I enjoyed this one! The Helm wave is maybe a bit atypical in that it requires particular contrasting met conditions either side of the ridge and turbulence is probably part and parcel of it. From my hang gliding days I know that the best wave formations occur with a combination of stable high pressure and a temperature inversion, which traps the airflow so that it effectively bounces off the ridge, onto the inversion and back down again. The source of the wave can be many, many miles upwind and the lift it affords is amplified with successive wave sequences, each often marked by a bar cloud where moisture in the rising air condenses. While turbulence is not unknown, once you're flying in the wave itself it's usually very smooth. I once stood at the top of Hartside Pass on an otherwise calm day and was almost blown off my feet as the air raced up across the Durham moors and down into the Eden Valley. Tales of the Helm are legend: supposedly a fireman on the famous Settle-Carlisle railway had the coal blown off his shovel is one such that I recall.
Thanks, glad you liked the post. And yes the Helm Bar is sometimes described as a rotor cloud, which is something to avoid in light aircraft/gliders. I’ve seen that wind speeds can reach Force 9 on top of the ridge when the Helm blow. Fascinating to hear about flying in more typical wave, and I vaguely remember reading about a hang glider pilot tackling the Helm (maybe Bob Calvert) which must have been quite a flight!
I enjoyed this one! The Helm wave is maybe a bit atypical in that it requires particular contrasting met conditions either side of the ridge and turbulence is probably part and parcel of it. From my hang gliding days I know that the best wave formations occur with a combination of stable high pressure and a temperature inversion, which traps the airflow so that it effectively bounces off the ridge, onto the inversion and back down again. The source of the wave can be many, many miles upwind and the lift it affords is amplified with successive wave sequences, each often marked by a bar cloud where moisture in the rising air condenses. While turbulence is not unknown, once you're flying in the wave itself it's usually very smooth. I once stood at the top of Hartside Pass on an otherwise calm day and was almost blown off my feet as the air raced up across the Durham moors and down into the Eden Valley. Tales of the Helm are legend: supposedly a fireman on the famous Settle-Carlisle railway had the coal blown off his shovel is one such that I recall.
Thanks, glad you liked the post. And yes the Helm Bar is sometimes described as a rotor cloud, which is something to avoid in light aircraft/gliders. I’ve seen that wind speeds can reach Force 9 on top of the ridge when the Helm blow. Fascinating to hear about flying in more typical wave, and I vaguely remember reading about a hang glider pilot tackling the Helm (maybe Bob Calvert) which must have been quite a flight!