"We measured twice the forecast speed" implies that the previous forecast wasn't close to the extreme end, so it's not true that they only ever publish extreme

"We measured twice the forecast speed" implies that the previous forecast wasn't close to the extreme end, so it's not true that they only ever publish extreme numbers. I wonder what the extreme end actually is. The glacier (the part on land) is sliding down into the sea at a speed of half a centimeter per minute now, and the main factor holding the speed down is disappearing. How fast can ice slide?