Kernow Convergence Cross-Country Paragliding
Why fly the Kernow convergence?
- It’s distinctive of Cornwall and the SW due to peninsula convergence.
- It’s a specialization, just like sea thermal flying is.
- It opens up xc potential and distance beyond 10-20km to 50-100km plus.
The facts
1) A sea breeze front is caused by air pressure differences – the warmer/less dense land air rises and draws in the cooler/denser sea air, setting up a convective cell. The strength of a sea breeze depends on (i) the inland surface temperature relative to surface sea temperature and (ii) the degree of instability. It will typically be in a range of 5 and 18 mph.
2) As it comes over land the convective cell can be 50m to 300m in depth. Updrafts at leading edge can push higher than this. As it moves inland it can extend to 2km or more in depth. The line of lift is typically quite narrow; say 100-200m wide. Capping inversions can enhance the convective cell.
3) Cloudbase will be lower on the sea breeze side.
4) Thermals will be organized like this, if the sea breeze is coming from the bottom right. Note the lines of energy with the wind, and along the convergence.
5) Thermals will form and be very active at the boundary of the two air masses on the ground (where the winds meet) – because of the cold air under the warm and because of there being less wind at the boundary.
6) The thermal activity at the boundary is likely to be fairly broken up and need some work to climb in, particulalry in faster sea breeze (where the wedge is more like a blanket).
7) Convergence clouds will be enhanced over higher ground – such as the moorlands.
8) Months May, June, July – expect southerly sea breeze front ~50% of days. In August & September – 30% of days.
9) Generally the updraft created through the leading edge of the front is strong on days of opposing flow (convergence) and weaker when there is same-direction onshore flow (compounding).
10) Weak offshore winds (under 10 mph) > strong sea breeze front, passes over land earlier in day (morning) and push far inland
11) Moderate offshore winds (10-15 mph) > strong sea breeze front, passes over land later in the day (e.g. 3 pm).
12) Weak onshore winds ( less than 7 mph) > sea breeze front can form- but 2-3 hours later than if an offshore wind..
13) Moderate onshore winds (more than 10 mph plus) > suppresses formation of sea breeze front.
14) The sea breeze convergence will have a direction that is the velocity vector sum of the onshore sea breeze front vector and the synoptic wind vector.
The more the prevailing wind tends towards 90 degrees (perpendicular with the sea breeze), the easier it is for the sea breeze to progress inland.
If there is a light 6mph offshore wind, and a 6mph sea breeze the front may be stationary at the coast. The front only moves inland if it can overcome the energy of the prevailing wind. If there is a strong offshore wind and a strong front due to high instability the lift can be very strong and rough.
The image is from 17:00 on a day with strong instability, high temperature and a 15 mph WNW wind.
15) Vortices. These form when there are denser fluids underneath less dense fluids with a shear layer between. These are like billows that propagate away from the front head. This means it will be turbulent on the sea side past the front boundary.
16) As the SBF propagates inland, it may encounter horizontal convective rolls (HCRs) that have formed over the land. These rolls are pairs of tube-like vortices created by surface heating, aligned with the synoptic wind. They tend to develop when there is vertical wind shear. They cause periodic cumuli peaks along the front. These are aligned with the energy lines (cloud streets) that follow the direction of the wind.
17) Double-fronts. Strong convergence can form between two onshore sea breeze fronts – e.g. over Bodmin Moor.
Flying the Kernow Convergence
1) For predicting the right conditions you need info on prevailing wind (and change over course of day), instability, inversion, satellite cloud images, and RASP convergence.
2) Convergence XC will depend on accessing the right hills. One hour drives to Bodmin Moor may be typical.
3) Convergence XC will depend on having good skills in climbing out of small hills/tors with broken fast-drifting thermals. This may need tight 360s, zig-zagging over the hill with a fast-drifting thermal then pushing forward multiple times, not taking risks by pushing out in front if not in a thermal, and sometimes leaving the hill relatively low. The more practice on Carn Brea, Rosewall, Zennor/Trewey/Trendrine & Godrevy the better!
4) The lower wedge of the denser sea breeze is a zone where there is a lot of thermic activity. This means that you could get away at the intersection of the sea breeze convergence and then push forward to the sea breeze lift (e.g. at Carn Brea when the wind is very light). Alternatively you need to climb out somewhere and fly back with the wind to connect with a sea breeze front coming in another direction.
5) The lift line of a sea breeze front can be soared like a ridge.The lift line is narrow (100-200m) – and there may be cloud suck, so flying along the front may involve zig-zagging (e.g. 30 deg) in and out of the lift.
6) Avoid air on the seaward side of convergence. It will be moist, dull air and sinking / turbulent.
7) XCs from Bodmin Moor will need public transport (trains/buses) to try to get back to your car – or using SW Retrieve Telegram group (long shot). This will need figuring out.
Kernow Convergence XCs
Getting there: Poldhu Downs car park: 1 hour 10 min from Hayle. half hour walk in.
Getting there: Bowithick village: 1 hour 10 min from Hayle. 10-15 min walk..
Getting there: Caradon Hill Transmitter: 1 hour 15 min from Hayle. No walking.
Getting there: North Hill carpark: 1 hour 10 min from Hayle. 15 min walk up hill.
Getting there: Helman Tor: 45 min from Hayle. No walking.
(Also Trewey/Trendrine hills)
Other useful links
Understanding Sea Breeze Convergence – Cross Country Magazine
How to recognize and fly convergence – G Dale
Flying the Sea Breeze Front – Greg Hamerton Youtube Video
Glider flying along convergence line – YouTube
About the Author
Mark Ashton Smith What’s national standard for paragliding in Cornwall - among the best you can find in the country? (1) the coastline 🧗🏼♀️ - the most beautiful in the country. We can enjoy it, explore it, and get good at coastal soaring 🏆 (2) the views 👀from up high - all coastlines of the peninsula that everyone comes to visit all in one panorama - absolutely stunning 🏆 (3) technical tor & small hill, inverted, broken-up, and low base flying 💥- really sharpens XC skills - none of this lobbing into house thermals and climbing to 6-7 grand off the bat. If you lose concentration you’re on the ground. If you can learn to fly XC well in gnarly Cornwall you can fly well anywhere in the UK. 🏆(4) the convergence 🌥🌥🌥 - it’s the best in the UK and if we can fly it, it opens up 150km plus flights and even learning to soar sea breezes gets us in league with that lot around Brighton. 🏆 (5) We got instant access to lots of ace coastal sites/beaches to train at within a short drive which gives us more air time, ground handling skills, and wagga skills (call out to Dunc)🏆,and (6) our sites aren’t busy!! You’ll be lucky to find more than 2 people flying at Carn Brea on a perfect day. In Bodmin moor you’ll be with your mate and that’s it. No crowds. 🏆👌Happy to be in one of the best flying areas in the country - just important not to get pulled into the league numbers games which suits other areas but not ours. Gavin McClurg made the same point. Distance is great but there’s loads of other ways to have top flights. Focus on what’s the very best in your home turf! 🏴☠️
