How to Read a Paragliding Weather Forecast — Apps, Models and What Actually Matters

Most pilots look at a single number — wind speed — and decide from there. That is not weather reading; it is pattern matching. Real forecast interpretation involves understanding what the atmosphere will do across several hours, not just what wind speed the app is showing at a single altitude at 10:00. The pilots who consistently fly the good days and stay grounded on the dangerous ones are reading three or four parameters in combination, not one in isolation.

The Forecast Stack — What Behrooz Checks Before Every Sesimbra Day

Before every flying day in Sesimbra, the forecast check runs through the same sequence. The order matters — each parameter either gates or contextualises the next.

1. Surface wind direction and synoptic pattern

Everything starts here. For Sesimbra's coastal ridge, the flyable window requires wind within roughly 30° of NNW to NW. A north-northeasterly looks similar in speed but completely changes the site's character — the ridge becomes cross-wind or even tail-wind, and the usual launch and landing assumptions no longer hold. The synoptic chart (available on Meteociel or Windy's pressure overlay) shows whether the Azores High is positioned to drive a clean nortada or whether a low-pressure system will push wind from an unusual direction.

2. Wind speed at ridge height

For Sesimbra, ridge height is approximately 200–250 m AMSL. The forecast wind at that altitude — not surface wind — is the relevant number. Models typically report wind at 850 hPa (around 1,500 m) and surface level. Neither is exactly ridge height. Windy's altitude slider set to 500 m gives a reasonable approximation. At Sesimbra, the sweet spot for comfortable soaring is 15–25 km/h at ridge height. Below 12 km/h, the lift band becomes narrow and inconsistent. Above 30 km/h, launches become technical and the rotor zone behind the ridge requires careful circuit management.

3. Thermal potential and boundary layer depth

For XC or inland flying, boundary layer depth determines how high the thermals will climb. XCskies (now integrated into Skysight) gives a single-number rating and a visual map showing where thermals will reach and how strong they'll be. Skysight's "fly" rating, colour-coded by quality, is reliable enough to plan an XC day around. Look at the time-series view — the 11:00–15:00 window is what matters. A good autumn XC day in the Alentejo shows boundary layer depth above 1,800 m with trigger temperature reached by 10:30.

4. Cloud base and overdevelopment risk

A high trigger temperature with abundant moisture produces cumulus that grow quickly. The risk is overdevelopment — cumulus that shade out thermal triggers before you want to land, then build into cumulonimbus by afternoon. The XCskies Cu potential overlay and the skew-T diagram (available on University of Wyoming's atmospheric soundings) show whether the atmosphere is capped (thermals will be capped at a defined height) or uncapped (thermals may trigger deep convection by afternoon). In Portugal's dry summer and autumn, overdevelopment risk is lower than in alpine environments, but it is not zero.

The Apps and What They're Good For

Windy

The most versatile visualisation tool. Use it for understanding the synoptic pattern (pressure overlay), wind field at different altitudes (the height slider), and rain/cloud timing. It runs multiple models — GFS, ECMWF, AROME — and lets you compare them. When GFS and ECMWF agree, confidence is higher. When they disagree significantly, be conservative. The ECMWF model is generally more accurate for Portugal's Atlantic-influenced weather.

Skysight / XCskies

Built specifically for thermal flying. The daily "fly" rating, boundary layer depth maps, and thermal strength overlays are purpose-built for paragliding decisions. Reliable for planning XC days two or three days out. The time slider lets you see how conditions evolve across the flyable window. For coastal soaring, it is less useful — coastal ridge lift is driven by synoptic wind, not thermals, so the thermal maps are not the primary tool.

Meteociel

The preferred source for European synoptic charts. The ARPEGE and AROME models provide high-resolution forecasts for Portugal. AROME, at 1.3 km resolution, resolves coastal features well enough to show the sea-breeze interaction with the nortada — an important factor for late-afternoon Sesimbra flying when both flows are present.

Ventusky

A cleaner interface than Windy for quick checks. The temperature and CAPE overlays are useful for convective assessment. Some pilots find it more readable for presenting forecasts to non-pilot passengers who need to understand why today is not a tandem day.

What the Forecast Cannot Tell You

Models work at grid resolutions of 1–13 km. The actual wind at your specific launch, at the moment of launch, will differ from the model output — sometimes significantly. Thermal streets, sea-breeze fronts, and the acceleration of wind around headlands all occur at sub-grid scales. Local observation always overrides model output: if the grass at the launch is indicating 35 km/h and the model said 20, believe the grass.

This is one reason that guided flying in Portugal — where someone with 15+ years of local experience reads the day alongside the forecast — produces better outcomes than self-guided flying by a pilot who only knows the apps. The forecast is a planning tool. The local conditions are the go/no-go decision.

Understanding Portugal's dominant wind pattern — the nortada — is the foundation for reading coastal forecasts correctly. And for XC planning, the XC guide and the thermic conditions guide cover how to interpret the thermal forecast in the context of actual flying decisions in the Alentejo.