing picture from hundreds of miles up as they orbited the globe on the International Space Station.
Anvil clouds are formed mostly from ice and normally form in the upper parts of thunderstorms. They get their shape from the fact that rising warm air in thunderstorms expands and spreads out as the air bumps up against the bottom of the stratosphere.
Streaks of snow are often seen falling out of the edges of anvils. This light snow usually evaporates as it falls through the relatively dry air surrounding the upper part of the thunderstorm.
Images released today showed Tom Marshburn and Christopher Cassidy doing final maintenance work on the exterior of the complex ahead of their departure today.
The four-hour and 54-minute procedure involved rewiring, camera setup, tidying cables and installing handrails and a portable foot restraint to aid future spacewalkers.
The five spacewalks together spanned a total of 30 hours.
The team from the visiting Endeavour shuttle fitted Japan's new outdoor experiments platform with television cameras, completing the final task for the £1.45 billion Kibo complex.
'Congratulations, you guys just completed the ... assembly,' Mission Control radioed once the second camera was secured.
'I can verify from up close it is, indeed, a beautiful laboratory.'
Space shuttle Endeavour's astronauts are inspecting their ship to make sure it's safe for Friday's landing.
The survey of the wings and nose, being conducted Wednesday morning, is standard before a shuttle returns to Earth.
Nasa wants to make sure Endeavour's heat shield was not pierced by micrometeorites or space junk during its two weeks in orbit. The astronauts used a laser-tipped boom to check for damage.
Endeavour and its crew of seven left the international space station Tuesday.
As the inspection was under way, an unmanned Russian vessel carrying several-thousand pounds of supplies docked at the station. Commander Gennady Padalka had to manually guide the craft in because of a problem with its automatic system.
