The Soarable Tops Switch: How to Read and Use the Air School Paragliding Forecast
The Air School automated paragliding forecast has become a valuable tool for pilots across Cape Town and the Western Cape. It highlights likely flyable sites, saves time, and helps pilots spot opportunities they may otherwise miss.
This updated post explains the new shift to Soarable Thermal Tops, clarifies how to interpret the values, and gives a detailed walkthrough of how to use the forecast safely and effectively.
If you're new to the tool — or recommending it to someone else — this guide will give you everything needed to understand it properly.
Why I Switched to Soarable Thermal Tops 🧐
For years, the forecast displayed Boundary Layer Tops (BL tops) for each site. There were two main reasons for this:
1. BL tops are a good indicator of inversion height
Inversion altitude is an important safety consideration for paragliding in the Western Cape. BL tops are not a perfect match for inversion height, but they are often a good proxy.
2. BL tops reflect the RASP model's calculation height
The Boundary Layer is a core part of RASP's predictive engine. Knowing this value helps understand model quirks and shortfalls — for example, when a wind gradient extends above the BL top on a prefrontal day and RASP thinks it's still "good."
However, over time, pilot feedback became both consistent and reasonable:
"Can you please show the soarable height so we can quickly understand how high we're actually likely to climb on the day?"
This feedback made sense — because soarable tops are simply more practical for real flying decisions. They answer the direct and functional question pilots care about: How high will thermals likely take me at this site around that time?
What Made the Change Possible Now?
My original hesitation to switch from BL tops to soarable tops was that I didn't want to lose the insight BL tops provided regarding inversion height and possible model limitations.
Two things made the change possible:
- The regional Boundary Layer Tops are available. These regional BL values (Cape Town International, Porterville, Sedgefield) continue to give an excellent sense of inversion height — preserving the key safety info that BL tops provide.
- Per-site soarable tops give the intuitive, practical numbers pilots have been asking for. Pilots get a clear picture of how high they are likely to climb, while still having the deeper BL-structure information available elsewhere.
The new combination (regional BL + site-specific soarable) is the best blend of safety and practicality.
This change was made because pilots asked for it, and because it genuinely improves usability, clarity, and decision-making for the whole community.
What Is the Soarable Thermal Top? 📈
The soarable top (hcrit) is the altitude at which a thermal's upward velocity drops to roughly 1 m/s — similar to a paraglider's sink rate. Below this height, you climb; above it, you no longer gain altitude.
This makes soarable tops the ideal metric for the forecast table because they represent the realistic thermal ceiling for paragliders.
Why Boundary Layer Tops Still Matter (Regionally) 🌐
Boundary Layer Tops remain extremely useful as a proxy for inversion height. This is important for safety.
That's why regional BL values are still included for the key reference points:
- Cape Town International
- Porterville
- Sedgefield
These tend to match observed inversion behaviour surprisingly well, especially inland.
How to Read and Use the Forecast 🤓
Each site displays:
- Soarable Thermal Top (m ASL)
- Surface Wind Speed (kph)
- Surface Wind Direction
Example: "1350m | 12SE" → Soarable top 1350m, surface wind 12 kph from the southeast.
If a site appears in the table, it passed checks for a range of variables — such as fog, wind speed and direction, and site-specific safety thresholds.
If a site does not appear, it failed one or more of these checks and is unlikely to be flyable.
This does not guarantee unflyable conditions — simply that the algorithm does not flag it as a likely candidate for the forecast values for that specific time period. There are times when a site might be flyable for a short window (e.g., between 09h00 and 10h30) but because RASP values are available for specific time points (e.g., 08h00, 11h00, 14h00), this window won't show on the table and the site won't appear at all for the day.
This table is not the alpha and omega of paragliding weather forecasting — it's just another useful tool, and a damn good one at that 😉
The Emoji Scoring System
To keep the table simple yet meaningful, emoji markers provide quick scoring:
- 🤔 Maybe Flyable — surface wind looks decent, but the soarable alt is forecast below takeoff alt
- 👍 Likely flyable with soarable height above takeoff
- 🦅 Above + Average thermals ≥ 3 m/s
- 🔥 Above + Soarable height among the top 25% for the site historically
- 💥 Above + Soarable height among the top 5% for the site historically
🦅 🔥 💥 days usually mean strong thermal activity — better suited to experienced pilots.
Wind Speeds: Forecast vs Reality 🌪️
Surface winds typically read ~10 kph stronger in real conditions than the model predicts. A forecast of 19 kph often feels more like ~30 kph at takeoff — strong launches, faster landings, and increased turbulence risk.
Interpreting wind colours on RASP BlipMaps requires caution: the colour scale shifts based on the strongest wind anywhere on the map.
Site Gradings 👨🏫
Gradings (Basic / Sport / GH) are displayed to encourage safe flying and good airmanship. Pilots flying outside their rating increase the risk for themselves and others. The grading process is open — for example, Du Toits was regraded from Sport to Basic after a fire improved the landing environment.
Why Some Sites Aren't Listed 🤔
A site may be excluded because of:
- The site isn't a registered site
- Potential vegetation damage
- Landowner requests
- Crime concerns (e.g., Wolfgat attacks)
- Or simply because I'm not aware of it
If you feel a site should be included, let me know.
Learn to Forecast Like a Pro 🥳
If you'd like to understand:
- hcrit vs BL tops
- How to use RASP and other tools such as SkySight, Windy, Windguru, etc.
- What lapse rates tell you
- Why inversions can be risky
- Skew-T interpretation
- Daily forecast workflow
- Safe decision-making in thermic or laminar environments
…then my Online Weather Forecasting Course for Paragliding Pilots is designed for you. It's practical, Cape Town-focused, and will significantly deepen your confidence and accuracy.
Final Thoughts
The shift to Soarable Thermal Tops makes the forecast more intuitive and useful while preserving the deeper meteorological insight of Boundary Layer Tops — now displayed regionally, where they do a good job.
Use the forecast to spot opportunities. Then apply your own weather knowledge, checks, and judgement to decide whether to fly.
If you want to truly master weather forecasting, the online course will give your journey a running start 🚀
Fly smart. Fly safe. Fly often.
— Ria, Air School Paragliding
Learn weather forecasting in depth
The online weather forecasting course covers RASP, soundings, thermals, Cape Town sites, and a complete pre-flight system. R499 · Lifetime access on Payhip.
Buy Weather Course — R499