Weather forecasting

Forecasting the weather is essential for paragliding and we have listed a number of free sources which you may find useful.

First understanding the difference between the forecast (what is predicted to happen) and the actuals (what the weather is doing right now). – available as an app too. Great for forecasting everything (except thermal strength and soundings (use RASP)). Has different weather models – ECMWF, GFS, ICON-EU7, NEMS4.

Met Office – surface pressure charts are a good place to start with a general overview of the weather systems.

RASP models – These provide GFS forecasts with thermal models and soundings. Use either:

RASP site or XC Para or for the lazy use lazy RASP

XC Weather – still commonly used although the forecast resolution is not high (runs off GFS). Although the forecasts are poor it is still incredibly useful for live data. Note that the live data can typically be 1 hour or more old so local weather stations with trend data is usually better.

Brecon Beacons Mountain forecasts – an alternative to RASP which needs a subscription. Especially if you are travelling globally. Works well on phones and computers.

Forecast models explained

Which model to use?

Some important global weather forecasting models are GFS (US run), WRF (also US run), ECMWF (the “European model”), the Met Office’s Unified model (run from out of Exeter), NEMS4 (from Swiss meteoblue) and ICON (from DWD the German version of the Met Office). ECMWF has generally been shown to be more accurate than other models at forecasting over 5 to 10 days, although at 2 days out there is little difference in which model will be most accurate and it may be more useful to look and the most recently run model.

ECM and GFS will react to changing weather systems quickly as their models update every 6-7 hours.

The higher the resolution the forecast (i.e. 9 km is higher than 27 km), the more accurate the forecast will take account of topographical (e.g. mountain) and local (e.g. sea breeze) effects. This is especially true of mountainous areas like the Alps where the NEMS4 forecast may be most useful. NEMS4 has a resolution of 4km, compared with ECMWF at 9 km on and GFS at 22 km. The GFS forecasts used in RASP (including thermal forecasts) are run at 2, 4 or 12 km depending how far out the forecast is.

Top Tips!

It’s a good idea to first look at the overall weather system – using the synoptic charts. Then try looking at the different forecast models. If they are all in agreement, it is less likely there will be change in the forecast and the forecasts are more likely to be accurate. If there is a big difference between the forecasts then this is probably because there is an important weather event which will impact significantly on the forecast (such as formation of a new low, or passage of a frontal system) – you should be able to identify this on the synoptics.

Make sure you don’t confuse the forecast with the live data (“actuals”). You can find out what the weather is actually doing right now by looking at weather stations and webcams – check out out weather stations web page, or by using the SEW site reports group on Telegram. Also correlating the satellite images with the forecast can be useful for XC flying to determine where the good air masses and cloud cover are.

Remember the models only produce a prediction and do not take into account local conditions (especially when the resolution of the forecast is not as good). The forecast might give an accurate prediction of how the wind is flowing up high, but can’t necessarily predict how the wind is flowing around the hills and valleys down low. You need to imagine how the hills and valleys are funnelling and influencing the air flow and factor in the influence of hills and mountains. After a while you will get better at correlating the forecast with what actually happens on the hill.

Soundings and Thermal models

RASP and Skysight both provide thermal forecasts. The thermal parameters are mostly based on the amount of solar heating and the height of cloud base – and don’t take into account cloud suck or water on the ground.

The soundings and Skew-T diagrams are also available on RASP, Skysight and and can be very useful for understanding the forecast. There are other resources on the internet which can explain how to interpret these forecasts. Ask to join our Pilot Study Group on Telegram if you are interesting in knowing more.

We hope this has been useful for those of you starting out. Please let us know if you think there’s some useful key information we should include on this page.